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PHYSIOLOGY  OF  THE 
NERVOUS    SYSTEM 


PHYSIOLOGY    OF     THE 
NERVOUS    SYSTEM 

BY     J.     P.     MORAT 

of  the   University  of  Lyons 
AUTHORISED     ENGLISH    EDITION 

TRANSLATED    AND    EDITED    BY 

H.  W.  SYERS,  M.A.,  M.D.  (Cantab.) 

Physician   to  the   Great  Northern    Central  Hospital 


WITH    263    ILLUSTRATIONS 

(66   in   CO  lour  i) 


W.    T.    KEENER    &    CO 

CHICAGO 

1906 


Vi_;)^VO 


butler  &  tanner. 

The  Selwood  printing  works, 

frome,  and  London. 


Ix- 


Translator's   Preface 

The  present  work  forms  the  portion  of  the  Treatise  on  Physiology 
by  Profs.  Morat  and  Doyon  which  is  devoted  to  the  Functions  of 
Innervation. 

In  completing  the  Enghsh  version  of  Professor  Morat's  well  known 
work  on  the  physiology  of  the  nervous  system,  the  translator  expresses 
the  hope  that  he  has  succeeded  in  interpreting  the  views  of  the  author 
with  fidehty  and  accuracy.  It  has  been  his  aim  to  adhere  as 
closely  as  possible  to  the  text  throughout  the  work,  making  use 
of  paraphrase  only  when  this  was  essential  to  clearness  of  expression. 

The  subject  treated  in  the  following  pages  is  a  most  complicated 
one  ;  but  there  can  be  no  doubt  that  this  volume  embodies  the  latest 
advances  in  our  knowledge  of  the  nervous  system  and  portrays  the 
most  recent  views  and  ideas  on  this  very  intricate  branch  of 
physiology. 

H.  W.  SYERS. 

WiMPOLB  Street, 
October,  1905. 


Preface 

In  every  living  being  a  double  current  of  matter  and  energy  is  present, 
running  in  a  definite  direction  which  never  varies.  In  these  two 
currents  the  transformations  of  energy  accompany  those  of  matter  ; 
they  are  sometimes  united,  sometimes  separated,  and  their  union  is 
the  starting  point  of  a  cycle  of  which  their  separation  emphasizes  the 
termination.  This  cycle  is  the  simplified  image  of  vital  evolution  ; 
and  in  it  the  first  traces  of  organization  are  sketched  out.  But  in 
proportion  as  this  cycle  becomes  complicated  and  elaborated  we  may 
observe  the  advent  of  fresh  cycles  more  or  less  resembling  it,  which 
superpose  themselves,  interfere  with  and  bestow  upon  it  a  new  value. 
Innervation  corresponds  to  a  cycle  of  this  nature. 

In  fact,  while  the  material  and  energetic  currents  proceed  from  the 
ingesta  to  the  excreta  through  the  intestines  and  the  vessels,  a  third 
and  an  incomparably  weaker  current,  that  of  the  nerves,  finds  for  itself 
distinct  and  separate  channels  and  intervenes  for  the  regulation  of 
the  two  former,  ensuring  for  them  their  most  effectual  employment. 
The  nervous  system  does  not  provide  force,  it  utilizes  it  ;  and  this 
duty  devolves  on  it  by  reason  of  the  perfection  of  its  own  organization. 
It  is  the  nervous  system  which  decides  at  what  moment  the  energy 
accumulated  by  the  living  being  shall  be  liberated,  in  other  words 
shall  leave  matter  and  exert  its  motor  functions.  This  point  it  decides 
with  the  assistance  of  information  communicated  by  the  organs  of 
the  senses,  and  by  means  of  a  sometimes  extremely  lengthy  work  of 
internal  elaboration  brought  to  bear  on  this  information  arriving 
from  the  exterior. 

In  short,  by  the  disturbances  entering  into  it  the  nervous  system 
receives  impressions  from  the  external  world  of  which  it  thus  obtains 
knowledge  ;  by  its  own  activity  it  forms  a  judgment  of  all  surrounding 
it  from  the  point  of  view  of  utility  ;  finally,  it  reveals  this  judgment 
by  a  motor  act  calculated  to  ensure  the  preservation  of  the  organism. 
Such  is  the  cycle  of  the  nervous  current  ;  it  implies  successively  an 
external  phenomenon  of  impression,  an  internal  phenomenon  of 
sensation,   another  external  phenomenon  of  motor  response  to  the 


viii  PREFACE 

impression,  itself  followed  by  another  internal  phenomenon  of  sensation 
registering  the  accomplished  movement.  In  the  nervous  system  all 
movement  induces  sensation,  all  sensation  induces  movement.  This 
system  amongst  its  most  extraordinary  attributes  possesses  a  power 
of  adjournment  concerning  the  events  depending  on  it.  These  events, 
which  on  a  reduced  scale  and  in  a  condition  of  representation  or  images, 
it  constructs  internally  with  the  data  furnished  by  the  senses,  it  pre- 
serves until  an  appropriate  moment  arrives  for  partially  realizing 
them  in  the  form  of  external  movements. 

From  the  fact  of  the  introduction  of  sensation  into  the  cycle  un- 
rolled in  the  nervous  system,  events  assume  for  it  a  particular  signi 
ficance  which  otherwise  they  would  not  possess.  According  to  the 
affective  tonality  (agreeable  or  painful)  of  the  sensation,  they  are 
either  favourable  or  the  reverse.  Obviously,  and  in  spite  of  the  errors 
which  it  may  commit,  the  living  being  seeks  the  former  and  avoids 
the  latter.  Whether  its  activity  is  free  to  choose  or  whether  it  is 
enclosed  in  an  inflexible  determinism,  is  a  problem  which  it  is  not  the 
province  of  physiology  to  inquire  into.  But  whether  rigid  or  elastic 
this  determinism  includes  a  new  element  and  factor,  sensibility,  which 
outside  of  the  living  being  is  either  wanting,  or  at  all  events  is  not 
apparent. 

The  relations  between  cause  and  effect  which  elsewhere  seem  so 
simple  are  here  on  this  account  extremely  complicated  and  modified. 
The  power  possessed  by  the  living  being,  and  more  especially  by  the 
nervous  system,  of  the  internal  preservation  of  external  events  by  their 
reduction  to  the  condition  of  representations  and  of  their  later  realiza- 
tion and  enlargement  in  the  form  of  visible  movements,  conveys  to 
us  the  false  impression  that  the  end  and  aim  of  an  act  is  the  cause 
of  this  act.  The  cause  of  an  act  cannot  be  in  the  future,  but  may 
be  in  the  memory  of  a  previous  act  of  the  same  nature  remembered 
as  being  either  useful  or  hurtful  and  which  on  this  account  determines 
the  direction  given  to  the  movement.  There  must  always  be  an  aim, 
a  general  or  particular  tendency  determined  by  the  sensory  nature 
of  the  living  being,  but  this  aim  is  an  effect  and  not  a  cause.  The  past 
always  involves  the  future,  but  in  this  past  the  living  being  knows  how 
to  choose,  and  when  it  recreates  it  it  does  so  as  much  as  may  be  to  its 
own  advantage  ;  whence  its  almost  indefinite  degree  of  perfectibihty. 

Thus  we  can  see  that  the  study  of  physiology  gives  rise  to,  or  at  any 
rate  borders  on,  problems  which  are  not  in  any  way  its  special  province  ; 
and  for  the  rest  demands  from  psychology  solutions  which  the  latter 
seeks  for  with  the  aid  of  its  own  methods.     A  kind  of  neutral  area, 


PREFACE  ix 

common  to  both  sciences,  exists  which  the  former  endeavours  to 
appropriate  by  pushing  farther  back  the  boundaries  separating  it  from 
the  latter.  Progress  must  inevitably  be  slow,  as  apart  from  the  fact 
of  this  study  bristhng  with  difficulties  of  every  kind,  methods,  in  spite 
of  the  efforts  of  a  host  of  inquirers,  still  remain  crude  and  unsuited 
to  the  infinite  dehcacy  of  the  organs  of  the  nervous  system  and  their 
component  elements. 

J.  P.  MORAT. 


Table    of    Contents 


INNERVATION 


Sensibimty  and  energy   . 
Sensibelity  and  determinism 
Sensibility  and  organization 
Excitability  and  sensibility. 


Action  and  Reaction.     Division 


Page 
1 
1 
2 

3 


FIRST  PART 
ELEMENTARY  NERVOUS  FUNCTIONS 

I.  Static  unity       .  ........ 

II.  Dynamic  unity  ........ 

Organisation  of  energy  ....... 

Multiple  forms  and  ti'ansformations  in  the  nerve 
Energetic    cycles.       Functions,    their    double    nature ;  their 
ciprocal  influence         ... 


Chapter  I 

THE  NERVOUS  ELEMENT 

A.  Static  condition  of  the  neuron  ;  anatomical  data    . 

I.  External  characters  of  the  neuron  ;   dimensions  . 

Form.     General  type      ...... 

Signification  of  the  parts.     Synonymy     . 
Axon.     Myelinated  and  non-mj^elinated  fibres 
Segmentary  cells  :    their  origin.     Collaterals     . 
Body  of  the  cell    ....... 

Cellulipetal  and  cellulifugal  prolongations 

II.  Dynamic  polarisation  ...... 

Experimental  basis.     Generali  ration.     Uncertainty    . 
Relative  importance  of  the  prolongations.     Adaptation 
nexiron.     Avoidance     ...... 

Objections      ........ 

III.  Individuality  of  the  neuron  ;    its  proofs 

IV.  Physiological  data.     Specificity  of  the  neurons     . 

Varied  forms.     Amacrine  cells.     Nervous  amoeboism 
Changes  of  form  in  the  dendrites  .... 
Functional  dissociations  ;    mechanism  and  localization 
Connexions  of  the  neiu'ons.     Adhesive  svipports 
Mitral  cells  of  the  olfactorj^  lobe,     Pericellular  baskets 
Spiral  fibre  ;    its  signification  .... 


of  the 


8 

9 

10 

12 

13 

15 

15 

17 

18 

19 
21 
23 
25 
26 
26 
27 
29 


xu 


TABLE    OF   CONTENTS 


Sutui'e    between    centrifugal 


B.  Dynamic  condition  ;    functions  of  the  neltron 

1.  Functions  of  internal  or  tropliic  connexion   . 
I.   Wallerian  or  descending  degeneration 

Laws   of   Waller.     Nutrition  and   conduction.     Trophic   centres 
and  functional  centres  ..... 

Generalization.     Cellular     laws.     Loss     of     excitability.     Struc 
tural  alterations 

TI.  Ascending    degeneration.     Coiidition    of    survival.     Clironiatolysis 

Its  phases.     Application  ..... 

Alteration  of  fibres.     Equivocal  meaning  of  words.     Ascending 

ncLU-ites      .... 

III.  Atrophic  degeneration 

IV.  Regeneration.     Nervous  suture  . 

Non-regeneration    of    nerve    cells. 

nerves  of  different  fiuictions         .... 

2.  Functions  of  external  or  nervous  union  properly  so  called 

Internal  and  external  acts  ;    properties  and  fmictions 

I.  Numerical  relation  between  the  exciting  energy  and  the  energy  svip 

plied  by  the  n^uscle    . 
IL  Excitability  and  conductivity 

Initial  shock  ;  specific  excitants  and  general  excitants 
Evidence  and  estimation  of  the  activity  of  the  nerve 

III.  Isolated  conduction  ...... 

Nervovis  induction  ..... 

IV.  Propagation  in  the  two  directions 
V.  Integrity  of  the  structiu-e  :    welding  of  the  nerves 

VI.  Local  excitability  of  the  different  parts  of  the  neuron.       Excita 

bility  and  conductivity 
VII.  Rate  of  conduction.     Method.     Period  of  propagation  and  latent 
period         .... 


Electrical  stimulus 


C.  Stimulation  of  the  nerves 

Gradation  of  the  effects.     Different  stimuli 

Preliiyiinary  conceptions    ....... 

A.  Electrical  energy  ;    its  units.     Electromotor  force  ;    volt 


Page 
29 

30 
30 

33 

33 

34 
35 

36 

37 
37 

38 

39 

39 

40 
42 
43 
43 

44 

45 

46 
47 

48 

49 

50 
50 
51 

52 

53 


olim  ; 
ampere  :    Quantity  of  electricity  ;    coulomb 

B.  Electric  fluxes,   discharges,    currents    (instantaneous,    continuous, 

constant)    .......... 

Polarization.  Non-polarizable  elements.  Acciunulators.  Cur- 
rent (oscillating,  alternating,  sinusoidal,  dii^hasic,  continuous, 
triphasic)   ..........        54 

C.  Induction  ;     lines   of  force  ;     field   of   force  ;     induction   (electric, 

magnetic)  ;   solenoids  ;  magnet     ......        54 

D.  Apparatus  for  stimulation.     Condensers.     Induction  ajoparatus    .        56 

Cells  ;  accumulators.     Rheotomes    .      .  .  .  •  .57 

E.  Apparatus  for  the  verification  and  the  measurement  of   electro- 

motor phenomena        ........        57 

Galvanometers.     Electrometer  of  Lippmann   ....        58 

Non-polarizable  electrodes       .......        58 


TABLE    OF   CONTENTS 


D.  Laws  of  electrical  stimulation 


I. 
II. 

III. 


IV. 
V. 


Problem  to  be  resolved.     Historical  ;    facts  and  opinions 
Old  formula      ...... 

Contradictory  facts  .... 

Conditions     to     be     realised.       Method.      Result 
Fixity  of  the  quantity  for  a  given  dtu'ation 
quantity     ...... 

Law  of  electrical  stimulation 

Methods  of  stimulation      .... 

Polar  influence       ..... 

Active  pole  ;  indifferent  pole.     Cathode,  anode 
the  current  ..... 

Unipolar  excitation  in  an  open  circuit    . 
Periodic  excitation.     Remark 


Ai'rangement 
variation  of  the 


Dii-ection     of 


Xlll 

Page 
58 

58 
60 
60 


61 
63 
63 

64 

65 
66 
67 


Chapter  II 

ENERGIES  OF  THE  NERVE 

A.  Energies  recognizable  in  the  nerve  ;  origin  and  succession 

Initial  state  ......... 

Final  state.     Transmitted  and  localized  energies.     Sources  of  energy 
and  stimulation  ....... 

Intensity.     Reserve  of  energy.     Heat  developed  by  the  nerve     . 

Electrical  energy  of  the  nerve         ..... 


B. 


I.  Current  of  repose       ........ 

Origin.  Derivation.  Pre-fexistence.  Alteration.  Axial  current 
II.  Negative  variation  ;   current  of  action.     Its  importance 

Wave  of  excitation  or  of  propagation.     Dii:)hasic  current 

Form  of  the  lines  of  flux.  Displacement  of  the  phenomena.  In- 
tensity of  the  variation        ....... 

Form  of  the  variation.     Unipolar  method.     Oscillatory  variation 

Nature  of  the  phenomenon.  Nervous  interferences.  Electrical 
resistance  of  the  nerve        ....... 

Part  played  by  the  cell  in  the  transmission  of  the  impulse  ;  dif- 
ferent argvmients         ........ 

Contradictory  experiments.  Modifications  of  the  cell  dm*ing 
fimctional  activity       ....... 

Chromatolysis  ........ 


C.  Consecutive  effects  of  the  stimulation  ;  fatig 
Definition.     Resistance  of  nerves  to  fatigue 
Temporary  dissociation  of  the  muscle  and  the  nerve. 
Conclusion.     Mechanism  of  fatigue 


Another  method 


D.  Electrotonus       ......... 

I.  Electrotonic  condition.     History.     Designations    . 

1.  Electrotonic  current.     Interference  with  the  ciu-rent  itself 

Rate  of  propagation  ...... 

2.  Paradoxical  contraction  ...... 

Difference    from    the    secondary    contraction.     Ineqiiality 
the  phases       ........ 


of 


73 
73 

73 

74 

75 

75 
76 

77 
79 

80 
82 

83 

84 

85 

85 

86 

86 

87 
88 

88 

89 

89 
90 
90 

90 


XIV 


TABLE    OF   CONTENTS 


Difference  between  electrotonus  and  negative  variation 

3.  Theories  of  electrotonus  .... 

II.  Electrotonus  ;  modifications  of  excitability  . 

Proof  of  excitability.     General  formula  of  electrotonus 
Positive  and  negative  modifications 

A.  Medium  current  ...... 

Ascending  and  descending  ciu^rent.     Excitability  and  condvic 
tibility    ....... 

B.  Strong  current      ...... 

Anelectrotonus  in  inhibition 

C.  Weak  cvurent        ...... 

Electrotonus  in  man  .... 

III.  Law  of  contraction   ...... 

Diagrammatic  scheme.     Discussion 

Law  of  Ritter-Valli         ..... 

Electrotonus  in  nerves  of  different  fvmctions  . 

E.  Different  employment  and  effects  of  electricity 

Action  of  the  magnetic  field  ;    electric  waves  and  rays 
High  frequency  currents        ..... 
Death  by  electricity      ...... 

F.  Nerve  poisons      ....... 

I.  General  poisons.     Anaesthetics    .... 
Chloroform  and  ether  ansesthesia 
Cocaine  ....... 

II.  Special  poisons.     Curare     ..... 
Strychnine.     Atropine.     Pilocarpine 


Page 
91 

91 

93 
94 
94 

95 

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96 

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100 

101 

103 

103 
104 
104 

106 
106 
107 
108 

109 
110 


SECOND  PART 
ELEMENTARY  SYSTEMATIC  FUNCTIONS 

Fundamental  data.     Relations  of  sensibility  to  movement    . 

First  Section 
NERVOUS  ORGANIZATION 
Its  scheme  .......... 

Chapter  I 

SENSIBILITY  and  MOVEMENT  ;    their  RELATIONS 

A.  The  roots  of  the  nervous  system  ;  their  functions     . 

1.  Simple  facts  ;    general  laws  ..... 

I.  Nerve  pairs.     Distinct  functions  .... 

Nature  of  these  functions        ..... 
Laws  of  Magendie  ...... 

II.  Current  of  entrance  and  of  exit  ;    order  of  succession 
Comparative  physiology  ..... 


117 


120 


124 

125 

125 
126 
128 

128 
129 


TABLE    OF   CONTENTS  xv 

Pagk 

III.  Functional  connexions.     Reciprocal  influences      .           .          *  .130 

2.  Organic  complications  ;   recurrent  sensibility  .           .           .          .  .132 

I.  Tlie  fact  and  its  conditions         .           .           .           .           .           .  .132 

II.  Raison  d'etre    .           .           .           .           .           .           .           .           .  .133 

III.  Generalization  of  the  fact            .           .           .           .           .           .  .134 

IV.  Recurrent  motricity             .           .           .           .           .           .           .  .135 

3.  Conventional  definitions  ;  sensorj''  field,  motor  field         .           .  .136 

I.  Comparison  of  the  anterior  and  posterior  portions  of  the  spinal  cord 

and  of  the  brain  ........      136 

II.  Mixture  of  sensory  and  motor  elements      .           .           .           .  .140 

III.   Pliysiological  proofs              .          .           .           .           .           .           .  .141 

B.  Spinal  nerves — Metamerism  .......      143 

I.  Radicular  metamerism  ;    spinal  metamerism         .           .           .  .144 

II.  Cutaneous  radicular  territories  ;    areas  of  anaesthesia   .           .  .145 

III.  Radicular  muscular  territories    .           .           .           .           .           .  .149 

IV.  Mixed  nerves 150 

C.  Cranial  nerves.     Functional  determinations      .          .          .  .154 

I.  Morphological  regularity  of  the  spinal  cord          .           .           .  .154 

II.  Irregularity  of  the  medulla  oblongata          .           .           .           .  .155 

Vertebral  theory  of  the  skull           .           .           .           .           .  .155 

A.  Physiological  characters  of  the  nerve  pair      .           .           .  .158 

B.  Relations  with  the  great  sjinpathetic    .           .           .           .  .162 

1.  Nerves  of  special  sense           .           .           .           .           .           .  .165 

a.  Olfactory  nerve     .          .          .  '        .           .          .          .           .          .  .166 

6.  Optic  nerve           .          .          .          .          .          .          .          .          .  .167 

c.  Auditory  nerve     .           .           .           .           .           .           .           .           .  .167 

d.  Gustatory  nerve    .           .          .           .           .          .          .           .           .  .168 

2.  Sensorj^  and  motor  nerves     .           .           .           .           .           .  .168 

a.  Oculo-motor  nerve          .          .           .           .           .           .           .           .  .168 

b.  External  oculo-motor  and  pathetic             .           .          .           .          .  .      16{> 

c.  Facial           .          .           .           .          .          .           .          .          .           .  .      16& 

A.  Peripheral  portion         .           .           .           .           .           .           .  .171 

I.  Deviation  of  the  features  of  the  face           .           .           .           .  .172 

II.  Elements  of  general  sensibility.     Recurrence;  anastomoses     .  .173 

B.  Deep  portion        .........      173 

I.  Motor  elements           .           .           .           .           .           .           .           .  .173 

II.  Sensorial  elements     .           .           .           .           .           .           .           .  .174 

III.  Ganglionic  elements.     Superficial  and  deep  petrosal  nerves      .  .174 

Filament  for  the  muscle  of  the  stapes.     Chorda  tympani     .  .174 

C.  Origins.      Intra-cranial  stin:iulation           .           .           .           .  .175 
Gustatory  sensibility.     Secretory  action,  vaso-dilatory       .  .      176 


XVI 


TABLE   OF   CONTENTS 


d.   Trifjemitvxl  ........ 

A.  Sensory  and  motor  functions  .... 

Sensory  paralysis.     Borrowed  sensorial  elements 
Motor  paralysis.     Intra-cranial  stimiilation 

B.  Connexions  with  the  great  sympathetic 

Secretory  elements    ...... 

C.  Trophic  distiu'bances     ...... 

Ophthalmic  ganglion  ;    its  nature 
Classification  of  the  elements.     Vaso-motors 
Elements  whose  function  is  undetermined    (trophic)  ;     posi 
tion  of  the  question       ..... 

D.  Indii'ect  action  on  the  senses         .... 

€.  Glosso-pharyngeal  ....... 

I.  Section.     Gustatory  paralysis      ..... 
Sensory  paralysis  ....... 

II.  Stimulation  within  the  skull.     Vaso-dilatory  elements  . 
Secretory  elements  ;   ganglia,  their  nature 

/.  Pneumogastric       ........ 

A  typical  arrangement.     Origin.     Ganglia.     Distribution 
Protoneurons  and  intracentral  neurons.     Specific  functions 

A.  ResiDiration 

Laryngeal  branch 
Recurrent  nerve 
Pulmonary  nerves 

B.  Circulation  .... 

Depressor  branch 
Cardio-inhibitory  elements 

C.  Digestion      .... 

Pharyngeal  branch.     Movements  of  the  oesopliagus 
Gastric  sensibihty.     Stimulation  of  the  origins  of  the  vagus 
Secretory  elements    ...... 

D.  Trophic  action.     Its  complex  mechanism 

■g.  Spinal  accessory  ....... 

Essentially  motor  function.     Forcible  extraction 

A.  Internal  branch.     Vocal  function.     Hoarseness,  aphonia 

Recurrent  nerves.     Asphyxia        .... 

B.  External  branch.     Its  function  in  effort 

h.  Hypoglossal  ........ 

I.  Effects  of  its  section,  motor  paralysis 
II .   Sensibility  by  anastomosis  ..... 

Ill .   Ganglionic  anastomosis  ;    vaso-constrictor  elements 


motor,  inhibitory 


Page 
177 


204 

204 
206 
206 


TABLE   OF  CONTENTS 


xvii 


Chapter  II 
PRIMARY  SYSTEMATIZATIONS 
Origin  of  the  nervous  system  ....... 

Its  development  ......... 

A.    COMMXnsriCATION    OF    THE    IMPULSES  ;     REFLEX    ACT 

Historical.     Extension  of  the  phenomenon         .... 

I.  Localized  reflex  acts  ....... 

Anatomical  data.     Connexions  between  elements.     Elements  of 
association  ........ 

II.  Symbolical  figure.     Ordinary  sense  of  the  word 

III.  Conscious,  sub-conscious,  and  unconscious  reflexes 

IV.  Elementary  reflex.     Centre  of  reflexion 
V.  Experimental  data.      Delay  of  the  stimulus.     Intensity 

VI.  General  direction  of  the  currents.     Method  for  its  determination 
Irreversibility  of  the  reflex  cycle     ..... 
Directive  organ      ........ 

its  laws         .... 


VII.  Dispersion  of  the  excitation  ; 
VIII.  Classification  of  the  reflexes 
IX.  Reflex  centres  of  the  spinal  cord 

X.  Sub-cortical  enceplialic  centres  . 
XI.  Reflex  cortical  centres        .... 
Reflexes  in  patholog3^     Medullary  reflexes 


Principal  centre,  Goll's  nucleus 


Cerebral  reflexes 


B.  Suspension  of  the  excitations  ;  action  of  arrest  or  of  inhibition 
I.  Its  scheme.     Apparently  paradoxical  datmn         .... 
II.  Analysis  of  the  system.     Distinct  existence  of  the  inhibitory  nerves 
Specificity  of  the  relations.      Inhibition    is    a    phenomenon   in- 
ternal to  the  nervous  system       ...... 

III.  Excitation  and  inhibition.     Reflex  and  inhibition  combined  in  the 

same  cycle  ....... 

IV.  Mechanism  of  inhibition     ...... 

V.  Secondary  effects  of  inhibitory  excitation  . 


C.  Conservation  of  the  stimulus. 

I.  Circulation  of  the  impulse 
II.  Avitomatic  stimulation 


Nervous  circulation 


D.  Classification  of  nerves     ...... 

I.  Initial  and  terminal  nevirons.     Sensory  and  motor  nerves 
II.  Intermediary  neurons  ...... 

Excitatory  and  inhibitory  neurons 

III.  Fimctional  systems  of  neurons  ..... 

IV.  The  centres        .  . 

1.  The  nervous  system  and  heat.     The  thermic  nerves 

i  I.  Cellular  exciting  function  for  the  disengagement  of  heat 
II.  Systematic  regulating  function  of  the  temperature 

2.  The  nervous  system  and  nutrition.     Trophic  nerves 
I.  Immediate  and  consecutive  influence.     Alteration  of   the   muscles 

P.  h 


Page 


211 

212 

214 
214 
215 

215 

217 
217 
218 
218 
221 
221 
222 

223 
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225 
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239 

242 

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247 
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248 

248 


xviii  TABLE    OF   CONTENTS 

Paqk 
II.  Alteration  of  the  skin  and  the  cornea  ;   unity  of  function  and  unity 

of  cellular  excitation  .......      249 

3.  The  nervous  system  and  animal  chemistry     .....      250 

Reactions  of  the  organism.     Chemical  equilibrium  .  .  .      250 

Rupture    of    the    ec£uilibrium.     Direct    nervous    action.     Indirect 


action 


251 


Chapter  III 
CONSCIOUSNESS  AND  UNCONSCIOUSNESS 


I.  Division  at  the  periphery  .... 

II.  Division  in  the  cerebral  cortex 
III.  Division  between  the  deep  and  peripheral    systems, 
of  the  boundaries        ..... 
The  problem  of  consciousness  ;    its  difficulties 


Variability 


A.  Dispersion  and  reflexion  of  the  excitations  ;    the  spinal  cord 

I.  Sensibility  in  the  spinal  cord        ..... 

A.  Stimulation  of  the  grey  matter  .... 

I.   Stimulation  of  the  centres  ..... 

II.  Determination  of  the  reflex  centres    .... 

B.  Stimulation  of  the  posterior  columns 

I.  Total  effect 

Endogenous  and  exogenous  fibres.     Isolated  stimulation  of  endo- 
genous fibres  ....... 

II.  Conclusion  ........ 

III.  Direct  and  indirect  prolongation  of  the  sensory  roots 
Cerebellar  tract  ....... 

Tract  of  Gowers        ....... 

Deep  lateral  tract  and  lateral  ground  Jiiuidle 

IV.  Stimulation  of  the  lateral  column       .... 

C.  Section  of  the  medullary  tracts  .... 
I.  Hemisection  of  the  spinal  cord  ;    preservation  of  sensibility 

Hypersesthesia  ........ 

Crossed  anaesthesia    ....... 

II.  Explanation  ;    decussation  of  the  sensory  tracts    . 

Syndrome  of  Brown-Sequard      ..... 

III.  Sensory  medullary  paths  of  tlie  deep  organs 

IV.  Important  part  played  by  the  grey  matter    in    sensory  transmis- 

sion      ......... 

2.  Motility  in  the  spinal  cord  ...... 

Motor  field.     Pyramidal  tract.     Fundamental  tract 
Cerebello-spinal  motor  paths.     Anterior  marginal  tract 

I.  Stimulation  of  the  descending  tracts 
II.  Decisive  experiment  ...... 

III.  Quantitative  difference       ...... 


256 

257 

257 

258 

259 

260 

260 

260 
262 

262 
262 

262 

263 
265 
267 

268 
268 

269 

270 

270 
271 
271 

272 
274 

274 

275 
276 

277 
277 

279 
279 
280 


TABLE   OF   CONTENTS 

IV.  Section  of  the  antero-lateral  columns 

V.   Part  played  by  the  grej^  matter  in  motor  transmission 
VI.  Direct  and  crossed  action  ...... 

Syncineses  ........ 

Mode  of  association  of  the  neurons    .... 


XIX 

Page 
281 

282 
283 

283 
284 


B.  Animal  life  and  organic  life  ;  the  great  sympathetic 

1 .  The  two  lives  ;   theu-  distinct  representations  in  the  nervovis  system 

So-called  cerebro-spinal  systems  and  great  sympathetic     . 
Signification  attributed  to  these  terms  .... 

Anatomical  differences  between  the  two  systems    . 
The  limits  of  the  great  sympathetic      ..... 
Its  sensory  elements.     Metameric  arrangement.         Cranial      sjanpa 
thetic        .......... 

2.  The  grey  matter  of  the  ganglia  ;    its  functions 

Ganglia  ;    motor  nuclei  ....... 

Apex  of  the  lieart  ;    mj'ogenic  and  neurogenic  doctrines 
Periodic  inexcitability  ;    refractory  phase  ;    compensating  repose 
The  nervous  network  of  the  heart's  apex       .... 

Anodic  stimulation  ;    its  inhibitory  effect.     Anti-tonic  action  of  the 

vagi . 

Conclusion.     Functional  part  played  by  the  different  ganglia  of  the 

heart         .......... 

Action  of  oxygen  on  the  movements  of  the  heart 

A.  Tonic  power  ........ 

B.  Reflex  power        ........ 

C.  Inliibitory  power  ;...... 

I.   Systems  of  the  life  of  relation  and  of  the  vegetative  life,  re 
semblances  and  differences    .  .  .  .  ■ 

II.  Mechanical  and  chemical  acts  ;    contraction,  secretion 

III.  Specific  excitations  of  the  sensory  nerves  of  the  deep  organs 

IV.  Experimental  data  ...... 

V.  Mixtm-e  of  stimulating  and  inhibitory  influences 

3.  Special  functions  of  the  gi-eat  sjanpathetic  . 

Historical,  initial  fact         ...... 

Vaso-motor  function  ...... 

Double  motor  and  inliibitory  function 
Secretory  function.     Inhibito-secretory  function 
Vaso-motor  lymphatic  fmiction.     Clu'omatic  fionction 

4.  Systematization  of  the  great  sympathetic  ;    its  two  ordei's  of  fibres 

of  projection  ..... 

Granglionic  metamerism  and  spinal  metamerism 
Association  of  the  metameres     . 
Summary  .... 

5.  Topographical  determinations 

A.  Superior  half 

I.  Elements  of  medullary  origin 
First  grouj)  :  sympathetic  iimervation  of  the  head  and  necl 


286 

287 

288 
288 
290 
291 

292 
297 

297 
298 
300 
303 

304 

305 
306 

309 
311 
311 

312 
313 
314 
314 
315 

316 

317 
317 
318 
319 
320 

322 

322 
324 
328 

331 

332 

332 
333 


XX  TABLE    OF   CONTENTS 

II.  Elements  of  bulbar  origin 
Second  gi'oup  :   sympathetic  nerves  of  the  superior  limb 
Vertebral  nerve         ..... 
Third  group  :    thoracic   visceral  nerves 

B.  Inferior  half        ..... 
First  or  caudal  group.     Sympathetic  nerves  of  the  trunk 
Second  grouj^,  or  that  of  the  inferior  limb 
Third  group,  or  that  of  the  abdominal  viscera 
Elements  of  medullary   origin 
Elements  of  bulbar  and  sacral  origin 
Abdominal  viscera  and  those  of  the  pelvis 


Pagi': 
335 
338 
339 
340 

341 
341 
341 
342 
342 
343 
343 


C.    TrANSMLSSION  and    centralization   of   the   stimuli  ;     THE      MEDULLA 
OBLONGATA  ...... 

Proper  functions    ...... 

1.  Sensibility  and  motricity  in  the  medulla  oblongata 

A.  Motor  paths  ;    anterior  pyramids 
Decussation.     Alternate  hemij^legia 

B.  Sensory  paths.     Fillet  {Ruban  de  Reil)  . 

2.  Local  reflexes      ...... 

I.  Reflex  cry  ...... 

II.  Blinking  of  the  eyelids       .... 

III.  Conjugate  deviation  of  the  eyes 

Convergence  for  adaptation  to  distances 

IV.  Sympathetic  origins  .... 
V.  Deglutition        ...... 

VI.  Mastication.     Suction  .... 

3.  General  reflexes  ..... 

I.  Common  sensorium    ..... 
II.  Locomotive  functions.     Part  played  by  the  pons 

A.  Respiration            ..... 
I.  Vital  knot 

II.  Influence  of  the  composition  of  the  blood 

B.  Circulation  ...... 

I.  General  bulbar  vaso-motor  centre 

•     II.  Vaso-motor  reflexes.     Cardio-inhibitory  centres 

C.  Movements  of  the  pupil 
I.  Dilator  reflex  of  the  iris 

II.  Irido-constrictor  or  photo-regulative  reflex 

D.  Secretions  ...... 

i  Diabetic  puncttu*e  .  . 


347 
347 

349 

349 

350 

352 

354 

355 
355 
355 
356 

357 
357 
359 

359 

359 
3G0 

361 
361 

362 

363 
364 
364 

365 
365 
366 

366 
367 


Chapter  IV 
SUPERIOR  SYSTEMATIZATIONS 
A.  Orientation  and  equilibrium  ;    the  cerebellum 
Historical  ....... 

Comparative  anatomy         ..... 


372 
373 
375 


TABLE    OF   CONTENTS  xxi 

Page 

1.  Conditions  of  equilibriiun     ........      376 

I.  Reciprocal  relations  between  motor  effect  and  sensory  excitation    .      377 

II.   Sense  of  equilibrium  .  .  .  .  .  .  .  .378 

III.  Automatic  action       .........      379 

IV.  Sources  of  stimulus  .........      379 

V.  Progress  of  the  impulses  ........      380 

The  cerebellum  and  reflex  movements     .  .  .  .  .381 

Anatomical  data    .........      382 

Connexions  of  the  cerebellum  studied  according  to  degenerations  .      384 

2.  Experimental  data  and  those  of  observation  ....      385 

A.  Cerebellar  peduncles  ........      385 

I.  Inferior  cerebellar  peduncles  .                      .           .385 

II.  Middle  cerebellar  peduncles  .......      386 

III.  Superior  cerebellar  peduncles  .......      387 

IV.  Olives  and  nuclei  of  the  pons  ;  their  connexions    ....      388 
V.  Movements  of  rotation       .  .           .           .           .           .           .           .389 

B.  Effects  of  destruction  of  the  cerebellmn   .....      391 

I.  Unilateral  destruction.     Consecutive  effects  .391 

11.  Total  destruction       .........      393 

III.  Destruction  of  the  vermis  .......      394 

IV.  Predominating  direct  action        .......      394 

C.  Electrical  stimulation  of  the  cerebellum    .....      394 

I.  Agreeinent  of  the  results  ........      395 

II.  Functional  relations  of  the  cerebellmii  and  the  brain  .  .      396 

III.  Cerebellar  vertigo      .........      396 

B.  The  emotions.     Optic  thalamus  and  corpora  striata 
I.  Reflex  and  conscious  voliintary  nervous  acts       ....      398 
II.  Emotional  acts  .........      398 

1.  Affective  tone.- — Pleasui-e  and  pain        ......      400 

I.  Their  link  with  the  different  orders  of  sensibilitj-  .  .  .401 

II.  Determinative  condition     .  .  .  .  .  .  .401 

III.  Non-specific  nature    .........      402 

IV.  Habitual  field  ..........      402 

V.  Stimulation  of  the  nerve  trmiks  ......      402 

VI.  Stimulation  of  the  central  inasses       ......      403 

VII.  Stimulation  of  the  cerebral  cortex      .....      403 

2.  Expression  of  the  emotions  .......      404 

I.  Language  of  the  emotions  .......  404 

II.  Innateness  of  the  emotional  mechanisms     .....  405 

III.  Emotional  expressions  on  the  hiuuan  face.     The  muscles  of  expres- 
sion ...........  406 

3.  Anatomical  data  .........  409 

The  cerebral  cortex  and  the  optic  thalamus        .  .  .410 

4.  Functions  of  the  optic  thalamus  .  .      "     .  .  .410 

A.  Clinical  facts  .  .  .  .  .  .  .  .  .  .411 

I.  SuiDerior  and  inferior  facial  .  .  .  .  .  .  .411 

II.  Peripheral  and  deep  facial  .  .  .  .  .  .411 


XX  u 


TABLE    OF    CONTENTS 


III.  Paralysis  of  the  voluntary  function    ..... 

IV.  Voluntary  jDaralysis,  preservation  of  the  emotional  expressions 
V.  Paralysis  of  the  emotional  expression,  preservation  of  the  voluntary 

movements  ...... 

B.  Experimental  facts  ..... 

I.  Motor  tracts  special  to  the  optic  thalamus 

II.  Functional  relations  between  the  cortex  and  the  optic  thalamus 
III.  Emotional  reactions  of  the  deep  organs 

5.  Functions  of  the  corpus  striatum 

I.  Experimental  data     ...... 

II.  Supposed  function     ...... 

Nucleus  of  Luys  ;    corpora  quadrigemina  ;    mammillar 

6.  Instinct  in  man  and  animals         .... 

Characters  of  instinct  ..... 

C.  Intelligence  ;    the  brain     ..... 

1.  Anatomical  data  ;    structure  and  connexions 

A.  Cortex.     Structure  ...... 

Human  brain    ....... 

Brain  of  the  primates  ;    monkey 

Brain  of  the  carnivora  ;    dog     .... 


y  bodies 


internal    capsule,    crura   cerebi-i,  cortical    fillet 


B.  Corona   radiata  ; 

(Ruban  de  Reil)        .... 
Crura  cerebri     ..... 

2.  The  psychical  functions  of  the  brain    . 

A.  Ablation  of  tlie  cortex  in  mammals 
I.  Scheme  of  experiment 

State  of  the  senses.     Nutrition.     Instincts.     Emotions 
II.  Earlier  experiments  ..... 

III.  Cerebral  cortex  and  sensation    . 

IV.  Sensations  which  have  undergone  reduction 

B.  Ablation  of  the  cortex  in  birds 

C.  Ablation  of  the  cortex  in  the  frog    . 

3.  Exchanges  between  the  brain  and  the  blood 

I.  Indirect  calorimetry 

II.  Heat  and  thought     . 

III.  Cerebral  circulation  . 

IV.  Vaso-motors  of  the  brain 

Stimulation  of  the  cervical  sympathetic 

Hypoj^hysis  . 

Epiphysis 

D.  Cerebral  localizations 

1.  Localizations  in  consciousness 
I.  Initial  fact 
II.  Discord  in  the  interpretation 
III.  Number  and  situation  of  the  excitable  areas 

Extension  of  the  excitable  area.     Motor  and  sensory  centres 


Page 
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413 

413 

414 
415 
415 
416 
417 

419 
420 
421 

421 
422 

424 

427 

427 

432 
434 
435 

440 
445 

445 

446 

446 
447 

447 
449 
450 

451 
451 
451 

453 
454 
454 
456 
456 
456 
457 

457 

458 

458 
459 
460 
461 


Relative  characters.     Artificial  excitation  and  normal  activity  .      462 


TABLE    OF   CONTENTS 

IV.  Localized  ablations    ..... 

V.  Disturbances  of  sensibility 
VI.  Comparison  of  motor  and  sensory  distm*bances 
VII.  Evolution  of  the  question 

VIII.  The  tactile  system 

IX.  The  sensorial  systems.     Localization.     Differentiation 

Opposition  of  the  points  of  view.     Difference  in  the  criteria 

2.  Localizations  in  unconsciousness  .... 

A.  Respiration      ....... 

Movements  of  the  larjmx  .... 

B.  Circulation.     Vaso-motor  area 
Basal  ganglia.     Heart.     Thermo-regulating  function 

C.  Digestive  functions.     Mastication.     Swallowing.     Movements 

the  stomach  ...... 

Cardiac  orifice.  Body  of  the  stomach.  Pylorus 
Movements  of  the  intestine  .... 
Sphincter  of  the  anus.     Rhythmic  contractions  . 

D.  Secretions        ....... 

Lachrymal  secretion  .  .  .  . 

E.  Retraction  of  the  bladder         .... 

F.  Genital  organs  ...... 

Trophic  influence  of  the  brain  ... 


of 


XXlll 

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466 
467 
468 
468 
469 
470 

471 
472 
472 

473 
473 

475 

476 
476 
477 

478 
479 

480 
480 

481 


Second  Section 
SPECIFIC  INNERVATIONS 


Specific  activities  ........ 

I.  Sensory  field,  its  divisions  ...... 

II.  Specificity  of  the  excitant  ...... 

III.   Specificity  of  the  sensation  ...... 

Uniformity  of  function.     Specificity  of  the  neiii'ons 
Definite  relation  between  the  imioression  and  the  sensation 
Seat  of  the  sensation     ....... 

Sensation   considered   with   regard   to   time.     Specificity   of   the 

sensorial  systems  ........      494 


488 

488 
488 
489 
489 
491 
493 


Chapter  I 
TACTILE  INNERVATION 

A.  Anatomical  data.     Sub-dermic  apparatus 

Intra-dermic  apparatus.     Distribution 
Intra-epidermic  ramifications 

B.  Data  of  physiological  observation 

I.  Natixre  of  the  excitants 
II.  Experimental  dissociation 
III.   Persistence  of  the  impression     . 


497 

498 
499 

500 

500 
501 
502 


XXIV 


TABLE   OF   CONTENTS 


ingomelic  dissociation 


of  the 


IV.  Primitive  element  of  tactile  sensation 
V.  Stereognostic  sense    , 

A.  Projection  on  the  grey  axis 

I.  Passage  through  the  spinal  ganglia 

II.  The  posterior  radicular  fibres     . 

III.  Dispersion  of  the  excitation 

IV.  Short  circuit  ;    reflex  action 
V.  Long  circuit  ;    conscious  action.      Syr 

sensations 
VI.  Localizing  hypothesis 
VII.  Bulbar  reflexes 

B.  Cortical  tactile  area 
I.  Cortical  localization  of  sensibility.     Sensitivo-motor  area 

II.  Imperfect  superposition  of  the  sensory  and  motor  areas 

III.  Another  localizing  formula.     Critical  examination 

IV.  Apparent  dissociation  of  sensibility  and  motricity  . 
V.  Multiiale  connexions  ...... 

VI.  Isolation  ......... 

Primary  and  secondary  sensations 

VII.  ■  Exteriorization  of  the  sensation.     Illusions  of  those  who  have  under 

gone  amputation  of  a  limb  .... 

VIII.   Localization       ........ 

C.  The  tactile  area  from  a  motor  point  of  view 

A.  Limitation  .  .  .  .  .  .  .  . 

Divisions.     Subdivisions  ..... 

B.  Stimulation  ....... 

Excitability  of  the  grey  and  white  matter  comj^ared 

I.  Delimitation  of  the  motor  areas  determined  by  stimulation 
Cerebral  metamerism      ...... 

II.  Characters  of  the  movements.     Primary     and     secondary     move- 
ments ......  .  . 

III.  Motor  centre  of  language  ..... 

Corpus  callosum.     Co-ordinated  sensori-motor  systems 

IV.  Crossed  and  direct  action  ..... 

Movements  of  the  eyes.     Movements  of  the  tongue 
Mastication.     Swallowing.     Laryngeal     movements 
Bulbar  and  pseudo-bulbar  paralyses.     Epileptiform  crises 

D.  Muscular  sense.     Cin^esthesic  impressions 

Synonymy 

A.  Muscular  sensibility 

I.  Its  proofs  ..... 

II.  Irritability  and  muscular  consciousness 

III.  Sensory  nerves  of  the  muscles  . 

IV.  Independence  of  the  muscular  contractility  and  sensibility 
V.  Different  modalities  of  muscular  sensibility  . 


Page 
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5oa 

503 

504 
505 
506 
507 

508 
509 
510 

511 

511 
514 
516 
518 
519 
520 
521 

521 

522 

523 
524 
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526 

526 

528 

528 
531 
533 

534 
535 
536 

537 

541 
542 

544 

544 
544 
545 

546 
546 


TABLE    OF    CONTENTS 


XXV 

Page 
54C 
547 


B.  Osseous  sensibility         .....•• 

C.  Articular  sensibility       .....•• 

I.   Conceptions  furnished  by  the  different  sensibilities.      Position  of  the 

limbs 547 

II.  Cortical  localization  of  the  muscular  sense,  and  the  cinasthesic  im- 
pressions   ..........      548 

III.  Feeling  of  effort.     Muscular  effort.      Psychical  effort      .  .  .549 

IV.  Voluntary  excitation  .  .  .  .  .  .  .  .551 

Sensation  and  movement  in  the  fcetus    .....      552 


Chapter  II 
VISUAL  INNERVATION 

A.  From  the  retina  to  the  cerebral,  cortex 

I.  Morphological  signification 

II.  The  retina  is  a  nervous  centre 

III.  Optic  radiations         .... 

IV.  Progressive  transformations  of  the  nervous  act 
V.  Dispersion  of  the  impulses  in  the  system 

B.  Impression  on  the  retina  ;    rods  and  cones 

I.  Functional  differences         ...... 

II.  Macular  tract  and  peri-macular  tract 

III.  Direct  and  crossed  tracts  ..... 

IV.  Corresponding  areas  ;    identical  points  of  the  retina    . 
V.  Homonymous  hemianopsia  ..... 

VI.   Persistence  of  the  retinal  impressions.     Consecutive  images 
VII.  Unity  of  sensation  in  binocular  vision 

C.  Cerebral  visual  sphere       ...... 

I.  Former  experiments  and  observations 

II.  Cuneus  and  calcarine  fissm-e.     Lesions  of  the  angular  gyrus 
III..  Surface   of   projection.     Geometrical   projection.     Compound   pro- 
jection       .....••• 
IV.  Luminous  sensation  and  mental  vision 

V.  Different  kinds  of  blindness.     Conditions  of  their  production 
VI.  Conceptions  of  form,  space,  locality,  orientation 
VII.   Physical  image,  psychical  image  .... 

VIII.  [Empty  space,  occupied  space.     Exteriorization  of  the  sensation 
IX.  Physical  and  psychical  blindness 
X.  Verbal  blindness        ...... 

D.  Motor  effects.     Paths  of  return 

I.  Localities  for  reflexion  of  the  impulses 

II.  Different    functional  associations 

III.  Retino-pupillary  reflex        ..... 

IV.  Associated  movements        ..... 
V.  Dextrogyral  and  levogyral  hemi-oculo-motor  nerves 

VI.  Elevator  and  depressor  nerves  of  the  axis  of  vision 
VII.  Movements  of  the  eye  in  their  relations  with  the  muscles  and  the 
motor  periijheral  nerves 
VIII.  Inhibitory  paths         .... 


554 

554 
556 
556 
558 

558 

560 

561 
562 
562 
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573 
574 

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579 
580 
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586 


XXVI 


TABLE   OF   CONTENTS 


IX.  Other  co-ordinated  movements  of  the  eyes 
X.  Movements  of  the  eyelids.     Protective  reflex 
XI.  Movements  of  the  head     .... 
XII.   Niimerous  motor  areas  for  the  eyes  . 
XIII.  Cerebellar  influence    ..... 

Signification  of  the  centrifugal  fibres  liaving  their  terminations  in 
the  sensory  elements  ....... 


Page 
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597 


Chapter  III 
AUDITORY  INNERVATION 
Comparative  anatomy  and  j^hysiology 


Baresthesic,     mantesthesic,   seisa?sthesic 


A.  Labyrinthine  stimulation 

Different     appropriations. 

functions  ....... 

1.  The  sense  of  space    ...... 

1.  Stinauli  of  extra-somatic  origin    .... 
II.   Stimuli  of  intra-somatic  origin     .... 

III.  Link  between  the  muscular  tonus  and  the  motor  power 

IV.  Analysis  of  the  perceptions  of  space 
V.  Superposition  and  synthesis  of  the  notions  of  space  furnished  by 

each  sense  ...... 

Objective  and  subjective  orientation.     Vertigo 

2.  Specific  sensation  or  that  of  auditory  tonality     . 

I.  Auditory  field  ....... 

II.  Fusion  of  the  impulses  in  the  sonorous  sensation 

III.  Damping  of  the  vibrations  special  to  the  ear 

IV.  Rate  of  the  development  of  the  sensation 

B.  Transmission  from  the  ear  to  the  cerebral  cortex 

Vestibular  nerve    .... 
Cochlear  nerve       .... 

C.  Auditory  cortical,  area 

Physical  deafness  ;    psychical  deafness 
Verbal  deafness,  or  that  for  words 
The  ideas  of  space  ;    their  relation  to  the  cortex  and  the  different 
senses 

D.  Paths  of  return 

Muscles  of  the  external  ear 
Muscles  of  the  middle  ear 


(iOl 
G03 

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607 

608 
608 
609 
610 

611 
611 

613 

613 
614 
614 
615 

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617 

622 

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624 

625 

626 

627 
627 


Chapter  IV 
OLFACTORY  AND  GUSTATORY  INNERVATIONS 
A.  Olfactory  system         ........ 

Field  for  reception  of  the  im^jressions         .  .  .  . 


628 
629 


TABLE    OF   CONTENTS 

1.   Bulbar  portion  of  the  system     .... 

Its     organization.      Connexions     between     elements. 

relations 
Functional  varieties. 


Other  connexions 

2.  Cerebral  portion  ..... 

Limbic  convolution  of  the  osmatics 
Osmatics  ;  anosmatics    .... 

3.  Evolution  of  the  olfactory  system  and  of  its  function 

a.  Inferior  vertebrata.     h.  Superior  vertebrata 

4.  Constitution  of  the  olfactory  system 

Absence  of  experimental  and  clinical  data 

5.  Motor  olfactory  jiaths         ..... 

Reflexes  of  adaptation.     Relation  with  general  sensibility 

B.  Gustatory  system        ....... 

1.  Field  of  impressions.     Papillfe  of  the  tongue.     Taste  buds 

2.  Nerves  of  taste  ....... 

Unknown  cortical  localization.     Reflexes  of  adaptation 


Numerical 


XXVll 

Page 
.      629 

6.30 
631 

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634 

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642 

643 

643 

644 

644 
646 
647 


•  Chapter  V 
LANGUAGE  AND  IDEATION 

Emotional  expressions 

A.  Formation  of  words  and  of  ideas 


L  Representations  in  consciousness 
I.  Method  of  analysis.     Physical  and  n 
II.  Multiple  operations  of  the  niind 
Primordial  element,  sensation 


oral  world 


III.  Analysis  and  synthesis,  formation  of  the  images  of  objects 

2.  Motor  acts  of  spoken  and  written  language 

Deaf -mutism.     Part  played  by  the  muscular  sense 
Automatic  language 

3.  Internal  language       .... 

Internal  resonance.     Motor  tendency 

I.  Intelligence  and  consciousness    . 
II.  Attention  ..... 

III.  Fatigue     ...... 

1.  Language  and  cerebral  localizations 

Pathological  dissociation  of  the  elements  of  language 

1.  Aphasias  known  as  cortical         ..... 

A.  Motor  aphasia,  agraiahia  ..... 

B.  Sensorial  aphasia.     Verbal  deafness,  verbal  blindness 

Sensorial  types.     Amusia,     Amimia 


648 
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650 

652 

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654 
656 

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657 

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663 

663 
664 

665 


XXVUl 


TABLE    OF   CONTENTS 


2.  Aphasia  by  default  of  conduction 

Schematic  constructions 

Seat  of  ideation     .... 

Automatism  and  intelligence 

3.  The  area  of  language  ;    its  constitution 

Fibres  of  association 
Fibres  of  projection 

C.  Processes  and  Organs  of  association 

Anatomical  hyjoothesis.     Contestations.     Experiments 
Moderating  functions  of  the  frontal  lobe.     Inhibition 


D.  Sleep 


Dreams  .... 

Supposed  Mechanisms.     Necessity 
Artificial  sleep.     Hypnosis. 
Personality  :    its  disaggregations 
Spiritualism 


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674 


Innervation 

In  the  living  being  all  the  phenomena  appertaining  to  crude  matter 
are  observable,  but  the  converse  does  not  hold  good.  It  is  obvious 
that  a  being  endowed  with  life  possesses  characteristics  and  presents 
manifestations  for  which  in  dead  matter  we  can  find  no  parallel  ;  and 
the  most  marked  feature  distinguishing  the  one  from  the  other  is  that 
of  sensibility.  Here  is  brought  before  our  notice  a  fact  of  a  purely 
internal  nature,  eluding  observation  as  it  is  generally  understood  in 
science,  but  which  common  sense  constrains  us  to  attribute  to  beings 
resembling  ourselves,  while  at  the  same  time  denying  it  to  all  objects 
in  which  this  resemblance  cannot  be  discerned. 

Sensibility  and  Energy. — This  attribute,  sensibility,  cannot  in  the 
living  being  act  as  a  substitute  for  the  energetic  phenomena  of  matter  ; 
it  is  merely  superposed  to  these  phenomena,  and  connected  with  them 
by  a  double  reciprocal  link.  They  preside  over  it  in  the  sense  that  a 
subject  gifted  with  feeling  must,  of  necessity,  require  an  object  to  be 
felt  ;  and,  on  the  other  hand,  sensibility  exercises  a  control  over  these 
phenomena  of  energy,  inasmuch  as,  though  incapable  of  modifying  them 
as  a  whole,  it  ca.n  still  regulate  and  control  them  in  their  execution  of 
functions  directed  towards  an  end  of  which  the  living  being  itself  is 
conscious. — This  reciprocal  link  not  only  controls  the  relations  of  the 
living  being  with  all  surrounding  objects  ;  it  is  also,  and  simultaneously, 
the  distinctive  feature  of  its  organization.  In  its  development,  as 
much  ontogenetical  as  phylogenetical,  it  is  the  living  being  which  is  at 
once  both  artificer  and  final  cause. — From  this  double  link,  so  frail 
in  itself,  and  yet  so  intimate,  proceeds  the  iinity  of  beings  endowed  with 
life,  and  in  this  organism,  where  each  part  depends  on  the  whole,  and  the 
whole  on  each  part,  a  synthesis  is  effected  which  confers  upon  it  its 
individnality.     This  prodigy  of  complexity  is  also  a  prodigy  of  unity. 

Sensibility  and  Determinism. — A  science  having  for  aim  the  study  of 
a  being  so  constituted  should  never  lose  sight  of  this  double  character, 
and  more  especially  when  appealing  to  the  methods  and  general  prin- 
ciples of  other  sciences.  Dissociated  and  brought  back  to  the  crude  state 
of  common  matter,  the  primary  elements  constituting  the  li\ang  being 
reveal  to  us  in  their  reactions  the  same  inflexible  constancy  that  charac- 

p.  ^  B 


2  INNERVATION 

terises  the  laws  known  as  physico-chemical  ;  yet,  associated  in  the 
individual,  their  grouping  and  organization  display  that  infinite  variety 
and  contingency  whence  individuality  is  derived.  How  can  this  pro- 
ceed from  that  ?  How  can  that  which  is  invisible  in  the  element 
become  apparent  in  the  whole  ?  To  these  questions  we  can  find  no 
answer  ;  but,  in  science  as  elsewhere,  it  is  always  imprudent  to  run  foul 
of  the  information  given  by  common  sense,  and  a  problem  is  not  solved 
when  one  of  its  terms  has  been  omitted. 

The  mind,  desirous  of  being  logical,  is  in  fact  at  first  offended  by  this 
contrast,  and  endeavours  to  annihilate  it  by  evading  one  of  the  two 
points  of  view.  The  rigid  determinism  of  purely  energetic  sciences  has 
been  transported,  without  restriction  or  selection,  into  biological  science. 
In  the  past,  and  even  at  the  present  time,  physiology  has  overlooked,  and 
still  overlooks,  the  fact  of  the  being  which  it  studies  possessing  sensi- 
bility ;  and  has  in  every  case  refused  to  acknowledge  this  sensibility  as 
a  causal  or  conditioning  influence  in  the  determinism  of  vital  phenomena. 
It  has  carefully  arranged  the  balance-sheet  of  the  forces  of  the  organism, 
while  taking  no  interest  in  the  function  which  regulates  their  em- 
ployment. As  physical  science  finds  no  place  for  sensibility,  neither  has 
physiology  accorded  it  one.  The  time  seems  to  have  arrived  for  a 
reaction  against  these  exaggerations.  In  the  living  being,  just  as 
movement  depends  on  sensation,  so  does  sensation  depend  on  movement. 

In  both  cases  the  nature  of  the  link  is  unknown  to  us  ;  but  none  the 
less  does  this  link  exist,  and  is  in  biology  the  foundation  of  all  that 
distinguishes  it  from  pure  physics. 

Sensibility  and  Organization. — In  the  living  world  sensation  presents 
extremely  varied  degrees,  and  its  development  proceeds  on  a  line  parallel 
with  that  of  the  organization  itself.  It  is  only  strongly  marked  in 
beings  provided  with  the  differentiated  system  known  as  the  nervous 
system ;  it  increases  in  importance  and  elaboration  with  the  progressive 
development  (phylogenetical  and  ontogenetical)  of  this  system.  In 
such  beings,  of  whom  we  ourselves  form  a  class,  a  division  of  attributes 
is  effected  between  the  tissues,  some  of  these  employing  the 
efficient  energies  which  take  part  in  the  execution  of  organic  actions, 
while  another,  the  nervous  tissue,  watches  over  this  employment,  co- 
ordinating and  regulating  it.  This  latter  is  pre-eminently  the  sensory 
tissue,  and  is  in  a  high  degree  both  excitable  and  capable  of  causing 
excitation.  It  is  this  tissue  which  receives  the  stimulation  and  re- 
turns it,  but  transformed  by  the  progress  through  its  paths  ;  and  again 
it  is  this  tissue  which  ensures  the  reciprocal  dependence  and  subordina- 
tion of  the  elements  to  the  whole  and  the  whole  to  the  elements,  and  so 
confers  on  the  organism  its  individuality,  its  unity. 


INNERVATION  3 

Excitability  and  Sensibility. — All  Living  matter  is  excitable  ;  or,  to 
put  it  otherwise,  it  responds  to  actions  directed  against  it,  by  an  expendi- 
ture of  the  special  energy  which  it  constantly  accumulates  internally. 
This  motor  reaction  is  never  hap-hazard,  but— and  this  fact  is  demon- 
strated by  experiment — is  always  directed  with  the  definite  aim  of 
preservation  of  life  in  the  susbtance  stimulated.  Excitability  is  there- 
fore not  merely  a  motor  manifestation,  but  is  duplicated  by  an  internal 
fact  of  rudimentary  consciousness.  It  should  therefore  be  considered  as 
either  a  degraded  form  or  a  first  rough  sketch  of  sensation.  The  elabor- 
ated organization  of  the  superior  animals,  by  giving  to  it  its  highest 
development,  permits  of  our  analysing  the  conditions  of  its  existence  ; 
fundamentally  these  conditions  are  everywhere  the  same ;  they  are 
located  in  the  links  of  reciprocal  dependence  of  the  portions  composing 
the  organism.  The  more  simple  and  homogeneous  is  the  latter,  so 
much  the  more  do  its  reactions  resemble  those  of  ordinary  movement  ^ 
and  so  much  the  farther  are  they  removed  from  those  which  characterize 
genuine  sensibility.  But  in  proportion  as  the  organism  is  complex 
and  differentiated,  so  much  the  more  ^Adll  its  movements  possess  the 
contingent   characteristics   of   sensible   and  intelligent   beings. 

Action  and  Reaction. — In  other  words,  the  living  being  reacts  against 
actions  reaching  it  from  the  external  world,  and  in  so  doing  obeys  a 
general,  universal,  and  indeed  fundamental  law,  one  of  the  first 
inscribed  in  the  physical  code,  a  law,  obedience  to  which  no  living  body 
in  nature  can  escape.  Only,  from  the  fact  of  organization  itself,  tliis 
law  has  assumed  a  new  character,  of  which  it  may  be  said  that  it 
imphes  in  the  living  being  a  remembrance  of  the  past  and  a  prevision 
of  the  future.  The  more  elevated  is  the  organization,  the  more  promi- 
nently does  this  character  stand  forth  ;  on  the  other  hand,  the  nearer 
we  approach  the  purely  physical  elements  entering  as  components 
into  this  organization,  so  much  the  more  is  this  character  effaced, 
nothing  being  left  but  the  simple  reaction  strictly  and  solely  answering 
to  the  action  of  the  present  moment.  Vital  reaction,  practically  so 
different  from  physical  reaction,  proceeds  from  it  by  successive  halting 
places  and  elaborations,  just  as  the  living  being  itself  is  evolved  from 
progressively  organized  crude  matter. 

Division. — The  nerve  tissue  is,  like  all  other  tissues,  originally  formed 
of  cells  ;  but  while  other  cellular  structures  are  usua.lly  merely  composed 
of  duplicated  and  juxtaposed  elements,  it,  thanks  to  the  connexions 
established  between  its  component  parts,  displays  a  genuine  systemi- 
tization.  Its  study  may  therefore  be  carried  on  from  two  different 
points  of  view  ;  one  in  which  the  functions  common  to  all  its  elements 
are  considered  {cellular  functions),  the  other,  in  which  the  functions 

E* 


4  INNERVATION 

special  to  the  groups  or  systems  formed  by  these  elements  are  taken 
into  account  {systematic  junctions).  In  the  study  of  nerve  tissue  the 
distinction  between  these  two  orders  of  functions  is  a  fundamental  one, 
and  the  obscurity  stiU  enveloping  numerous  questions  connected  with 
this  study  is  partly  due  to  the  fact  of  tliis  distinction  being  so 
frequently  ignored. 

The  first  of  these  studies  completes  the  history  of  the  ceUular  functions 
arranged  in  unison  with  the  principal  types  of  living  elements.  The 
second  permits  of  our  penetration  into  the  aggregate  functions  to  which 
the  mutual  association  of  these  elements  gives  rise,  and  it  is  in  the 
nervous  system  that  we  shall  find  the  connexion  where  these  aggrega- 
tions are  brought  into  being  and  their  functions  organized.  The  study  of 
the  nervous  system  is  a  kind  of  nodal  point  in  the  exposition  of  physio- 
logical science. 


PART  I 

Elementary   Nervous   Functions 

The  complexity  of  the  living  being  and  of  its  smallest  organs  is  such 
as  to  compel  us  to  study  them  from  two  points  of  view  :  the  one 
static,  or  that  of  absolute  repose,  that  is  to  say,  death  ;  the  other 
dynamic,  or  that  of  activity,  that  is  to  say.  hfe,  in  its  different  mani- 
festations. Anatomy  is  concerned  with  the  static  condition,  taking 
account,  as  it  does,  of  vital  forms  in  their  fixed  state  ;  the  dynamic 
condition,  or  that  which  physiology  investigates,  is  concerned  with 
movement.  The  two  sciences  are  mutually  related  and  sometimes 
their  special  methods  are  interchanged.  A  summary  review  of  the 
principles  of  the  one  always  aids  in  the  elucidation  of  those  of  the 
other.  By  mutually  borrowing  they  tend  to  reciprocally  fill  up  their 
lacunae. 

1.  Static  Unit. — A  static  unit  of  the  nervous  system  exists  which  is 
commonly  known  by  the  name  of  element :  this  is  the  neuron.  This 
unit  is  of  cellular  order  and  is  indeed  a  symbiosis,  in  the  sense  that  to 
the  fundamental  cell  of  which  it  consists  others  are  added  which  in  a 
way  form  one  structure  with  it.  It  is  an  element  in  the  relative 
sense  of  the  term  only,  because  a  cell  is  a  being  of  complex  organiza- 
tion, but  this  unit  is  very  well  defined  and  thus  acquires  great  import- 
ance. It  is  necessary  therefore  to  briefly  recapitulate  its  most 
essential  characters. 

2.  Dynamic  Unit. — Corresponding  to  this  static  unit  there  exists 
a  dynamic  unit  in  the  same  way  as  for  the  muscular  element,  the 
glandular  element,  etc.  In  the  nerve  this  dynamic  unit  is  less  easily 
recognizable,  because  it  does  not  declare  itself,  as  do  the  preceding 
elements,  through  externally  visible  phenomena  (contraction  secre- 
tion), but  only  by  the  excitability  which  is  more  or  less  the  heritage 
of  every  cell,  or  rather  by  the  reaction  of  this  excitability  on  that  of 
the  other  tissues  which  are  connected  with  the  nerve. 

This  djmamic  unit,  which  we  can  only  describe  by  the  unsatis- 
factory name  of  elementary  nervous  irritability,  is  the  aggregation  of 
the  energies  which  take  their  origin  in  the  neuron,  in  order  to  preserve 
its  existence,  its  composition,  its  structure,  its  internal  and  external 
manifestations,  the  whole  being  co-ordinated  to  a  definite  end. 

5 


6  ELEMENTARY  NERVOUS  FUNCTIONS 

Organization  of  Energy. — Just  as  in  the  nervous  element  the  struc- 
ture is  not  homogeneous,  but  is  made  up  of  comphcated  structures 
which  nevertheless  form  a  coherent  whole,  so  in  this  element,  as  in 
every  cell,  there  is  an  organization  of  energy,  which,  by  the  depen- 
dence which  it  creates  between  its  multiple  forms,  causes  the  latter  to 
take  part  in  the  conservation  of  the  element,  and  guarantees  its  social 
action  in  the  economy.  Like  every  living  individuahty,  the  nervous 
element,  the  neuron,  is  at  the  same  time  both  single  and  multiple, 
and  it  must  not  be  forgotten  that  it  is  so  both  from  the  dynamic  and 
static  point  of  view. 

The  Multiple  Forms  and  Transformations  of  Energy  in  the  Nerve. — 
If  it  be  asked  what  is  the  energy  which  circulates  in  the  nerve,  the 
question  is  badly  expressed,  because  it  suggests  that  one  sole  force 
occupies  its  substance  (as  does  electricity  a  conducting  wire),  and,  a 
priori,  it  is  obvious  that  such  a  comparison  is  inaccurate.  The  utmost 
that  can  be  done  is  to  investigate  the  nature  of  the  final  energy  which 
the  nerve  makes  use  of  at  its  point  of  contact  with  the  muscles,  or  of 
the  organs  which  it  excites.  But  before  arriving  at  this  last  phase, 
it  is  certain — for  proofs  thereof  exist — that  energy  has  undergone  many 
transformations  of  which  we  only  know  those  which  are  the  most 
striking. 


(a)  Chemical  Force. — In  the  nerve,  as  in  every  tissue,  force  is  present  in  its 
chemical  form  ;  because,  as  in  every  other  tissue,  it  is  constantly  produced  by 
exchanges  with  the  blood  through  the  vessels  which  irrigate  it  (gaseous  exchanges 
and  those  of  soluble  substances). 

(6)  Caloric  Force. — In  masses  of  nerve  tissue  of  considerable  size  it  is  now 
admitted  that  there  is  a  slight  disengagerhent  of  heat  ;  because  the  temperature 
of  these  masses  may  be  slightly  higher  than  that  of  the  blood  which  circulates 
in  them  (Mosso). 

(c)  Electric  Force. — In  the  nerve,  as  in  all  the  elements  ha\'ing  a  definite 
orientation,  electro-motor  phenomena  have  been  discovered  which  give  rise 
to  currents  passing  in  a  definite  direction  ;  so  that  a  place  must  be  given  also  to 
electricity  in  the  transformations  of  the  energy  employed  by  the  nervous  element. 
It  is  only  necessary  to  be  aware  that  the  assimilation  of  a  nerve  to  an  ordinary 
electric  conductor  is  radically  inaccvu*ate.  The  conception  of  these  currents  is 
complicated  and  one,  so  to  say,  special  to  the  nerve,  and  their  circulation  probably 
takes  place  in  particles  in  size  approaching  that  of  the  molecule. 

Cycles  of  Energy. — Those  chief  forms  of  force  wliich  arise  by  transfomiation 
the  one  from  the  other  enter  into  cycles  of  energy,  which  sketch  tlie  first  out- 
lines of  that  oi'ganization  of  force  in  the  element,  without  which  all  would  be 
confusion,  and,  thanks  to  which,  order  and  miity  become  paramount  in  it-. 

We  are  but  imperfectly  acquainted  with  the  detail  of  these  cycles  ;  but  every- 
thing shows  that  in  the  nerve  element  (as  in  every  cell)  they  are  numerous, 
giving  rise  to  varieties  and  infinite  gradations.  But  that  which  chiefly  charac- 
terizes them,  in  the  living  being,  is  their  mutual  penetration,  their  superposition. 


THE  NERVOUS  ELEMENT  7 

their  convergence  towards  a  definite  end.  Not  one  is  absolutely  complete  in 
itself  ;  but  each  on  the  contrary  expends  a  part  of  its  force  on  neighbovrring 
cycles,  botli  parallel  and  successive.  Hence  it  is  that  insurmountable  difficulties 
often  arise  in  the  analysis  which  endeavours  to  isolate  them  in  order  more 
accurately  to  study  them. 

Functions. — The  cycles  of  energy  which  are  essentially  simple,  and  are  concerned 
with  the  performance  of  what  we  call  nerve  functions,  are  what  form  the  founda- 
tion of  that  dynamic  nervous  unity  which  our  intelligence  is  not  yet  accustomed 
either  to  see  or  to  investigate,  but  which  in  oijr  science  is  just  as  necessary  as 
the  cellular  conception  (which  is  the  concrete  form  thereof)  is  in  anatomy.  If 
the  details  of  this  organization  of  forces  were  better  known  it  would  lead  us 
without  transition  to  the  knowledge  of  those  complex  acts  which  are  the  functions 
and  which  we  at  present  only  recognize  through  their  results. 

Their  Double  Nature. — These  fvuictions  are  in  a  nervous  element  (as  in  every 
living  element),  of  two  orders  ;  both  make  use  of  the  energy  which  penetrates  the 
nerve  and  quits  it  after  transformation  ;  but  from  it  they  evolve  a  different 
order  of  result.  Some  are  concerned  with  organization  and,  when  once  this 
is  established,  the  conservation  of  the  organization  of  the  neuron  :  for  this 
reason  they  are  called  organotrophic  ;  they  are  internal  to  the  neuron  itself. 
The  others  affect  the  social  aspect  of  the  cellular  individuality  so  far  as  tliis 
concerns  the  total  nervous  system  and  the  individual  itself :  hence  these 
functions  are  those  properly  called  nervous  ;  they  are  external  to  the  neuron, 
and  while  the  first  establish  connexion  between  its  constituent  parts  in  order 
to  preserve  its  static  and  dynamic  identity  in  the  midst  of  perpetual  renewal 
of  its  substance  and  its  energy,  the  second  form  amongst  all  the  neurons  (and  the 
elements  in  connexion  with  the  neuron)  a  systematized  tie  which  gives  unity 
to  the  nervous  system,  and  hence  to  the  individual  of  whom  it  forms  a  part. 

Their  Reciprocal  Dependence. — The  internal  and  external  functions  of  the 
neuron,  both  trophic  and  nervous,  however  well  defined  they  may  be  in  their 
object,  have  necessarily  very  close  mutual  inter-relations.  The  second  are 
clearly  not  possible  luiless  the  first  are  in  existence  ;  the  functional  activity  of 
an  element,  whatever  it  may  be,  presupposes  its  nutrition  :  but  in  their  turn, 
the  first  assume  with  regard  to  the  second  a  more  indirect  dependence,  but  one 
which  is  equally  real  ;    nutrition  languishes  when  function  is  in  abeyance. 


CHAPTER  I 

THE   NERVOUS   ELEMENT 

The  nervous  element  is  the  neuron.  The  neuron  is  essentially  a  cell 
which  is  differentiated  for  the  performance  of  a  special  function, 
that,  namely,  of  innervation  or  of  stimulation  of  other  cellular  elements. 
This  cell  {the  nerve  cell)  is  provided  with  prolongations  (nerve  fibres) 
which  proceed  to  a  greater  or  lesser  distance,  but  have  a  free  termina- 
tion, so  that  the  structure  is  limited  in  a  definite  manner.  To  the 
nerve  cell  thus  furnished  with  its  prolongations  other  structures  are 
superadded,  and  these  are  of  a  more  or  less  cellular  nature  and  origin 
(myelin  sheath,  and  the  sheath  of  Schwann  with  its  nuclei).  It  is 
this  cellular  s?ym620sf 5,  regarded  in  its  totality,  which  forms  the  neuron. 


ELEMENTARY  NERVOUS  FUNCTIONS 

A.— STATIC  CONDITION  OF  THE  NEURON  ;    ANATOMICAL  DATA 


1.  External  Characters  ;  Dimensions. — The  dimensions  of  the  neuron 
are  very  various,  especially  as  regards  length.  Some  are  of  micro- 
scopic dimensions  (for  example,  in  the  retina)  ;  others  may  (in  man) 
attain  and  even  exceed  a  metre  in  length  (for  example,  the  nerves 
of  the  posterior  root,  going  from  the  sole  of  the  foot  to  the  medulla 
oblongata)  ;    between  these  extreme  dimensions  many  intermediate 

lengths  may  be  found. 

Form. — Not  only  the  dimensions,  but 
also  the  shape  of  neurons  may  vary 
extremely.  These  variations  are  in  rela- 
tion, both  the  one  and  the  other,  with 
the  particular  connexions  which  it  is  the 
duty  of  these  elements  to  establish  be- 
tween the  nervous  system  and  the  organs, 
as  also  between  the  different  parts  of  the 
nervous  system  itself.  Nevertheless,  in 
spite  of  this  apparent  diversity,  they  may 
be  brought  back  to  a  common  type  in 
connexion  with  their  most  general  func- 
tion. 

General  Type. — The  neuron  presents  a 
swollen  portion,  which  is  its  cell  of  origin 
(formerly  known  as,  and  still  often  called, 
the  nerve  cell)  from  which  prolongations 
in  different  directions  are  given  off. 
These  prolongations  are  of  two  species  : 
the  first  called  protoplasmic,  ramified  con- 
siderably, without,  however,  anastomosing 
with  one  other  ;  the  second,  thinner  and 
paler,  called  the  prolongation  of  Deiters, 
or  axis  cylinder,  proceeds  to  a  variable 
distance  from  the  cell  origin  and  gives  off 
branches,  partly  on  its  course  {collateral 
branches),  and  partly  at  its  termination 
{terminal  branches).  A  tree  with  its  roots,  its  trunk  and  its  branches 
would  thus  sufficiently  clearly  depict  this  arrangement  if  there  were 
added  to  it  at  the  point  of  expansion  of  the  roots,  a  swollen  portion 
which  would  represent  the  body  of  the  cell. 

Signification  of  the  parts. — From  the  physiological  point  of  view  the 
feltwork  of  the  roots  and  the  foliage  of  this  miniature  tree  give  rise  in 


Fig.  1. — Diagrammatic  represen- 
tation of  an  ordinary  neuron. 

N,  nucleus  of  the  nerve  cell  ; 
Pp,  protoplasmic  prolongations  ; 
Pa,  axis  cylinder  ;  Gm,  sheath  of 
myelin  ;  Sch,  sheath  of  Schwann  ; 
Ea,  annular  node  ;  T,  terminal 
ramifications   of  the   axis  cylinder. 


THE  NERVOUS  ELEMENT 


K4I- 


[^ 


71- 


the  neuron  to  two  parts  which  are  functionally  opposed,  and  which  are 
united  by  the  stem.  The  felt  work  is,  taken  as  a  whole,  an  organ  for 
the  reception  of  impulses  ;  the  branches  would 
form  an  organ  for  the  distribution  or  rearrange- 
ment of  these  same  impulses  to  the  nervous  or 
non-nervous  organs  in  which  they  ramify.  The 
trunk  gathers  them  together  and  transmits  them 
from  one  of  its  extremities  to  the  other.  As  re- 
gards the  cell,  we  shall  endeavour  to  define  the 
part  which  it  plays  a  little  farther  on. 

Synonomy. — In  the  new  terminology  the  pro- 
longations of  the  neuron  formerly  known  as  pro- 
toplasmic are  called  dendrites  ;  the  prolongation 
of  Deiters,  or  the  axis  cylinder,  is  known  as  the 
axon  or  neurite.  The  axon  is  nothing  more  than 
a  nerve  fibre,  of  the  same  kind  as  those  which 
form  the  peripheral  nerves.  Its  essential  portion 
is  the  axis  cylinder,  around  which  are  placed  the 
myelin  sheath,  then  the  sheath  of  Schwann,  with 
its  nuclei  and  its  regularly  arranged  nodes. 

From  its  initial  to  its  terminal  extremity  the 
neuron  thus  presents  three  morphologically  dis- 
tinct parts,  namely  : — 1,  the  dendrites  or  proto- 
plasmic  prolongations ;  2,  the  body  of  the  cell, 
formerly  known  as  the  nerve  cell ;  3,  the  axon  or 
neurite,  which  is  the  axis  cylinder  covered  with 
its  double  protective  sheath. 

,  (a)  Axon. — Ranvier  has  sho\\^l  the  cellular  natui'e  of 
the  envelopes  of  the  axon.  The  myelin  sheath  is  in- 
terrupted from  point  to  point  by  the  nodes  of  the  sheath 
of  Schwann,  which  divide  it  into  regular  segments  (about 
a  millimetre  long  in  ordinary  nerves)  of  which  each  bears 
a  nucleus  in  the  middle  of  its  length.  With  its  myelin 
contents  (phosphorised  fat),  each  segment  would  be  com- 
parable to  a  fat  cell  of  cylindrical  form,  crossed  in  its 
axis  by  the  prolongation  of  the  nerve  cell  which  is 
rightly  known  as  the  axis  cylinder. 

Inasmuch  as  after  death  coloured  or  penetrating  sub- 
stances pass  into  the  axis  cylinder  by  the  nodes,  it  has 
been  thought  that  this  was  the  normal  rovite  for  the 
passage  of  nutritive  material  during  life.  But  this  idea 
is  based  on  an  inexact  appreciation  of  the  nutrition  of 
cells,  as  it  represents  the  cell  as  merely  absorbing  certain 
substances  through  the  most  delicate  portion  of  its  structure.  Absorption,  or, 
to  speak  more  accurately,  the  metabolic  exchange,  is  effected  all  over  the  sur- 
face, as  is  the  case  in  every  cell  whatever.      On  the  other  hand,  these  exchanges 


I 


Fig.  2. — Interannular 
segment  of  the  axon. 
Ca,  axis  cylinder ; 
n,  nucleus  of  the  sheath 
of  Schwann  ;  p,  pro- 
toplasm of  the  same ;: 
e,  node  of  Ranvier. 


10 


ELEMENTARY  NERVOUS  FUNCTIONS 


>p 


imply  successive  and  nvimerous  operations,  n^utations  and  transformations, 
in  whicli  the  cellular  contents  (in  this  case  myelin)  take  a  part  just  as  do  all 
the  rest. 

The  functions  of  the  sheath  of  Schwann  and  of  the  myelin  are  often  considered 
to  be  piirely  mechanical,  or  as  comparable  to  those  of  an  electric  insulating 
substance.  Without  denying  the  part  which  the  myelin  plays  in  this  con- 
nexion, it  is  certain  that  the  jarincipal  functions  of  the  cells  which  envelop  the 

axon  are  not  linaited  to  so  simple  a  role.  These 
functions  have  essentially  for  their  foundation  a 
chemical  evolution,  which  we  can  enounce  in  prin- 
ciple, but  which  our  actual  means  do  not  permit  us 
to  accurately  define. 

Myelinated  and  non-myelinated  fibres. — Near  the 
termination  of  the  axis  cylinder,  the  myelin  ceases  at 
the  level  of  a  last  node,  which  is  called  'preterminal. 
The  axis  cylinder  is  thereafter  bare.  This  portion 
deemed  denuded  is  present  in  all  nerves.  In  the 
nerves  of  the  life  of  relation  it  is  extremely  reduced  ; 
in  the  branches  of  the  great  sympathetic  it  is 
sometimes  of  great  length.  These  non-myelinated 
fibres,  still  called  fibres  of  Remak,  nevertheless  do 
not  form,  as  is  obvious,  a  particular  and  indepen- 
dent species,  but  only  the  continuation  of  the  my- 
elinated fibres. 

In  the  locality  where  it  quits  the  nerve  cell  (pro- 
longation of  Deiters),  the  axis  cylinder  is  equally 
denuded  for  a  certain  length.  The  cell  itself  is 
enclosed  in  a  capsule,  whose  cellular  nature  has  long 
been  recognized.  In  the  spinal  ganglia  of  the  frog, 
yellowish  drops  are  found  in  the  winter  season, 
representing  stores  of  fat  (and  not  of  myelin),  form- 
ing a  season's  reserve,  which  disappears  at  the 
approach  of  smnmer  (Morat).  These  stores  belong 
to  the  cells  of  the  pericellular  capsule  (Bonne). 
Although  of  a  different  natm-e,  they  have  some 
analogy  with  the  myelin  reserve  (this  being  perman- 
ent) of  the  peri-axile  cells  of  the  axon. 

Segmentary  Cells  ;  Their  origin. — The  axis  cylinder, 
which  is  uncovered  at  its  two  extremities,  is  thus 
bare  throughout  the  whole  of  its  length  when  first 
developed.  It  starts  from  the  nerve  cell,  like  a  length- 
ening branch,  until  it  attains  the  organ  for  which 
it  is  destined  (Rouget  and  KoUiker).  Mesenchy- 
matous  cells  (cells  of  conjunctive  nature)  are  ar- 
ranged from  point  to  point  along  its  length,  and 
mould  themselves  on  it  (Vignal).  In  their  mode  of 
appearance  and  their  development  they  follow  the 
same  order  as  does  the  axis  cylinder  in  its  growth  ;  that  is  to  say,  they  extend 
from  the  proximal  to  the  distal  end  of  the  axon.  In  their  interior  they  secrete 
myelin,  and  thus  become  the  segmentary  cells  of  Ranvier.  In  the  extra- 
rachidian,  or  peripheral,  nerves  they  become  invested  with  membranes  which, 
being  continuous,  form  the  sheath  of  Schwann.  In  the  deeply  situated  nerves 
of  the  spinal  cord  and  of  the  brain,  this  sheath  is  wanting,  and  the  myelin  is 
limited  externally  by  the  protoplasm  of  the  investing  cells. 


Pig.  3. — Non-myelinated 
fibres,  or  those  of 
Remak. 

n,  nucleus  ;  p,  proto- 
plasm surrounding  it  ;  b, 
constituent    fibril. 


THE  NERVOUS  ELEMENT 


11 


Collaterals. — The  axon  or  neiirite  exhausts  itself  by  ramifying  in  the  organs, 
nervous  or  other,  to  which  it  transmits  the  impulse  ;  but  in  its  transit  it  fre- 
quently gives  off  fine  fibres,  which  are  very  appropriatelj-  called  collaterals.  It  is 
frequently  the  case  that  these  fibres  are  not  distributed  along  the  length  of  the 
axon  in  a  regular  manner,  but  leave  it  only  when  it  passes  through  some  portion'of 
grey  matter,  as  the  fibres  of  the  great  sjmipathetic  in  the  gangUa,  or  those  of  the 
pyramidal  tract  in  the  pons.  Thus  these  collaterals  belong  to  the  transmitting  polar 
field,  to  which  they  give  a  particular  extension  and  a  special  aspect,  not  coinciding 
with  what  was  formerly  supposed  to  hold  concerning  the  relations  between  the 
nervous  elements.     All  cells  which  are  at  a  great  distance  from  the  nerve  cell 


Fig.  4. — Season's  reserve  of  the  cells  of  the  spinal  ganglia  of  the  frog  in  winter. 
Drops  of  fat,  single  or  multiple,  coloured  by  osmic  acid,  are  seen  in  the  capsule  of  the  cell,'and 
stand  out  more  or  less  prominently  in  its  interior.     In  the  centre  of  the  diagram  a  drop  has  been 


displaced  by  the  manipulations,  and  the  resulting 
drawing  by  Bonne). 


einpty  space  is  seen  in  the  capsule  (froma 


are  considered  as  fulfilling  the  same  function  as  the  strictly  terminal  ramifica- 
tions ;  but  there  are  some  which  take  origin  from  the  axon,  sometimes  at  a 
short  distance  from  the  cell  itself,  almost  at  the  origin  of  this  axon.  There  has 
been  hesitation  in  giving  to  these  collaterals  the  same  signification  as  the  terminal 
branches  of  the  nem-on,  and  many  hypotheses  have  been  brought  forward  con- 
cerning these  singular  formations.  And  at  first  sight  it  seems  indeed  strange 
that  the  nerve  element,  which  has  just  received  the  impulse  by  its  dendrites  in 
some  area  of  grey  substance,  should  there  and  then  distribute  it  to  this  same 
field  before  leaving  it.  But  if  we  reflect  that  in  this  field  itself  associating  cells 
exist  (cells  whose  dimensions  are  relatively  limited,  and  which  do  not  leave  its 
territory),  which  transport  to  it  in  this  way  an  impulse  from  a  short  distance, 
the  fact  will  appear  to  us  less  surprising.  Neurons  of  great  length,  as  the  radicu- 
lar neurons  of  the  antex'ior  horns  of  the  spinal  cord,  alone  combine  the  fmiction 
of  associating  cells  with  that  of  elements  of  projection.  Of  the  impulse  which 
it  has  just  received  from  its  dendrites,  the  nem-on  thus  built  up  yields  a  portion 
to  the  dendrites  of  neighbouring  neurons,  while  it  carries  away  the  remainder  to 


12 


ELEMENTARY  NERVOUS  FUNCTIONS 


a  long  distance.  It  may  be  supposed  on  the  other  hand  that  these  collaterals, 
if  neighbours  of  the  nerve  cell,  perform  the  function  of  dendrites,  and  belong 
to  the  receiving  pole  ;  but  although  up  to  the  present  time  no  method  of  settling 
the  question  experimentally  has  been  discovered,  the  resemblance  of  the  colla- 
terals to  the  terminal  rainifications  makes  us  inclined  to  support  the  first  explana- 
tion ;  the  analogy  of  form,  in  the  absence  of  the  experimental  proof,  prejudices 
in  favour  of  the  analogy  of  function. 

(b)  Body  of  the  Cell. — The  body  of  the  nerve  cell  presents  itself  in  the  form  of  a 
protoplasmic  mass  provided  with  a  large  nucleolated  nucleus.  In  the  interior  of 
this  mass  the  details  of  its  structure  can  be  made  out.  There  may  be  distin- 
guished in  it  a  substance  which  is  known  as  chromatic,  which  can  be  coloured  by 
methylene  blue,  and  a  non-chromatic  substance  which  is  known  as  the  enchyleme. 


CO- 

Fig.  5. — Xerve  tubes  (axons)  of  the 
spinal  cord  without  the  sheath  of 
Schwann. 

mg,  myelin  sheath  ;  g,  peripheral  en- 
velope ;  c,  nucleus  and  protoplasm  observable 
on  the  surface  of  some  slender  nerve  tubes. 


Fig.    6. — Neviroglia    cells    in    a    human 
foetus. 
A,   superficial  cell  of  the  neuroglia  ;    B, 
neuroglia  cell  of  the  grey  matter. 


The  chromatic  substance  is  looked  upon  as  a  sort  of  nutritive  reserve,  distri- 
buted in  the  cell  in  the  form  of  gi'ains,  and  visible  even  at  the  point  of  origin  of 
the  protoplasmic  arborizations.  It  is  this  substance  which  changes  its  appear- 
ance, its  distribution  and  its  quantity,  in  the  principal  conditions  of  the  cell,  as 
the  result  of  long  continued  stimulation  or  after  section  of  the  axon. 

Golgi,  Verrati  and  Nelis  have  demonstrated  in  the  interior  of  the  cell  a  net- 
work which  Avould  seem  indeed  to  be  double,  occurring  in  two  different  planes, 
the  one  intracellular  and  the  other  pericellular.  Bethe,  and  Apathy  have  also 
described  networks  of  this  description  in  the  nerve  cells  of  invertebrates.  The 
connexions  of  these  networks  have  not  yet  been  definitely  determined.  The 
latter  authors  describe  them  as  continuous  with  the  constituent  fibres  of  the 
axon.  On  the  other  hand,  the  body  of  the  cell  (and  not  only  the  dendrites) 
receive  the  contact  of  the  terminal  fibres  of  the  nevirons  which  enter  into  relation 
with  them ;  it  may  be  that  the  pericellular  network  serves  to  establish  these 
relations. 


THE  NERVOUS  ELEMENT 


13 


Cellulipetal  and  Cellulifugal  Prolongations.— The  body  of  the  cell  displays,  in  the 
neuron,  a  locahty  towards  which  the  currents  transporting  the  impulse  tend  to 
converge  and  to  condense  ;    after  this,  according  to  the  direction  of  the  axon, 


Pig,  7. — Short   neuron  of  the  cerebral  cortex  with  its  dendrites   (varicose),  its  axis- 
cylinder  prolongation  (very  fine)  and  the  collaterals  of  the  latter. 
cy,  axis-cylinder  prolongation  and  its  collaterals  ;   t,  terminal  varicose  ramifications  ;  p,  proto- 
plasmic prolongations. 

they  begin  to  start  again,  diverging  by  the  collaterals,  which  take  their  origin 
from  the  axon,  sometimes  but  a  short  distance  from  the  cell.  Ha\dng  respect 
to  the  progress  of  the  impulse,  the  naine  of  cellulipetal  has  been  given  to  the 
converging  prolongations  and  to  the  currents  wliich  they  convey,  and  that  of 
cellulifugal  to  those  which  proceed  from  the  cell,  and  in  tMs  way  diverge.  When 
these  two  terms  are  considered  as  being  equivalent  to  centripetal  and  centrifugal, 
the  ceil  is  compared  to  a  centre  of  association  of  the  neurons  and  of  the  transfor- 
mation of  the  unpulse. 

As  a  matter  of  fact,  the  associ- 
ation really  takes  place  at  the 
reunion  of  the  terixiinations  of 
the  axons  with  the  origin  of  the 
dendrites  ;  the  transformation 
of  the  impulse  can  only  be 
possible  at  the  identical  place 
where  tliis  association  occiirs. 

(c)  Dendrites. — It  would  seem 
that  the  dendrites  are  the  ex- 
tended and  ramified  body  of  the 
cell,  assmning  the  form  of  ar- 
borescent prolongations.  It  is 
only  since  the  apphcation  of  the 
method  of  Golgi  that  their  real 
form  has  been  recognized,  and 
that  it  has  been  possible  to   ex- 


jTiG.   8. — Short  neuron  with  its  two  orders  of  pro- 
longations seen  as  a  whole. 
The  cellulipetal  prolongations  (protoplasmic)  as  well 
as  the  cells  are  in  black  ;  the  cellulifugal  prolongations 
(axon  and  its  collaterals)  are  in  red. 


14 


ELEMENTARY  NERVOUS  FUNCTIONS 


plain  their  extension, 
often  veiy  considerable , 
throughout  the  grey 
matter,  and  even 
sometimes  the  w^hite 
The  peculiar  aj^pear- 
bordering  matter, 
ance  of  these  prolonga- 
tions had  formerly 
caused  them  to  be  con- 
sidered as  possessing 
a  protoplasmic  nature 
analogous  to  that  of  the 
body  of  the  cell,  and  a 
function,  rather  trophic 
than  nervous,  in  the 
exchanges  between  this 
latter  and  its  surround- 
ing medium.  But  their 
function  as  organs 
which  are  receptive  and  conductive  of  the  imiDulse  can  no  longer  be  contested. 
However,  their  functional  is  not  a  -priori  exclusive  of  their  tropliic  role  ;  it  is 
only  necessary  that  tliis  latter  be  effected  in  a  slightly  different  manner  to  that 
which  was  formerly  current.  It  is  scarcely  admissible,  as  Golgi  thought,  that 
these  prolongations  act  as  conducting  channels  of  the  juices  which  they  take  up 
by  their  extremities  in  contact  wdth  vessels  towards  the  cell  ;  but  it  is  credible 
that  the  differentiated  protojjlasm,  the  conductor  of  the  impulses,  which  is 
present  in  them,  is  steeped  (here  as  elsewhere)  in  a  gangue  of  primitive  orchnarily 
troi^Iiic  protoplasm,  wliich,by  its  exchanges  with  the  medium  in  wlaich  it  is 
immersed,  maintains  its  composition  and  its  structure,  and  therefore  its  ner- 
vous function.  Hence  it  may  be  asked  if  the  modifications  of  form  which  ensue 
in  these  prolongations  as  the  result  of  different  conditions  (stimulation,  repose, 
fatigue),  are  anything  more  than  the  changes  correlative  to  the  nutritional 
requirements   of   these   parts. 

The  jSTeuron  and  its  Different  Constituent  Segments. 
{Succession,  Different  and  Synonymous  Forms.) 


Fig.   9. — Dendrites  (protoplasmic  prolongations)  of  a  root 
cell  of  the  anterior  horn  of  the  spinal  cord. 
cy,  its  axis  cylinder  (prolongation  of  Deiters)  proceeds  to  form 
the  axon,  which  extends  the  whole  length  of  the  motor  nerve. 


Prolongation  of  Dei- 

Terminal ar- 

\ 

( 

ters  continued  by 

b  oriza- 

the    axis    cylinder 

tions     (at 

with  its  sheaths  of 

the   extre- 

Nerve cell. 

myelin      and      of 

mity  of  the 

Protoplas- 

Schwann. 

axon. 

mic     pro- 

— 

o 

6 

longations. 

— 

Ph 

"o 

— 

'       00 

^ 

Dendrites. 

Body  of  cell  with 

Axon    or    Neuraxon. 

Collaterals 

>    { 

nucleus  and  nu- 

Mon  axon  (single 

on      the 

m 

■43    \ 

cleolus. 

axon) 

course  of 

1 

Inaxon  (long  axon). 

the  axon. 

— 

Dendraxon     (short 

axon). 

— 

Neurite. 

Diaxon  (double  axon). 
Folyaxon  (multiple 
axon). 

Telodendro- 
non. 

\ 

Schizaxon   (divided 

) 

axon). 

THE  NERVOUS  ELEMENT  15 

2.  Dynamic  Polarization. — By  this  term  is  described  the  functional 
opposition  which  is  attributed  to  the  two  extremities  of  the  neuron. 
When  apphed  to  the  neuron,  the  term  dynamic  polarization  expresses 
a  principle  which  is  established  by  all  experiments  to  which  the  nervous 
system  is  submitted  ;  namely,  that  the  waves  of  the  impulse  which 
pass  through  it  traverse  it  in  a  definite  direction,  which  is  invariable. 
Thus  the  neuron  has  two  poles  ;  the  one  receptive,  whose  duty  it  is  to 
receive  the  impulse  ;  the  other  distributive  or  emissive,  which  transmits 
it  to  other  organs,  or  to  neurons  other  than  itself.  Between  the  two 
poles  is  an  axial  portion,  the  axon,  which  carries  the  impulse  from  one 
pole  to  the  other.  It  is  possible  that  the  axial  part  possesses  the  power 
of  propagating  the  impulse  in  either  direction,  but  the  poles  themselves 
are  incapable  of  inverting  or  exchanging  their  function. 

There  would  be  no  inconvenience,  and  it  would  probably  be  advan- 
tageous, to  describe,  as  Brissaud  has  suggested,  the  receptive  pole  as 
the  positive  pole  and  the  emissive  pole  as  the  negative  pole,  it  being  under- 
stood that  to  these  expressions,  borrowed  from  the  science  of  elec- 
tricity, only  a  comparative  signification,  and  in  no  sense  that  of  iden- 
tity, be  ascribed. 

As  has  been  described  above,  each  of  these  poles  possesses  ramifica- 
tions which  are  frequently  numerous  and  sometimes  very  widely  ex- 
tended. Both  ramify  in  a  territory  or  area  whose  size  varies  and  in 
which  each,  according  to  its  nature,  receives  or  distributes  the  impulse. 

In  a  given  neuron  when  examined  microscopically  it  is  generally 
possible  to  say  which  of  the  two  poles  is  the  subject  of  examination. 
The  receptive  pole  is  that  whose  ramifications  closely  approximate  the 
cell,  so  closely  indeed  that  they  appear  to  originate  in  the  latter.  The 
respective  designation  of  the  poles  is  not  inferred  from  a  structure 
which  would  explain  their  function,  but  is  based  on  experimental 
observations  which  in  a  large  number  of  cases  have  shown  that  the 
propagatio7i  of  the  impulse  proceeds  frotn  the  dendrites  to  the  axon,  and 
passes  through  the  cell  body,  and  not  inversely. 

The  Experimental  basis  of  the  Polarity  of  the  neurons. — The  func- 
tional polarity  of  the  nervous  elements  has  been  proved  to  demonstra- 
tion by  physiology.  It  lays  down  in  principle  that  in  each  of  these 
elements,  possessing  normal  connexions,  the  impulse  is  transmitted  in  a 
definite  direction,  invariably  the  same,  and  that  it  neither  returns  nor 
oscillates,  and  this  physiology  proves  in  a  very  considerable  number 
of  such  cases.  And,  on  its  part,  anatomy  having  succeeded  in  defining 
in  a  number  of  instances  the  structure  and  the  limits  of  these  elements, 
it  has  been  possible  to  establish  certain  relations  between  these  ana- 
tomical data  and  the  direction  of  the  physiological  conduction. 


16 


ELEI^dENTARY  NERVOUS  FUNCTIONS 


Generalization  of  this  datum. — A  neuron  being  given  (or  even  a  recog- 
nizable fraction  of  this  element),  it  is  usually  possible  to  say  in  which 
direction  the  current  of  excitation  is  transmitted  ;  but  there  are  also 
cases  in  which  it  is  impossible  to  predicate  anything  on  this  point. 
This  is  because  the  morphology  of  the  neuron  (form  and  situation  of 
the  cell  and  of  its  prolongation)  is  not  in  any  way  determinate,  but,  on 
the  other  hand,  lends  itself  to  the  thousand  exigencies  which  the  recep- 
tion and  distribution  of  impulses  require  according  to  the  order  and 
the  special  nature  of  these  functions. 

Uncertainty  in  certain  cases. — Whenever  the  neuron  in  which  the 
problem  of  the  direction  of  the  conduction  arises  resembles  those  in 
which  this  direction  has  been  ascertained  by  direct  experiment,  the 
reply  is  relatively  easy  ;  it  becomes  uncertain  whenever  this  criterion 
is  wanting  ;   further,  it  may  be  only  partial,  that  is  to  say,  possible  as 


Fig.    10. — Conriparison  of   the  neurons  of  the  posterior  roots  with  those  of  the~anterior 

roots  (after  M.  Duval). 

CM  and  CG,  their  cells  of  origin,  one  in  the  spinal  cord,  the  other  in  the  .spinal  ganglion  ; 
A,  bare  axis  cylinder  ;  B,  portion  of  the  same  covered  with  a  sheath  of  myelin  without  a  sheath 
of  Schwann  ;  C,  portion  covered  with  a  myelin  sheath  and  sheath  of  Schwann  ;  D,  portion  with 
a  sheath  of  Schwann  without  myelin  ;    E,  bare  terminal  arborizations. 

According  to  Dogiel,  the  cell  CG  of  the  spinal  ganglion  bears  jirotoplasmie  prolongations  or 
dendrites  analogous  (though  less  visible)  to  those  of  the  cell  CM. 


regards  certain  of  the  prolongations  of  the  cell,  and  indeterminate  as 
concerns  other  prolongations. 

Discussion  of  a  particular  case. — One  of  the  most  aberrant  and  most  difficult 
forms  to  classify  in  the  empirical  law  formulated  above,  is  that  of  the  posterior 
radicular  neurons  of  the  spinal  cord.  The  cell  of  each  of  them  is  situated  in  the 
spinal  ganglion  ;  the  axon  is  morphologically  represented  by  the  prolongation 
which  arises  from  it,  and  itself  divides  in  the  form  of  the  letter  X,  to  jaroceed 
on  the  one  side  to  the  spinal  cord,  and  on  the  other,  to  the  cutaneous  investment. 
The  dendrites,  for  a  long  period  ignored,  have  been  discovered  by  Dogiel  :  these 
are  the  prolongations  which  arise  from  the  cell,  and  which  terminate  in  the 
ganglion  Itself,  in  contact  with  terminal  arborizations  belonging  probably  to 
the  great  sympathetic. 


THE  NERVOUS  ELEMENT  17 

If  such  a  neuron  were  obedient  physiologically  to  the  law  of  polarity,  under- 
stood in  its  ordinary  morphological  sense,  it  should  receive  impulses  only  in 
the  ganglion,  and  should  distribute  them  thence  to  the  spinal  cord  and  to  the 
skin  simultaneously. 

And  it  may  even  be  added  that,  if  such  a  neuron  were  met  with  in  any  other 
locality  less  accessible  to  the  isolated  stimulation  of  its  branches,  there  would 
scarcely  be  hesitation  in  attributing  to  it  a  conductive  capacity  in  the  sense 
which  has  just  been  alluded  to.  But  experiment  shows  us  here  that  the  two 
branches  of  the  axon  conduct  the  impulse,  not  merely  as  the  formula  would 
require,  away  from  the  cell  (in  the  cellulifugal  direction),  but  the  one  impulse 
approaches  the  cell  from  the  skin  to  the  ganglion  (cellulipetal),  while  the  other 
proceeds  from  the  cell,  from  the  ganglion  to  the  spinal  cord  (cellulifugal)  in  such  a 
manner  that  it  traverses  the  two  prolongations  placed  end  to  end,  just  as 
would  be  the  case  with  a  single  fibre  proceeding  from  the  skin  to  the  spinal  cord. 

Concerning  the  exact  connexions  of  the  dendrites  and  of  these  remarkable 
neurons,  and  the  nature  of  the  exact  direction  of  their  current  of  excitation, 
experiment  is  silent,  becaiise  it  is  impracticable  under  given  conditions  with  the 
methods  which  are  available  to  us.  It  is  thought,  however,  with  some  prob- 
ability, that  the  principal  current  is  that  which,  proceeding  fron:i  the  organs  of 
touch  situated  in  the  skin,  is  conveyed  in  the  grey  matter  of  the  spinal  cord. 
This  physiological  argument  is  looked  upon  by  some  as  of  such  importance  that 
it  dominates  all  the  others,  and  they  call  "  dendrite  every  celluli])etal  prolonga- 
tion and  axon  every  cellulifugal  prolongation  "  (Van  Gehuchten).  But  then, 
obviously,  these  designations  lose  their  morphological  meaning  in  order  to 
acquire  one  which  is  purely  functional,  and  which  depends  exclusively  upon 
experiment. 

Relative  importance  of  the  different  prolongations  at  different  ages. — It  has 
been  long  known  by  certain  definite  indications,  such  as  relative  size  and  pre- 
cocious development,  that  spinal  ganglia  have,  at  a  certain  period  of  intra-uterine 
life,  an  important  function  which  progressively  diminishes  with  the  develop- 
ment of  the  nervous  system,  and  which  is  relatively  wanting  in  the  adult.  The 
new  anatomical  methods  require  that  embryos  or  young  subjects  be  studied  ; 
it  is  necessary  to  determine  in  the  adult  if  there  exist  intra-ganglionic  con- 
nexions which  can  be  revealed  by  the  use  of  these  methods. 

Adaptation  of  the  Neuron  to  successive  functions. — In  assuming  that  the 
traces  of  these  structures  may  be  definitely  persistent,  the  example  of  the  posterior 
radicular  neurons  shows  us  how  the  functional  evolution  of  a  nerve  elenaent  may 
adapt  its  several  parts  to  functions  altogether  different  to  those  which  are  dis- 
charged by  the  equivalent  parts  of  other  similar  nerve  elements,  to  such  a  degree 
indeed  as  to  invert  the  direction  of  the  conduction  ;  a  new  proof,  if  such  were 
wanting,  that  structure  does  not  predicate  function,  and  that  conclusions  must 
be  drawni  from  the  fii'st  concerning  the  second  only  with  the  gi'eatest  caution. 
The  n^orphological  law  would  appear  to  have  its  own  grounds  different 
from  those  which  initiate  the  physiological  or  functional  law  ;  it  is  not  possible, 
therefore  to  substitute  the  one  for  the  other  by  confusing  them  in  one  common 
statement. 

The  Mixed  Axon,  or  the  Axon  with  a  double  inverse  Conduction. — Avoidance. — 
The  progress  of  the  impulse  in  the  nervous  prolongations,  its  concentration  in  the 
axon,  its  dispersion  in  the  collateral  and  terminal  ramifications,  its  passage  through 
the  body  of  the  cell,  the  manner  in  which  it  enters  or  quits  the  latter,  are  so  many 
questions  which  experinaent  cannot  resolve  in  a  direct  manner,  and  on  which 
only  tentative  opinions  can  be  exjDressed.  As  regards  the  sensitive  radicular 
neurons,  a  cjuestion  of  this  kind  arises  concerning  the  median  prolongation  of 
the  T,  which  laterally  connects  them  with  their  cells  of  origin.     According  to 

P.  C 


ELEMENTARY   NERVOUS   FUNCTIONS 


Cajal,  tlie  impulse  transmitted  from  the  skin  to  the  cord  avoids  this  lateral  pro- 
longation, and  thus  saves  itself  tlie  journey  to  this  cell.  According  to  others 
this  prolongation,  more  voluminous  than  its  two  divisions,  would  represent  the 
association  of  their  fibrils  (Ranvier),  which  are  thus,  in  the  same  axis  cylinder, 
some  cellulipetal,  and  others  cellulifugal.  Thus  a  mixed  axon  would  result,  if 
by  this  qualification  mixed  is  implied  elements  (here  fibrils)  which  possess  the 
facility  of  conduction  in  opjDosite  directions. 

It  is  impossible  to  give  a  decisive  opinion  for  or  against  these  two  modes  of 
regarding  the  question.  For  those  who  maintain  the  possibility  of  the  propaga- 
tion front  one  neuron  to  another  by  simple  contact,  there  would  seem  to  be  no 
impossibility  in  the  passage  of  the  impulses  from  one  to  another  gi'oup  of  fibrils 
in  the  interior  of  an  axon  ;  but  it  must  be  observed  that  the  special  nature  of 
this  so-called  contact  is  unknown  to  us  in  these  two  circumstances,  and  that 
we  are  reasoning  on  resemblances  or  crude  analogies. 
However,  Bethe,  in  experimenting  on  the  crab,  in 
which  these  median  prolongations  have  all  the  same 
orientation,  has  been  able  to  divide  them  with  one 
cut,  and  thus  to  sejiarate  the  cells  of  origin  from  the 
sensitive  fibres  which  appertain  to  them  ;  and  he  has 
observed  that  after  this  separation  cutaneous  stimula- 
tion still  gives  rise  to  reflex  movements,  although  the 
latter  are  weakened. 

The  neuron  ramifies  at  its  two  extremities  ;  it  re- 
ceives impulses  by  numerous  and  sj^aced  jsrolonga- 
tions  ;  it  distributes  them  by  its  branches  which  are 
generally  very  widely  dispei'sed.  On  this  subject  a 
problem  arises  which  we  cannot  resolve,  but  which 
must  not  be  ignored. 

The  impulses  which  the  several  dendrites  receive 
converge  on  the  axon  ;  do  they  mix  in  it,  as  does  the 
blood  in  the  venous  trunks  which  arise  from  the 
capillaries  ?  Or  do  they  follow  parallel  and  indepen- 
dent paths  in  the  axis  cylinder  ?  In  other  words,  do 
the  collaterals,  each  individually,  enter  into  a  deter- 
minate connexion  with  the  dendrites  ;  or  are  they 
all  connected  with  each  dendrite,  and  reciprocally  ?  — 
The  network  which  is  observed  in  the  interior  of  the 
cell,  and  which  is  found  on  the  passage  of  the  den- 
drites to  the  axon  appears  to  furnish  the  re^^ly  to 
this  question.  Whether  this  network  is  limited  to  the 
cell,  or  whether  the  reticulated  arrangement  is  con- 
tinued over  the  whole  extent  of  the  axis  cjdinder,  a  formation  such  as  this  is 
able  to  give  to  the  disti'ibution  of  the  imj^ulses  a  special  character  which  may  be 
described  as  neither  absolute  independence  nor  complete  mixture,  but  a  re- 
arrangement which  obeys  special  laws  and  which  may  vary  according  to  the 
function  of  the  neuron.  The  specific  nature  would  depend  in  a  certain 
measure  upoii  the  latter. 

Objections. — The  theory  of  the  neuron,  on  its  first  appearance,  rapidly  gained 
gi'ound,  not  only  with  neurologists,  but  with  the  whole  scientific  world  ;  and  it 
may  be  said  that  it  has  not,  speaking  generally,  lost  favour,  either  with  the  former 
or  with  tlie  latter.  However,  if  it  has  preserved  its  supporters,  it  has  met  with 
determined  adversaries,  who  do  not  despair  of  finding  it  wanting  in  some  essen- 
tial point.  Their  niost  serious  objection  is  that  the  limitations  of  the  neurons, 
rendered  so  obvious  by  the  chromate  of  silver  method  (isolated  impregnation  of 


Fig.  11. — Cell  of  a  spinal 
ganglion  in  the  rabbit. 

Its  single  prolongation  is. 
united  to  a  fibre  of  the  pos- 
terior root  at  the  level  of  an 
annular  node,  whence  its  T- 
shaped  appearance  ;  E,  node 
of  the  T-shaped  tube ;  N, 
nucleus  of  the  first  segment 
of  the  cellular  branch  of  the 
T  ;  E',  first  node  of  the 
cellular  branch  ;  M,  nuclei 
of    its    capsule. 


THE  NERVOUS  ELEMENT  19 

some  neurons  in  the  middle  of  others),  may  be  an  artificial  result  which  is  due  to 
the  action  of  the  re-agent  employed  ;  thus  has  arisen  once  more  the  discussion 
on  the  continuity  or  the  contiguit>/  of  the  articulated  prolongations  of  these 
neurons. 

It  does  not  enter  into  the  object  of  this  work  to  take  part  in  these  technical 
discussions  :  the  question  wluch  has  thus  arisen,  whatever  may  be  its  impor- 
tance, must  be  fought  out  by  anatomists.  But  it  seems  that,  in  pursuing  tliis 
detail,  the  essential  point  which  this  large  and  admirable  collection  of  observa- 
tions has  so  vividly  brought  out,  the  essential  point  of  view  has  been  lost  sight 
of.  Tliis  point  is  the  individuality  of  the  nerve  element,  of  the  neuron.  For  a 
long  time  this  was  unknown  to  us.  It  was  generally  admitted  that  the  nervous 
system  is  formed  of  two  species  of  elements,  fibres  and  cells,  and  the  point  of 
departure  between  them  was  placed  in  a  locality  where  it  is  clear  that  there 
neither  was,  or  had  been  at  any  period  of  development,  any  discontinuitj*.  We 
now  know  that  in  the  nervous  sj'stem  there  is  no  fibre  which  is  not  the  prolonga- 
tion of  a  nerve  cell,  and  when  this  fibre  passes  from  one  cell  to  anotlier,  we  can 
affii'm  to  which  of  the  two  it  belongs.  Thanks  to  the  new  methods  introduced 
by  Golgi,  the  nerve  element  can  now  be  demonstrated  as  regards  its  general 
structure,  its  exact  boundaries  and  its  principal  details. 

3.  Individuality  of  the  Neuron. — Its  proofs. — The  two  following  facts 
estabhshed,  one  by  embryology,  the  other  by  the  method  of  degenera- 
tion, are  convincing  on  this  most  important  point. 

(1)  The  nervous  elements,  the  neurons,  arise  from  independent  cells  ; 
these  cells,  as  His  has  observed,  give  out  prolongations  in  different 
directions,  in  order  to  be  mutually  connected  and  to  associate  them- 
selves with  the  fixed  elements  of  the  organism. 

(2)  When  the  prolongations  are  separated  from  the  cell  by  section 
they  hecome  the  seat  of  a  degeneration  ichich  terminates  precisely  at  their 
extremity. 

In  leaving  undetermined  the  question  whether  these  prolongations 
have  contracted  connexions  which  establish  their  continuity  by  means 
of  welding,  or  ^^hether  they  remain  in  simple  contact,  these  two  facts 
]3rove  to  demonstration  that  each  nerve  cell,  each  neuron,  has  a  definite 
territory,  instead  of  the  indeterminate  distribution  which  the  hypo- 
thesis of  a  vague  network  connecting  the  cells  formerly  held  to  be  the 
case.  Further,  we  can  recognize  the  limits  of  this  territory.  Hence 
it  follows  that  the  individuality  of  the  nerve  elements  is  no  longer  a 
contestable  matter.  His  has  remarked  that  the  nerve  elements  pro- 
ceed from  cells  definitely  separated  the  one  from  the  other,  and  that 
these  latter  give  rise  to  polar  prolongations  with  free  extremities,  of 
which  one  especially  is  of  long  extension,  in  order  to  form  the  different 
connexions  of  the  nervous  system. 

Ranvier  had  also  seen  that  the  regeneration  of  nerves,  after  section, 
was  effected,  just  as  is  their  origin,  by  a  progressive  budding  of  the 
axis  cyhnder  towards  the  localities  to  be  innervated.  These  facts, 
however,  had  not  attracted  attention,  and  all  the  conclusions  to  which 


20  ELEMENTARY   NERVOUS   FUNCTIONS 

they  point  had  not  been  deduced  from  them.  But  when,  by  Golgi's 
method,  it  was  possible  to  demonstrate  by  preparations  in  which  the 
detail  of  the  prolongation  was  clearly  visible  ;  when,  above  all,  Cajal 
had  given  a  correct  interpretation  of  them,  then  only  a  light  was  thrown 
on  the  subject,  and  the  nerve  element  appeared  in  its  true  limits,  very 
different,  it  must  be  admitted,  from  those  which  Avere  formerly  attri- 
buted to  it.  Whether  these  elements  have  their  ultimate  fibrils  simply 
in  contact,  as  many  believe  ;  or  whether  there  is  between  them  a  con- 
tinuity by  welding,  as  others  maintain,  is  certainly  a  detail  of  import- 
ance, because  in  science  nothing  is  a  matter  of  indifference.  But, 
from  the  special  point  of  view  of  the  individuality  of  the  neuron,  it  is 
a  secondary  question.  The  limits  of  the  latter  are  certainly  as  has 
been  described.  Starting  from  cells  separated,  and  sometimes  widely 
separated  from  one  another,  the  prolongations  which  thus  proceed  to 
meet  each  other  were  in  the  first  instance  necessarily  discontinuous. 
Whether  they  are  free  or  whether  they  are  welded,  they  do  not  cease 
(as  degenerations  show)  to  belong  each  one  to  a  different  cell,  instead 
of  forming  an  indefinite  network  as  was  formerly  supposed. 

In  studying  the  nervous  system  of  invertebrates  bj^  the  aid  of  the  new  colour 
method.  St.  Apathy  and  Al.  Bethe  have  discovered  in  the  neurons  of  these 
animals  a  fibrillary  network  which  is  present  in  the  cell,  and  is  continued  into 
the  prolongations  of  the  latter.  To  this  network  they  ascribe  a  fundamental 
role  in  the  production  of  nervous  phenomena  strictly  so-called,  reserving  to  the 
cytoplasm  of  the  cell  a  purely  trophic  function.  As  a  result  of  these  observa- 
tions, the  theory  of  the  neuron  is  once  again  plunged  into  discussion. 

The  arguments  which  have  been  ch'awn  from  these  observations  are  in  reality 
of  two  kinds,  and  quite  independent  :  the  validity  or  inaccuracy  of  the  one  does 
not  imply  the  validity  or  inaccuracy  of  the  others,  or  reciprocally  ;  hence  it  is 
necessary  to  examine  them  separately.  These  arguments  are  as  follows  : 
( 1 )  The  neurons  being,  so  far  as  regards  their  really  nervous  portions,  formed  of 
fibrils,  if  it  can  be  proved  that  these  fibrils  are  continuous  from  the  one  to  the 
other,  the  individuality  of  the  neurons  must  be  compromised,  and  this  the  more 
because,  in  the  opinion  of  these  authors,  the  connecting  fibrils  interposed  between 
the  cells  would  appear  to  effect  a  sort  of  independence  as  regards  the  latter. 
In  this  way  a  return  would  be  made,  under  a  somewhat  new  aspect,  to  the  old 
division  of  nerve  elements  into  fibres,  on  the  one  hand,  and  cells  on  the  other. 
As  a  matter  of  fact,  neither  of  these  two  authors  clainis  to  have  proved  this  con- 
tinuity of  fibres  from  one  neuron  to  another  ;  it  is  a  supposition  which  appears 
merely  probable  to  them.  The  arguments  given  above  in  favour  of  the  individu- 
ality of  the  neurons  remain  unimpaired.  (2)  The  fibrillary  portion  being  that 
which  is  alone  essential  to  the  performance  of  the  strictly  nervous  functions, 
and  the  cytoplasm  being  reduced  to  a  merely  trophic  function,  the  nerve  cell 
would  no  longer  play  the  preponderant  part  which  has  been  conferred  upon  it  in 
nervous  acts  properly  so  called,  in  physical  functions  for  example.  This  second 
question  is  altogether  independent  of  the  preceding  one  ;  it  concerns  the  internal 
organization  of  the  neuron,  while  the  first  involves  the  organization  of  the  ner- 
vous system  by  the  connexions  established  between  its  elements.  It  is  capable 
of  a  solution  which,  whatever  it  may  be,  predicates  nothing  for  or  against  the 
individuality  of  the  neuron. 


THE   NERVOUS  ELEMENT  21 

Trophic  and  functional  Protoplasm. — In  taking  into  consideration  all  the 
data  of  observation  and  of  experiment  which  are  available  concerning  the  nerve 
element,  I  arrived  at  this  conclusion  ;  viz.,  that  two  portions,  two  different 
protoplasms,  niust  be  distinguished  ;  the  one,  primitive  or  organotro'phic,  is  that 
which  is  visible  in  the  nerve  cell,  in  which  the  nucleus  of  the  latter  is  immersed  ; 
the  other,  junctional  or  nervous  strictly  so  called,  is  that  whose  properties  we 
are  able  to  observe  in  the  axis  cylinder,  when  we  have  separated  this  latter  from 
its  cell  of  origin.  1 

Without  any  doubt  the  plane  of  separation  between  the  two  is  not  marked 
out  by  the  cut  of  the  scalpel,  executed  by  the  experimenter  in  order  to  render 
apparent  either  the  trophic  role  of  the  one  or  the  functional  role  of  the  other. 
This  surface  of  separation  seems  to  be  accurately  defined  in  the  preparations  of 
A  path  J-  and  Bethe. 

Having  thus  localized  (in  the  interior  of  the  neuron)  nutrition  on  the  one 
hand  and  fvmction  on  the  other,  it  is  necessary  to  understand  that  these  pheno- 
mena are  mutually  interdependent,  and  that  the  structures  which  represent 
them  are,  hence,  in  a  constant  condition  of  exchange  and  of  mutual  dependence. 
In  the  neuron,  in  every  cell,  as  in  the  entire  organism,  nutrition  and  function  are 
but  very  distinct  points  of  view  of  an  assemblage  of  functions,  all  of  which  tend 
to  the  same  end  :    the  conservation  of  life. 

4.  Physiological  data. — Before  the  doctrine  of  neurons  had  been 
suggested,  physiology  had  already  furnished  proofs  that  certain  nervous 
elements  terminate  in  a  definite  manner  in  certain  locaUties  which 
experiment  pointed  out.  These  localities  correspond  exactly  to  certain 
of  those  in  which  anatomy  really  establishes  the  points  of  contact 
between  the  neurons,  namely,  •  the  ganglia  of  the  great  sympathetic. 
In  order  of  precedence,  these  are  the  facts  on  which  this  opinion  was 
founded. 

(1)  If  the  chain  of  the  great  sympathetic  be  stimulated  below  the 
first  thoracic  ganglion  (with  reference  to  the  vaso-motor  nerves  pro- 
ceeding to  the  ear),  the  auricular  vessels  contract.  If  this  chain  be 
stimulated  above  this  ganglion,  these  vessels  dilate.  The  dilators  of 
the  auricular  vessels  end  in  these  ganglia  (Dastre  and  Morat). 

(2)  If  the  sympathetic  chain  be  stimulated  either  above  or  below  the 
lumbar  ganglia  (with  reference  to  the  inferior  extremity),  the  hair 
stands  on  end  in  certain  areas  of  the  latter.  But  if  these  ganglia  be 
impregnated  M'ith  a  solution  of  nicotine,  stimulation  applied  below 
continues  to  cause  erection  of  the  hair,  but  when  applied  above  has  no 
effect.  There  is  a  spino-gangliojiic  element  ichich  possesses  the  function 
of  erecting  the  hair  and  ivhicli  terminates  in  the  ganglion  (Langley  and 
Anderson). 

The  specific  nature  of  the  Neurons. — In  accordance  with  the  law  of 
division  of  labour,  which  ^^'e  find  is  applicable  to  the  nervous  system, 
as  to  the  whole  organism,  the  neurons  should  possess  specific  functions. 

1  This  is  clearly  the  idea  which  has  been  i-eproduced  under  slightly  different  names, 
of  distinguishing  in  the  neuron  a  tropho-pJasma  (tropho-protoplasm)  and  a  kineto-plasma 
(functional  or  nervous  protoplasm  strictly  so-called). 


22  ELEMENTARY    NERVOUS   FUNCTIONS 

It  was  at  first  thought  that  this  specific  action  was  connected  with 
certain  external  morphological  characters  of  the  neurons,  that,  for 
example,  all  those  which  experiment  proves  to  be  sensory  would  corre- 
spond to  a  definite,  externally  recognizable,  type  ;  all  those  which  are 
known  as  motor,  to  an  equally  definite  type,  but  differing  from  the 
preceding  one,  etc.  .  .  .  This  induction  has  not  been  verified.  The 
study  of  morphological  characters,  in  proportion  as  it  is  carried  out 
by  the  aid  of  more  perfect  methods,  has  rather  tended  to  collect  to- 
gether the  neurons  discharging  all  functions  under  a  common  type, 
recognizable  among  a  great  variety  of  forms,  but  of  which  not  one 
corresponds  to  any  function  with  which  we  are  acquainted. 

This  rebuff  is  due  to  the  fact  that  the  reasoning  on  which  these  obser- 
vations were  based  was  fundamentally  erroneous.  The  functions,  of 
which  up  to  the  present  time  the  connexion  with  the  individual  form 
of  nerve  elements  has  been  investigated,  are  not  localized  in  these 
elements,  but  in  the  systematized  groups  of  which  they  form  a  part, 
and  whose  function  they  regulate  in  a  certain  manner.  By  itself  the 
neuron  is  incapable  of  causing  either  movement  or  sensation,  far  less 
ideation  ;  but  it  originates  these  several  functions  in  the  organs  or 
the  complex  systems  with  which  it  is  itself  united.  In  other  words, 
motion,  sensation,  ideation  are  not  cellular  functions,  but  systematic 
functions.  They  are  not  simple  facts,  but  synthetic  expressions  imply- 
ing the  co-operation  of  a  large  number  of  elements,  whose  individual 
function  is  not  perceptible  in  the  perfected  whole.  The  existence  of 
specific  systems,  corresponding  to  specific  functions,  nevertheless 
postulates  that  the  order  of  their  elements  is  different  in  each  of  them. 
There  is  then,  on  passing  from  one  system  to  another,  a  specificity  of 
connexion  amongst  those  elements  which  causes  one  to  react  in  a 
different  fashion  from  the  other.  Finally,  a  system,  considered  apart, 
is  not  the  indefinite  reproduction  of  the  same  element,  but  necessarily 
consists  in  an  aggregation  of  parts  or  of  differentiated  elements,  with- 
out which  its  function  would  be  merely  that  of  this  element,  magnified 
indeed  or  multiplied,  but  without  other  alteration.  It  must  be  then 
that  the  nervous  elements  present  a  certain  individual  specificity,  in 
the  aggregations  which  they  form  ;  but  this  specificity  must  be  sought 
for  in  other  ways  and  on  other  foundations. 

The  fact  of  the  name  of  system  being  sometimes  applied  to  cell  groups 
which  are  in  reality  in  no  sense  systematized,  has  contributed  to  bring 
about  this  change.  The  muscular  structure,  for  example,  consists 
merely  in  the  repetition  of  a  great  number  of  elements,  whose  cellular 
function  is  obvious  (irritability  manifesting  itself  by  the  definite  con- 
traction of  its  protoplasm)  ;  by  itself  it  is  not  a  sj^stem,  but  its  elements. 


THE  NERVOUS  ELEMENT  23 

mutually  attached  and  connected  with  the  organs  of  sense  by  nervous 
elements,  make  up  functional  systems  which  are  more  or  less  complex, 
such  as  that  of  respiration,  of  phonation,  of  speech.  In  systems  thus 
built  up,  the  initial  elements  (organs  of  sense)  and  terminal  elements 
(muscles),  have  very  obvious  cellular  functions,  while  those  of  the 
intermediate  elements  (nervous)  elude  direct  analysis.  Hence  the 
cellular  function  of  the  muscles  has  often  been  transferred  to  the  ner- 
vous system  (motricity),  and  hence  also  the  total  function  of  this  system 
(sensation)  has  been  compared  to  a  cellular  function  of  its  elements. 
These  inaccuracies  in  the  use  of  terms  must  be  rectified,  otherwise 
error  and  confusion  will  result. 

Varied  forms. — A  large  number  of  nem-ons  appear  at  tlie  first  glance  to  depart 
widely  from  the  general  type  described  above  ;  it  is  possible,  however,  to  bring 
them  back  to  it  without  much  difficiilty.  The  body  of  the  cell  is  not  necessarily 
situated  in  the  vicinity  of  the  receptive  pole,  but  may  occur  also  in  the  course  of 
the  axon,  as  in  the  ganglia  of  the  acoustic  nerve.  Further,  certain  cells  (for 
example  those  of  the  spinal  ganglia)  are  called  unipolar  because  they  give  off 
but  a  single  prolongation  ;  but  it  is  known  that  this  single  prolongation  bifvircates 
like  the  transverse  branch  of  a  T,  in  order  to  send  a  fibre  to  the  skin  and  another 
to  the  spinal  cord,  both  terminating  by  ramifications,  in  such  a  way  that  the 
two  poles  can  be  found  there  without  difficulty.  The  reason  of  this  singular 
arrangement  is  not  knoAAOi  to  us,  and  the  function  of  the  median  prolongation 
to  which  the  cell  is  suspended  is  equally  obscm'e.  It  is  possible  that  the  impulse 
avoids  it  wholly  or  partially,  as  Cajal  maintains  ;  it  is  possible  that  an  inverse 
double  root  may  exist  in  this  prolongation,  which  assures  its  circulation  in  the 
cell,  as  Renaut  holds. 

In  certain  neurons  the  axon,  instead  of  being  single,  verj^  soon  divides  into 
two  branches,  which  sometimes  follow  different  directions  for  a  gi-eat  distance  and 
sometimes  even  ]iroceed  in  opposite  directions. 

Amacrine  Cells. — Certain  cells  which  are  entij-ely  embedded  in  the  grey  mat- 
ter, or  in  the  membranes  which  recall  its  structure,  as  the  retina,  are  furnished 
with  numerous  arborescent  prolongations,  amongst  which  none  is  detectable 
which  morphologically  represents  an  axis  cylinder  or  axon.  It  would  not  be 
right  to  maintain  from  such  an  arrangement  that  in  these  elements  the  direction 
of  condviction  is  a  matter  of  indifference  :  it  can  only  be  said  that  this  direction 
is  imknown  to  us.  In  none  of  the  localities  in  which  it  is  available,  does  physio- 
logical experiment,  made  in  situ,  prove  the  existence  of  any  instance  of  indefinite 
conduction  ;  but,  on  the  contrary,  this  latter  appears  to  be  everj^where  effected 
in  a  perfectly  definite  manner. 

Nervous  Amoeboism.- — The  mode  of  termination  of  the  nervous  j^rolongations, 
whether  free  or  fixed,  is  connected  with  a  problem  different  from  that  of  the 
individuality  of  the  neuron.  If  tlie  neurons  are  fixed  tliey  are  necessarily 
mechanically  immobile  ;  if  they  are  free  from  attachment  they  are  capable  of 
receding  and  approaching  one  another  under  certain  conditions  which  are  not 
yet  ascertained.  Rabl-Ruckard.  Lepine,  Tanzi,  M.  Duval  have  appealed 
to  displacements  of  this  character  in  order  to  explain  the  dissociations,  variations 
and  functional  paralyses  which  are  observed  in  healtli  and  in  certain  maladies. 

To  these  supposed  movements  M.  Duval  has  given  the  name  of  nervous 
amoeboism,  a  very  definite  expression,  but  one  which,  by  comparing  the  extremely 
differentiated  prolongations  of  the  nerve  cell  to  the  pseudo-podia  of  an  amoeba. 


24  ELEMENTARY   NERVOUS   FUNCTIONS 

clearly  goes  far  bej^ond  his  meaning.     As  a  matter  of  fact,  do  movements  of  this 
kind  (analogous  to  muscular  contraction)  take  place  in  the  nerve  terminations  ? 


Fig.    12. — Different  types  of  nerve  cells  coloured  by  the  rapid  method  of  Golgi. 

A,  nerve  cell  of  the  superior  cervical  ganglion  of  a  human  embryo  of  25  centimetres  (after 
Van  Gehuchten). 

B,  cell  of  the  molecular  layer  of  the  cerebral  cortex  in  a  rabbit  aged  eight  days  (after  Ramon  y 
Cajal)  :  cy,  polar  or  principal  axis  cylinders  ;  a,  supernumerary  axis  cylinders  starting  from 
different  protoplasmic  branches  ;    h,  ramifications  of  tlie  axis  cylinders. 

C,  cell  of  Purkinje,  from  the  cerebellar  cortex  of  a  cat  aged  fifteen  days  (after  Ramon  y  Cajal). 

D,  large  pyramidal  cell  of  the  cerebral  cortex  of  a  mouse  aged  one  month  (after  Ramon  y 
Cajal)  ;   Pp,  peripheral  spiny  protoplasmic  prolongation. 

E,  two  root  cells  of  the  anterior  horns  of  the  spinal  cord  of  a  fowl  at  the  eiglith  day  of  incubation 
(after  Van  Gehuchten). 

In  all  the  diagrams,  cy  indicates  the  axis-cylinder  prolongation. 


THE   NERVOUS    ELEMENT 


25 


Changes  of  form  in  the  Dendrites. — Demoor,  Stefanovvska  and  Manouelian 
claim  to  have  demonstrated  that,  independently  of  the  slow  movements  of 
growth  of  the  prolongations  during  their  development,  there  are  other  extem- 
poraneous movements,  which  give  to  these  prolongations  variable  appearances 
and  dimensions,  following  two  conditions,  the  one  of  activity,  and  the  other  of 
repose.  In  examining  the  dendrites  of  the  cells  in  the  brains  of  animals  killed  in 
these  two  conditions,  these  authors  have  found  that  they  differ  in  the  following 
points. 

In  the  one  case  these  dendrites  bear  at  their  extremities  and  laterally  pyriform 
prolongations  ;  these  are  met  with  in  brains  investigated  in  their  normally 
active  condition  ;  in  the  other  case  tliese  prolongations  have  disappeared  into 
the  trunk  which  supports  them,  which  has  assumed  a  varicose  aspect  in  conse- 


FiG.   13. — Pyramidal  cells  of  the  marmot  in  two  different  conditions  (after  Querton) 
On  the  left,  pyramidal  cell  of  the  marmot  awake  ;   on  the  right,  that  of  the  marmot  asleep. 


quence  of  their  absorption  :  this  condition  is  met  with  in  morphia  poisoning, 
anaesthetic  sleep,  and  sleej)  succeeding  prolonged  fatigue,  itself  the  result  of 
violent  stimulation. 

The  preceding  authors  are  unanimous  in  regarding  these  changes  of  form  as 
explaining  the  two  conditions,  the  one  of  functional  activity,  the  other  of  abeyance 
of  function,  of  nervous  groups  :  the  first  of  these  two  conditions  being  rendered 
possible  by  the  establishment  of  connexions  between  the  elements  which  help 
to  make  up  a  system,  the  second  resulting  from  a  temporarj^  rupture  of  these 
connexions. — Whether  these  changes  are  definitely  connected  with  special 
states  of  the  nervous  system,  may  be  decided  by  experiment  ;  but  that  they 
explain  these  conditions,  is  niore  difiticult  to  adnut.  Kolliker  has  brought 
forward  the  following  argunaents  against  nervous  amoeboisra  :  the  axis  cylinder 
on  which  we  are  able  to  experiment  is  not  contractile  ;  the  nervous  prolongations 


26  ELEMENTARY   NERVOUS   FUNCTIONS 

wliich  can  be  followed  into  the  tissues  in  transparent  animals  show  no  visible 
movement. 

Functional  dissociation  ;  Mechanism  and  localization.— Concerning  the  exis- 
tence of  a  nervous  amceboism  projierly  so  called,  we  have  just  made  express 
reserves  which  are  rendered  necessary,  we  consider,  by  the  want  of  precise  infor- 
mation regarding  the  functional  mechanism  of  the  neuron,  and  the  difficulty  of 
attributing  a  causal  signification  to  the  anatomical  and  experimental  facts  by 
which  it  has  been  attempted  to  explain  this  mechanism.  Having  made  these 
reservations,  we  consider,  nevertheless,  that  the  fundamental  idea  on  which 
this  conception  is  based  deserves  to  be  weighed,  and  that  there  is  something  in  it 
which  is  worthy  of  discussion.     It  is  this  idea  which  it  is  now  necessary  to  evolve. 

The  study  of  the  nervous  system  displays  it  to  us  as  presenting  during  its 
functional  activity,  dissociations  and  associations  of  its  different  parts,  which 
are  sometimes  isolated  the  one  from  the  other,  sometimes  united, 
according  to  the  natiare  or  the  complexity  of  the  act  to  be  accom- 
plished. It  being  admitted  as  proved  that  such  separations  and  recon- 
nexions  arise  in  tlie  nervous  system,  it  is  natural  to  suppose  that  a  rupture  and  a 
renewal  of  the  connexions  between  its  several  parts  should  be  effected,  especi- 
ally in  that  locality  where  its  elements  (nerve  cells),  in  giving  off  their  opposed 
prolongations,  have  first  encountered  each  other  in  the  course  of  their  develop- 
ment in  order  to  build  up  the  system  in  its  totality  and  the  sub-systems  which 
compose  it. — Thus,  in  so  far  as  these  phenomena  of  dissociation  and  association 
are  localized  at  the  extremity  of  the  neurons  (at  their  points  of  contact),  which 
the  study  of  nervous  functions  renders  apparent,  no  risk  of  self-deception  arises, 
whatever  may  be  the  modifications  or  the  facts  which  the  future  may  reveal  as 
necessary  to  our  p)resent  conceptiors  with  regard  to  the  constitution  of  the 
nerve  element.  It  seems,  indeed,  that  it  is  here  (at  the  point  of  junction  of  the 
neurons)  that  the  principal  transformations  which  the  impulse  undergoes  in 
passing  through  the  grey  matter  take  place.  Fundamentally,  what  is  generally 
described  as  a  centre  is  merely  a  locality  tvhere  the  neurons  are  able  to  organize 
themselves  into  a  definite  system  (partial)  in  order  to  perform  a  definite  function. 

But  to  this  problem  of  iGcalisation  another  is  added,  concerning  the  intimate 
mechanism  of  the  transformation  brought  about  in  the  grey  matter  every  time 
that  its  organization  adapts  itself  to  the  performance  of  a  si^ecial  act.  Do  the 
breaks  and  the  union  between  neurons  consist  in  mechanical  and  visible 
displacement,  or  in  molecular  movements  which  our  optical  appliances  do  not 
permit  us  to  recognize  ?  At  the  present  time  it  is  impossible  to  express  a  definite 
opinion  on  tliis  C|uestion.  Dissociations  and  associations  between  nerve 
elements  certainly  exist  ;  in  all  probability  they  may  be  localized  in  the  grey 
matter  at  the  points  of  junction  of  the  nerve  elements.  No  definite  state- 
ment can  be  made  concerning  the  mechanism  by  which  they  are  carried  out. 

Nevertheless,  as  mechanical  phenomena  properly  so  called  are  those  which 
are  most  easily  comprehended,  as  they  are  those  which,  in  the  study  of  every 
function  have  always  contributed  to  furnish  the  first  intelligible  ideas,  the 
doctrine  of  amceboism,  by  clearly  defining  the  question  of  the  connexions 
between  nerve  elements,  indicates  progress  in  the  study  of  nervous  physiology. 
From  another  point  of  view,  it  has  led  to  the  production  of  works  and  to  the 
determination  of  facts  which,  however  obscure  their  signification  may  be  at  the 
present  time,  are  yet  of  great  interest. 

Connexions  of  the  Neurons. — The  individuality  of  the  neurons  is  proved  ; 
it  is  founded  on  the  idea  of  their  exact  limitation  and  of  their  independent  life. 
It  remains  to  ascertain  the  mode  of  connexion  which  exists  between  them  and 
the  other  tissues.  On  this  point  it  may  be  said  that  scarcely  anything  is  known. 
Whether  in  the  purely  static  condition,  or  whether  in  the  dynamic  condition, 
the  data  we  possess  concerning  these  connexions  are  very  incomplete. 


THE  NERVOUS  ELEMENT  27 

The  terminal  and  collateral  arborizations  of  certain  neurons  come  into  con- 
tact with  the  initial  arborizations  or  dendrites  of  other  neurons.  The  collaterals 
and  terminals  of  the  neuron  form  no  connexion  amongst  themselves,  any  more  than 
do  the  dendrites.  Such  is  at  least  the 
view  generally  maintained.  Xever- 
theless,  Renaut,  studying  the  retina  by 
means  of  methylene  blue,  has  some- 
times observed  two  cells  luiited  by  a 
large  protoplasmic  expansion  ;  each 
one  has  its  dendrites,  one  only  gives 
off  an  axis  cylinder  ;  he  calls  these  Fig.  14. — Termination  of  neiu-ons  in  the 
twin  neurons^    On  other  occasions  two  secretory  elements  of  glands, 

neighbouring    cells,      possessing     their  A,  cell  of  the  parotid  gland  in  the  rabbit  ; 

axis  cylinders  and    protoplasmic  pro-       B,  cell  of  the  mammary  gland  of  a  cat  during 
•^  -11  i-     1  gestation. — The    ternimations    have    no    con- 

longations,   are  united  by  one  of  these      nexion  with  the  nuclei  of  the  cells,  but  only 
prolongations  ;     these  he  calls  coupled       with  their  differentiated  protoplasm. 
neurons. 

Adhesive  supports. — Even  by  leaving  aside  these  exceptions  to  the  general 
law,  it  is  very  difficult  to  gather  together  the  connexions  between  nem'ons  in  a 
single  formula.  Contact  of  the  collaterals  and  terminals  occiu"S,  not  only  as 
regards  the  dendrites,  but  also  often  with  the  body  of  the  cell  which  receives 
the  transmitted  impulse.  On  the  other  hand,  this  contact  is  effected  not  only 
by  the  extremities  of  these  prolongations  (axial  or  protoplasmic  cylinders) 
between  themselves,  but  also  for  a  certain  extent  of  their  length.  The  two  orders 
of  prolongations  form  networks  and  felting,  which  render  it  possible  for  the 
same  order  to  enter  into  contact  witli  several  others,  or  several  times  with  the 
same.  These  are  the  multiplied  contacts  which  Renaut  terms  adhesive  supports. 
Observing,  on  the  other  hand,  that  the  protoplasmic  prolongations  present, 
under  certain  conditions,  a  headed  aspect  which  he  regards  as  connected  wdth  the 
state  of  activity  of  the  neurons,  this  author  explains,  by  the  apj^earance  and 
disappearance  of  this  beaded  state,  the  occurrence  of  these  adhesive  supports, 
which  enable  the  transmission  of  the  impulse  from  one  neuron  to  another  to  be 
effected. 

It  is  umiecessary  to  fm-ther  criticise  these  explanations  and  other  similar  ones, 
each  of  which  is  based  indeed  on  some  special  anatomical  fact,  but  whicli,  in  its 
totality  and  according  to  the  admission  of  its  author,  remains  hypothetical. 
Apart  from  the  fact  that  the  impulse  is  transmitted  from  one  nem-on  to  another 
in  a  definite  direction,  we  are  almost  entirely  in  a  state  of  ignorance  witli  regard 
to  this  matter.  We  know  neither  tlie  nature  of  the  transmitted  movement, 
nor  the  niedium  in  which  it  is  transmitted,  nor  the  conditions  of  its  transmission. 
We  can,  it  is  true,  detect  after  death  changes  of  form  corresponding  to  such  or 
such  a  condition  which  we  have  induced  in  the  animal  during  its  life  ;  but  we 
must  remember  that  the  movements  of  cellular  protoplasm  are  of  diverse  nature, 
in  connexion  with  the  different  functions  of  the  life  of  the  cells  ;  there  is  no 
guarantee  that  the  changes  thus  observed  are  of  a  pvu-ely  functional  nature, 
the  modality  of  the  function  being  itself  unkno^^^l  to  us. 

Under  the  influence  of  the  impulses  which  are  communicated  to  it,  the  pro- 
toplasm of  the  body  of  the  nerve  cell  experiences  analogous  changes  of  form,  of 
volume,  of  coloration,  or  of  the  situation  of  its  parts,  which  may  be  considered 
as  being  of  a  trophic  rather  than  of  a  functional  natiu-e. 

Mitral  Cells  of  the  Olfactory  Lobe. — The  cells  of  the  olfactory  lobe  are  disposed 
in  a  typical  manner,  which  is  of  great  value  as  regards  the  interpretation  of  the 
connexions  between  neiu'ons.  Eacli  one  of  these  cells  has  a  special  cellulipetal 
prolongation  whose   dendritic  arborizations  are  (in  the  glomerulus)  comiected 


28 


ELEMENTARY   NERVOUS   FUNCTIONS 


with  the  terminal  arborizations  of  the  axons  of  the  nem'ons  proceeding  from  the 
sensorial  portion  of  the  nasal  mucous  membrane.  In  the  opposite  direction  it 
gives  off  a  cellulifugal  prolongation,  which  is  an  axon  proceeding  in  the  direction 
of  the  brain.  Lastly,  these  cells  emit  lateral  prolongations,  arranged  at  I'ight 
angles  to  the  preceding  ;  these  last  are  connected,  either  directly  or  by  associat- 
ing cells,  with  the  terminal  ramifications  of  the  axons  of  the  centrifugal  elenients 
which  are  contained  in  the  olfactory  tract,  centrifugal  elements  which  are  met 
with  again  in  the  optic  nerve  and  other  analogous  sensory  structvires. 
'  The  excitations  of  different  origin  arrive  therefore  at  the  nem-on,  thus  built 
up,  by   different  routes  ;    none  of  the  elements  which  are  in  connexion  with  it 


Fig.    1.5. — Connexions  of  peripheral  neurons  with  the  deep  neurons  in  the  olfactory 
system,  at  the  level  of  the  glomeruli  of  the  olfactory  bulb. 

The    mitral  cell  receives  the  impulse  in  the  glomerulus  by  an  elongated  prolongation  which 
ramifies  in  it.     The  glomerulus  is  a  functional  nervous  centre. 


directly  touches  its  cell.  This  is  a  proof  that  this  contact  witli  the  cell  is 
in  no  sense  necessary,  and  that  the  impulse  is  received  by  special  apparatus 
adapted  to  the  purpose. 

Pericellular  Baskets. — However,  there  are  a  considerable  number  of  cases 
where  the  connexions  between  neuron  and  neuron  are  effected  by  the  contact 
of  the  terminal  ramifications  of  the  one  with  the  body  of  the  cell  of  the  other. 
It  is  clear  that  there  is  here,  under  these  apparent  diversities,  a  general  arrange- 
ment which  enables  them  to  be  collected  together  under  a  common  rule.  The 
body  of  the  cell,  more  than  the  nvicleus  and  the  other  parts  which  make  it  what 
it  is,  contains  the  expansion  of  the  fibrils  which,  in  all  the  other  portions  of  the 
neuron  (dendrites,  axon,  collaterals  and  terminals),  convey  the  impulse.  When 
the  cell  is  on  the  course  of  the  neuron,  it  is  simply  passed  through  by  this  latter ; 
when  it  is  at  its  origin,  in  such  a  way  as  to  itself  form  its  receptive  pole,  it 
necessarily  contains  the  initial  extremities  of  these  fibres,  which  renders  them 
capable  of  gathering  together  the  impvilses,  when  it  is,  as  often  happens,  placed 
on  a  chief  point  of  bifurcation,  or  of  the  ramifications  of  prolongations,  the 
fibres  which  pass  through  it    adapt    themselves    to    this   distribution,  varying 


THE  NERVOUS  ELEMENT 


29 


according  to  the  circumstances  of  the  impulse.  It  is  clearly  the  fibrillary  part 
which,  in  each  one  of  these  cases,  assumes  the  performance  of  the  fimction 
which  is  demanded  of  it  according  to  its  situation. 


Fig.    16. — Elements  of  the  cortical  matter  of  the  cerebellum  amongst  which  is  a  basket 

cell  (M.  Duval). 

CC,  basket  cells  ;  CP,  pj-ramidal  cell  ;  co,  several  baskets  ;  cp,  the  basket  cell  supported  by 
the  pyramidal  cell. 

Spiral  fibre  ;  Its  signification. — Tn  the  batrachia  are  found,  in  the  ganglia  of 
the  great  s;y'Tnpathetic,  pyriform  pedunculated  cells  on  an  axon  which  turns 
towards  the  periphery  ;  around  this  pedicle,  as  round  an  axis,  is  rolled  a  fibre 
called  spiral,  of  w^hich  the  connexions  with  the  cell  are  noticeable.  This  fibre 
is  the  terminal  prolongation  of  another  neuron  whose  cell  is  situated  higher  up, 
and  which  has  just  come  in  contact,  by  its  ultimate  ramifications,  with  the  pyri- 
form cell,  tlirough  a  varicose  pericellular  network  situated  between  the  cajisvile 
and  the  nervous  protoplasm  (Xicolajew). 


B.     DYNAMIC  CONDITION  :    FUNCTIONS  OF  THE  NEURON 

Each  system,  individual  cell,  or  organized  group,  necessarily  pos- 
sesses two  orders  of  functions  :  the  one  internal  to  the  system  itself, 
for  the  conservation  of  this  system  (or  its  development  if  it  is  in  process 
of  organization  and  of  growth)  ;  the  other  having  an  influence  at  the 
exterior  of  the  system,  and  which  connects  it  with  its  surrounding 
medium,  or  with  a  more  complex  system  of  which  it  forms  part.  Bio- 
logically, the  first  are  commonly  called  trophic  functions,  that  is  to  say, 
those  of  conservation  or  nutrition  ;  while  the  second  are  known  as  social. 


30 


ELEMENTARY   NERVOUS    FUNCTIONS 


Tig.    17. — Cells  furnished  with  a  spiral  fibre  in  the 
frog. 

On  the  left  is  seen  the  origin  of  the  spiral  fibre  in  a 
fine  pericellular  network. 


that  is  to  say,  those  func- 
tions which  are  related  to 
cell  elejnents  of  more  or 
less  equivalent  value. 

I.  Functions  of  Internal  or 
Trophic  Connexion 

The  neuron  is  a  living 
unity  ;    but  this  unity  is 
made  up  by  the  associa- 
tion   of     complex    parts, 
maintained  in  a  condition 
of  mutual  dependence,  by 
which  its  conservation  is 
assured.     These    ties    be- 
tween      its      component 
parts  represent  the  func- 
tions which    are    internal 
to  the  neuron  itself,  and   which,   in  order  to  conform  to    the  cus- 
tomary   mode    of    expression,    w^e    shall     describe    as     trophic    or 
organo-troiJihic. 

When,  by  any  means  whatever,  we  break  these  ties,  disorder  reigns 
rampant  in  this  co-ordinated  whole  ;  the  equilibrium  which  main- 
tained its  form  and  its  existence  is  destroyed  ;  this  form  and  this  exist- 
ence are  both  simultaneously  compromised  ;  the  element,  to  adopt 
the  usual  expression,  degenerates.  This  degeneration  may  entail  its 
total  or  partial  death  ;  in  this  latter  case,  when  its  essential  portions 
escape  destruction,  reconstruction  commences  in  order  to  restore  the 
form  of  the  neuron  as  well  as  its  dimensions  and  its  primitive  integrity  : 
this  is  regeneration. 

At  least  three  forms  of  degeneration  are  distinguished,  viz.  :  Wallerien 
or  descending  degeneration  ;  ascending  degeneration  ;  atrophic  degen- 
eration or  that  resulting  from  loss  of  function.  All  these  varieties 
have  this  in  common,  that  a  local  limited  lesion,  produces  alterations 
which  are  propagated  to  a  distance  in  the  nerve  element  or  in  another 
element  consecutive  to  it,  but  each  form  of  degeneration  is  met  with 
in  determinate  conditions. 

1.  Wallerien  or  Descending  Degeneration. — Fontana  had  already 
remarked  that  section  of  a  nerve  is  followed,  after  some  days,  by  the 
loss  of  its  excitability,  but  to  Waller  is  due  the  discovery  of  the  laws 
which  regulate  the  degeneration  in  its  most  typical  and  common  form. 


THE  NERVOUS  ELEMENT 


31 


descending  degeneration,  which  nov>'  bears  his  name.     The  following 
are  the  conditions  of  its  j)roduction. 

Experiment. — Let  the  anterior  and  posterior  roots  of  a  pair  of  spinal 
nerves  in  an  animal  be  cut  simultaneously^,  and  after  some  days  exam- 
ined from  the  point  of  view  both  of  their  excitability  and  of  their 
modifications  of  apjDearance  and  of  structure  ;  the  peripheral  end  of 
the  anterior  root  and  the  central  end  of  the  posterior  root  will  be  seen 
to  have  assumed  a  greyish  appearance,  which  contrasts  with  the  normal 
whitish  colour  of  the  two  ends.     Microscopic  examination  shows  the 


Fig.    18. — Experiments  of  Waller,  on  which  the  laws  of  degeneration  are  foiuided. 

Above  on  the  left,  section  of  the  posterior  root  between  the  ganglion  and  the  spinal  cord  ; 
below  on  the  right,  section  of  the  anterior  root  ;  below  on  the  left,  section  of  the  posterior  root 
between  the  ganglion  and  the  peripherj-  ;  above  on  the  right,  section  of  the  mixed  truiik  formed 
by  the  union  of  the  roots. 

In  each  ease  degeneration  attacks  the  segment  which  is  separated  from  the  nucleus  of  origin 
of  the  nerve  (spinal  ganglion  for  the  posterior  root,  spinal  cord  for  the  anterior  root). 


presence  in  this  end  of  the  nerve  of  extreme  disorganization.  At  the 
same  time  it  is  noticed  that  the  two  degenerated  segments  are  no  longer 
excitable.  Stimulation  of  the  peripheral  end  of  the  anterior  root, 
motor  in  function,  as  we  shall  see  further  on,  no  longer  causes  the 
muscles  to  contract  ;  and  the  central  end  of  the  posterior  root,  sensory 
in  function,  no  longer  excites  pain  when  it  is  pinched  or  faradized. 
Of  the  four  ends  or  segments  produced  by  the  section,  two  have  not 


32 


ELEMENTARY   NERVOUS   FUNCTIONS 


degenerated  :  these  are,  as  regards  the  anterior  root,  that  which  re- 
mains connected  with  the  grey  matter  of  the  spinal  cord  and,  in 
the  posterior  root,  that  which  is  still  connected  with  the  ganglion  of 
this  root.  Two  have  degenerated  :  namely,  those  which  have  been 
separated  respectively  from  one  and  the  other  of  these  two  organs. 
Waller  called  them  their  trophic  centres,  and  this  term  is  still  used. 

These  two  examples  appear  to  show  that  the  degeneration  occurs 
strictly  according  to  the  direction  in  which  the  nerve  conducts  the 
impulses,  towards  the  spinal  cord  as  regards  the 
sensory  nerves,  towards  the  muscle  in  the  case 
of  the  motor  nerves  ;  as  a  matter  of  fact  this 
is  not  so,  as  the  following  experiment  proves. 
If  the  posterior  root  be  cut,  no  longer  between 
the  ganglion  and  the  spinal  cord,  but  between 
the  ganglion  and  the  periphery,  it  is  the  cen- 
tral end  which  is  preserved,  and  the  peripheral 
end  which  degenerates.  To  sum  up,  the  end 
which  remains  intact  is  invariably  that  which  has 
preserved  its  connexions  ivith  the  cells  of  origin 
of  the  nerve  fibres  which  have  been  cut,  and  the 
other,  in  whatever  direction  conduction  may 
be  effected,  is  doomed  to  destruction. 

In  current  language,  these  facts  are  in- 
terpreted in  the  following  manner  :  the 
anterior  and  the  posterior  root  are  formed  by 
the  prolongations  of  the  neurons  whose  cells  of 
origin  are,  as  regards  the  first,  in  the  spinal 
cord,  and,  as  concerns  the  second,  in  the  root 
ganglion.  Every  prolongation  separated  from 
its  cell  is  destined  to  be  destroyed  ;  whether 
axon,  dendrite,  or  the  equivalent  of  any  one 
of  these  parts  its  lot  will  be  the  same.  The 
cell,  on  the  contrary,  which  was  originally  the 
germ  of  the  neuron,  and  which  possesses  the  power  of  preserving 
it,  as  it  formerly  had  the  power  of  creating  it,  is  maintained 
intact,  both  it  and  the  fibres  or  segments  of  fibres  which  remain  in 
connexion  with  it. 

Remark. — The  neurons  of  the  posterior  roots,  so  accessible  to  analy- 
sis in  consequence  of  the  arrangement  of  their  prolongations  in  two 
directly  opposed  directions,  do  none  the  less  form  a  particular  case, 
which  is  somewhat  rare  as  regards  all  the  arrangements  which  the 
neurons  affect.     Speaking  generally,  the  body  of  the  cell  is  found  at 


Fig.  19.— Section  of  the 
anterior  and  posterior 
roots  near  the  spinal 
cord.  Appearance  of 
the  fibres  after  several 
days. 

On  the  left,  posterior  root 
of  which  the  fibres,  having 
preserved  their  connexions 
with  the  cells  of  the  spinal 
ganglia,  have  remained 
healthy  ;  on  the  right,  an- 
terior root  whose  fibres,  sepa- 
rated from  their  cells  of 
origin,  have  degenerated 
(segmentation  of  myeUn). 
(Augustus  Waller.) 


THE  NERVOUS  ELEMENT  33 

the  origin  of  the  neuron,  in  such  a  way  that,  from  the  experimental 
point  of  view,  a  section  can  only  be  performed  on  the  axon  or  the  axis 
cyhnder  prolongation.  Under  these  circumstances,  which  are  those 
usually  present,  degeneration  ensues  in  the  direction  of  the  conduction. 
Hence  the  method  of  degeneration  may  be  employed  in  order  to  ascer- 
tain in  what  direction  impulses  are  conducted  in  certain  nerve  bundles 
(especially  as  regards  the  spinal  cord  and  brain). 

Laws  of  Waller. — 1.  Nerves  (Nerve  Fibres)  when  separated  from 
their  trophic  centres  (Nerve  Cells)  degenerate. 

2.  The    direction    of  the  degeneration  is  independent  of    that  of    nerve 

conduction 

Nutrition  and  Conduction. — The  attempt  has  often  been  made  to  connect  the 
direction  of  degeneration  with  that  of  the  conduction  of  impulses,  in  such  a  way 
as  to  include  the  two  phenomena  in  one  and  the  same  law  expressed  by  a  single 
formvda.  The  example  of  the  sensory  nerves  in  the  posterior  roots  proves  that 
there  is  no  necessary  connexion  between  them.  The  process  by  wliich  the 
neuron  preserves  its  existence  and  that  by  which  it  conducts  the  impulse  may 
indeed  be  related,  being  mutuallj-  dependent,  but  they  are  fundamentally  and 
essentially  distinct.  It  is  merely  necessary  to  be  reminded  that,  from  the  mor- 
phological standpoint,  the  case  of  the  posterior  roots  is  a  special  one.  The  cellu- 
lipetal  and  cellulifugal  prolongations  of  the  spinal  cell  have  therein  the  same 
organization,  that  of  axons  or  fibres  covered  with  myelin  ;  and  thus  we  see  that 
the  myelinated  fibres  are  dependent  on  the  cell  whatever  position  they  may 
occupy  with  I'egard  to  the  latter.  On  the  other  hand,  we  are  not  aware  of  what 
passes  in  the  protoplasmic  prolongations,  or  dendrites,  after  they  are  separated 
from  the  nerve  cell.  It  is  probable  that  they  degenerate  and  finally  disappear 
by  absorption  of  their  substance. 

Trophic  and  functional  centres. — From  the  distinction  thus  established  between 
the  process  of  conservation  (or  of  degeneration)  and  that  of  nervous  function, 
another  arises  wliich  is  adso  of  importance.  Usually  "  centres  "  imply  localities 
in  which  the  connexions  of  similar  or  different  parts  are  organized  and  united 
in  order  to  form  a  common  force.  The  experiments  of  Waller  prove  that  the 
connexions  which  the  different  jDortions  of  the  neuron  gather  together  are  centred 
in  the  nerve  cell,  whence  the  name  of  trophic  centre  is  given  to  this  latter.  In 
their  turn  the  nevu'ons  associate  and  collect  thenxselves  together  in  more  or  less 
independent  systems,  in  functional  centres  (or  nervous,  properly  so-called).  This 
association  of  nerve  elements  is  effected  by  their  prolongations  in  the  compli- 
cated connexions  contracted  by  the  latter  in  the  interior  of  the  grey  matter. 
Thus  the  functional  centres  are  distinct  from  the  trophic  centres,  with  which 
they  have  been  confounded. 

Generalization, — The  laws  of  Waller  are  general  laws.  They  may 
be  verified  in  all  nerves,  in  the  tracts  found  in  the  spinal  column  and  in 
the  brain  and  the  great  sympathetic  system. 

Laws  of  cells. — I  consider  that  these  laios  are  not  only  applicahle  to 
the  elements  composing  the  nervous  system,  hut  to  every  cell  element. 
Every  cell  contains  an  original,  germinative,  constructive  and  con- 

P  P 


34  ELEMENTARY  NERVOUS  FUNCTIONS 

servative  portion  as  regards  form  and  structure,  and  a  differentiated 
part  as  regards  its  functional  relations  with  other  elements.  The 
latter  is  dependent  on  the  former  and  cannot  exist  without  it  ;  yet 
the  converse  is  possible,  at  all  events  for  a  certain  time,  and  in  certain 
conditions. 

Loss  of  excitability. — After  section  of  the  nerve,  the  latter  does  not 
immediately  lose  its  characteristic  properties.  The  rupture  of  equili- 
brium which  results  from  isolation  from  its  nutritive  centre  does 
not  exert  its  full  effect  until  after  some  days.  During  this  period  the 
nerve  preserves  a  local  life,  thanks  to  its  vascular  connexions.  After 
twenty-four  hours  it  is  still  excitable  ;  it  may  be,  indeed,  that  its  ex- 
citability is  increased.  In  the  dog,  according  to  Longet,  this  excitability 
completely  disappears  after  four  days.  In  the  rabbit,  according  to  Ran- 
vier,  it  disappears  after  forty-eight  hours  ;  in  the  pigeon,  after  two  and 
a  half  to  three  days  (Waller).  In  the  frog  and  cold-blooded  animals 
it  continues  much  longer  than  in  mammals.  In  the  first,  especially, 
it  varies  very  greatly  according  to  the  season  ;  in  other  words,  accord- 
ing to  the  temperature.  In  the  frog,  in  the  winter,  the  excitability 
may  persist  up  to  thirty  days  after  section  (Brown-Sequard).  Further, 
this  persistence  of  excitability  varies  even  in  the  same  animal  according 
to  its  nutritive  condition  and  its  vitality. 

Structural  alterations. — The  neuron  is  a  symbiosis.  The  superadded 
cells  form  a  sort  of  sheath  for  its  axon  (sheath  of  Schwann),  which  is 
separated  from  the  axis-cylinder  by  an  internal  layer  of  myelin.  In 
the  cut  nerve,  the  unity  between  these  parts  is  broken  ;  the  myelin 
becomes  segmented  ;  the  protoplasm  of  the  cells  of  the  sheath  becomes 
thickened  ;  the  axis-cylinder  falls  in  pieces  and  is  re-absorbed  ;  the 
nuclei  increase  in  number  ;  and  the  sheath  persists  as  the  sole  relic  of 
the  nerve  thus  destroyed  and  deprived  of  its  functions  (Ranvier). 

In  the  spinal  cord  and  the  brain,  in  which  a  genuine  sheath  of  Schwann 
is  wanting,  these  changes  are  carried  out  in  a  slightly  different  manner, 
but  the  essential  result,  loss  of  excitability  and  disappearance  of  the 
axis  cylinder,  is  the  same.  The  neuroglia,  by  filling  up  the  cavity  left 
by  the  degenerated  fibres,  gives  a  peculiar  appearance  to  a  section  of 
the  latter  which  is  characteristic  of  degeneration  in  a  slightly  advanced 
stage. 

2.  Ascending  degeneration. — If  that  part  of  the  neuron  which  is 
separated  from  its  cell  of  origin  is  doomed  to  certain  destruction,  the 
other  portion  which  has  maintained  its  relation  with  this  cell 
also  experiences  the  counter  effects  of  this  amputation  (Nissl).  It 
may  be  that  it  degenerates  wholly,  including  the  cell  ;  it  may  be  that 
it  survives  and,  in  this  case,  regeneration  of  the  destroyed  portion 


THE  NERVOUS  ELEMENT  35 

may  more  or  less  completely  ensue  ;  but  even  when  this  happens 
changes  in  its  appearance  will  be  present,  indicating  internal  alterations 
of  its  structure. 

Conditions  which  are  necessary  for  survival. — We  have  seen  that 
degeneration  occurs  indifferently  in  the  upward  or  downward  pro- 
longation of  the  cells  (as  regards  the  conduction  of  impulses),  whenever 
these  prolongations  are  separated  from  them  ;  but  in  order  that  it 
may  survive,  it  is  not  a  matter  of  indifference  to  a  cellular  element, 
mutilated  or  not,  whether  it  receives  impulses,  or  is  completely  deprived 
of  them.  If  the  section  is  below,  it  receives  impulses  although 
incapable  of  transmitting  them  ;  if  the  section  is  above,  it  is  deprived 
of  them,  and,  in  the  second  case,  the  cell,  having  for  a  time  survived 
its  amputated  member,  finally  atrophies  and  disappears  (Van  Gehuch- 
ten).  Thus  it  is  easily  understood  that  section  of  a  posterior  root 
between  the  spinal  cord  and  the  ganglion  permits  the  continued  exist- 
ence of  the  cells  of  the  latter,  while  section  of  the  sensory  nerve  between 
the  ganglion  and  the  skin  necessarily  causes  their  destruction  (Lugaro). 
And  it  can  also  be  understood  that  section  of  a  motor  nerve  permits 
the  continued  existence  of  its  centre  of  origin.  This  persistence  is 
doubtless  due  to  the  reflex  or  voluntary  impulses  which  are  transmitted 
to  this  centre  by  the  connexions  which  it  has  preserved  (Marinesco, 
Goldscheider). 

Nature  of  the  change  ;  Chromatolysis.— Wliether  the  cell  is  to  survive  or  to 
die,  it  will  present  at  the  coiixnienceinent  the  same  modifications.  These  consist 
essentially  in  a  dissolution  of  the  chromatic  substance  in  the  enchyleme  {chromato- 
h/sis)  which  is  clearly  obvious  after  a  day  and  a  half  or  two  days,  but  more  mark- 
edly so  after  iour  or  five  days,  and  whicli  attains  its  maximum  towards  the 
fifteenth  day.  This  chromatolysis,  commencing  near  the  nucleus,  extends  to  the 
body  of  the  cell  in  order  to  attain  its  prolongations  ;  it  is  accompanied  with  a 
swelling  of  the  cell  and  with  a  displacement  of  the  nucleus.  If  the  process  stojjs 
here,  the  cell  will  survive  and  there  will  be  regeneration.  All  this  disorganization 
is  the  result  of  an  effort  for  the  reconstitution  of  the  type  of  the  mutilated  element. 
On  the  other  hand,  if  matters  go  further,  there  will  be  destruction  of  the  fibril- 
lary network  of  the  cell,  disorganization  of  its  protoplasm,  and  disappearance 
of  the  latter  (Van  Gehuchten). 

Its  phases. — The  alteration  v.-hich  ensues  in  the  cell  of  the  neuron  after  the 
separation  of  its  prolongations  is  only  then  a  true  degeneration  in  certain  cases  ; 
it  is  limited  in  other  circmnstances  (defined  above)  to  a  temporary  reaction, 
which  is  seen  to  be  inevitable,  after  such  an  important  nnitilation  of  the  neuron. 
Hence  the  change  will  present  phases  whose  result  differs  according  to  circum- 
stances. The  first  phase  will  be  that  of  reaction  ;  should  the  process  continue 
it  will  lead  sometimes  to  a  true  degeneration  or  destruction  of  the  nerve  cell  ; 
on  the  other  hand,  it  may  terminate  in  a  reparation  of  the  mischief  wliich  has 
been  ^\Tought  in  the  latter.  This  reparation  is  manifested  by  a  very  marked 
hypertrophy  of  the  cell,  and  by  its  deepened  colovu"  due  to  the  abundance  of  its 
chromatophile  elements  ;  sutiu^e  of  the  ends  of  the  cut  trimk  facilitates  this 
reparation  (Marinesco). 


36 


ELEMENTARY   NERVOUS    FUNCTIONS 


Application. — Tlie  reaction  of  Nissl  has  been  made  use  of,  especially  by  Marin- 
esco,  in  order  to  ascertain  the  nuclei  of  origin  of  nerves  after  total  section  of 


Fig.  20. — Chroniophile   substance   (granulations   in   black)   uf   se\'eral   types   of  nerve 
cells  (after  Van  Gehuchten). 
On  the  left,  bi-polar  cells  of  the  cornu  ammonis  in  the  rabbit  ;   on  the  right,   three  multipolar 
cells  of  the  nucleus  of    origin  of  the  oculo -motor    nerve.      In  the  degeneration  of    Nissl  the 
chromatic  substance  is  dissolved  from  the  nucleus  towards  the  prolongations. 

these  latter,  or  of  merely  a  part  of  their  bundles  of  distribution,  in  order  to 
discover  the  situation  of  these  nuclei,  or  rather  of  the  portions  of  them  which 
individually  corres])ond  to  these  bundles  of  fibres. 

Alteration  of  the  fibres.  —Not  merely  the  cells,  but  the  fibres  themselves  in  their 
journey  to  them,  present  modifications  consecutively  to  section,  modifications 
which  in  the  aggregate  are  very  different  from  those  of  Wallerien  degeneration, 
which  occurs  in  the  fragment  cut  off  from  the  axon.  They  are  slower  than  these 
latter  and  less  deep,  and  they  permit  the  persistence  of  the  axis  cylinder. 

This  degeneration,  known  as  retrograde,  which,  after  section  of  the  nerve,  ensues 
in  the  extremities  of  the  fibres  which  adjoin  the  cell,  should  be  clearly  distin- 
guished from  the  reaction  which  occurs  in  this  cell  contemporaneously  with  the 
Wallerien  degeneration.  The  reaction  of  Nissl  and  Wallerien  degeneration  are 
the  immediate  manifestations  of  the  mischief  which  ensues  in  the  neuron  in  con- 
sequence of  its  mutilation,  naanifestations  whose  progress  is  different  in  the  cell 
and  in  the  cut  axon.  Retrograde  degeneration  is  a  consecutive  manifestation, 
following  this  mutilation  and  the  disorder  which  ensues  upon  it. 

All  these  alterations  may  be  observed  in  the  peripheral  nerves  and  their  cells 
of  origin  (spinal  and  medullary),  in  the  elements  of  the  great  sympathetic,  in 
the  special  nerves  of  the  spinal  cord  and  of  the  brain.  Retrograde  degeneration 
is  most  frequently  met  with  in  these  latter  organs,  so  that  their  regeneration  is 
but  seldom  spoken  of,  contrary  to  what  is  noticed  in  the  peripheral  nerves. 

Equivocal  Sense  of  the  Word.— The  words  "  descending  and  ascending,"  used 
in  the  sense  just  pointed  out,  are  ill  ciiosen.  In  the  first  place  they  are  faulty, 
inasmuch  as  degeneration  does  not  -progress  by  successively  attacking  different  por- 
tions of  the  length  of  the  nerve,  hut  affects  all  portions  simidtaneously,  and  progresses 
equally  in  all  portions  at  once.  Secondly,  they  are  equivocal,  inasmuch  as  they 
have  no  connexion  with  the  real  position  in  space  of  the  degenerated  segments. 


THE  NERVOUS  ELEMENT 


37 


It  would  be  better  to  speak  of  proximal  degeneration  as  regards  the  segment 
which  remains  in  connexion  with  the  cell,  and  of  distal  degeneration  for  that 
which  is  separated  from  it. 

On  the  other  hand,  when  it  is  merely  a  question  of  Wallerien  degeneration,  by 
far  the  most  easily  recognized,  in  the  case  of  section  of  the  spinal  cord,  the  de- 
generation will  be  descending  for  the  fibres  whose  cells  are  situated  above  the 
section  and  ascending  for  those  whose  cells  are  below  it,  without,  however, 
ceasing  to  be  distal. 

Ascending  neuritis.  —  The  description  which  has  just  been  given  only 
includes  those  alterations  which  follow  the  interruption  of  continuity  of  nerve 
fibres  and  the  ruptiu-e  of  their  nutritive  equilibrium,  which  is  the  direct  conse- 
quence thereof  as  regards  t)ie  nem-on.  Under  different  toxic  or  pathological 
influences  the  nerve  may  present  various  alterations,  among  which  the  preceding 
may  occur,  but  which  do  not  concern  in  a  more  direct  manner  the  physiological 
study  of  the  nervous  tissue. 

3.  Atrophic  degeneration. — Like  every  cell  element,  the  neuron  is 
susceptible  of  undergoing,  through  prolonged  default  of  functional 
activity,  an  atrophy  or  diminution  of  all  its  component  parts  without 
any  notable  change  in  its  structure.  This  atrophy  is  the  consequence  of 
the  isolation  which  reaches  certain  neurons  after  a  time  when  those  which 
come  before,  themselves  destroyed  by  degenerative  changes,  no  longer 
furnish  the  impulse  which  is  normally  supplied  to 
the  former.  Considered  ^ith  regard  to  the  union 
Avhich  exists  between  the  elements  of  the  nervous 
system ,  section  of  a  bundle  of  nerves  may,  in  certain 
conditions,  bring  about  the  three  orders  of  degener- 
ation :  Wallerien  degeneration  in  the  fibres  separated 
from  their  cells  ;  ascending  degeneration  in  fibres 
united  to  cells  ;  atrophic  degeneration  in  elements 
which  are  deprived  of  impulses  by  the  degeneration 
of  the  preceding. 

Remark. — By  these  experiments  of  merotoniy,  we  tluis 
are  enabled  to  demonstrate  the  existence  in  the  neuron  of 
internal  functions  which  establish  a  dependence  between  its 
parts.  We  are  also  able,  in  a  certain  degree,  to  locaUze  the 
fiuictions,  by  proving  that  the  portions  of  the  neuron 
which  have  preserved  their  relations  with  the  nucleus  of  the 
nerve  cell  are  capable  of  survival,  the  nucleus  being  appar- 
ently an  organ  which  is  essential  for  nutrition  to  be  main- 
tained. But  we  know  nothing  of  the  reason  of  this,  the 
intimate  detail  of  these  relations  being  imdetermined.  And 
this  point  is  ec^ually  unknown  to  us  as  concerns  every  kind 
of  cell  as  well  as  the  nerve  cell. 


4.  Regeneration. — When  the  nerve  cell  escapes 
destruction  (which  is  the  rule  in  ordinary  conditions), 
it  undertakes  the  reconstitution  of  the  segment  of 
the   degenerated    fibre.      The    extremity,    or  the  distal    end,    swells, 


Fig.  21. —  Regen- 
eration of  nerve 
fibres,  several 
montlis  after  sec- 
tion (after  Ran- 
vier). 

From  the  cut  ex- 
tremity of  the  old 
nerve  fibre  one,  and 
often  several,  new 
smaller  fibres  bud 
out. 


38  ELEMENTARY  NERVOUS    FUNCTIONS 

sometimes  even  divides,  and  in  this  way  supplies  one  or  several 
growing  points,  from  which  axiscyhnders  take  their  rise,  these  latter 
re-establishing  more  or  less  completely  the  former  connexions.  When 
these  fibres  have  again  found  their  way,  either  within  or  between 
the  empty  sheath  of  Schwann,  regeneration  follows  its  regular  course. 
Vanlair  considers  that  the  rate  of  growth  is  about  a  millimetre  a  day. 
The  degenerated  fibres  whose  connexions  arc  re-estabhshed  again 
assume  their  functions,  and  thus  their  local  excitabiUty.  Conductivity 
re-appears  before  excitabihty  (Duchenne,  Erb,  Ziemsenn,  Weiss). 

Nerve  suture. — Hence  suture  of  the  two  ends  of  a  cut  nerve  favours 
the  speedy  regeneration  of  the  cut  and  degenerated  segment.  In 
certain  cases  the  reappearance  of  the  functions  of  the  injured  nerve 
has  been  so  rapid  that  it  has  been  thought  that  immediate  reunion  of 
the  cut  fibres  has  ensued  (Schiff,  Herzen).  It  is  clear  that  it  is  not 
possible  to  directly  negative  the  feasibility  of  such  a  reunion.  But, 
apart  from  the  fact  that  it  would  remain  an  exceptional  case,  it  is 
advisable  to  be  suspicious  of  supplementary  phenomena  of  all  sorts 
which  are  capable  of  restoring  more  or  less  completely  disturbed  or 
vanished  nerve  functions.  The  re-establishment  of  continuity  of  the 
nerve  should  be  affirmed  only  when  direct  proofs  thereof  are  available  : 
such  would  be  the  stimulation  of  a  previously  cut  nerve,  which  has 
been  then  isolated  for  a  certain  portion  Of  its  length  and  stimulated 
above  the  suture,  and  in  the  case  when  this  stimulation  should  produce 
its  ordinary  effects  before  the  delay  necessary  for  the  regeneration  of 
the  cut  fibres. 

Non-regeneration  of  nervous  cells  which  have  been  destroyed. — 
Duval  and  Laborde,  Brown-Se.quard,  Vitzou  have  concluded,  from 
their  experiments,  that  regeneration  of  the  nerve  centres  after  partial 
ablation  of  certain  portions  of  the  same  is  possible.  Juliana,  Magini, 
Schiefferdecker,  Cohen,  and  many  others,  have  protested  against  these 
results,  and  hold  with  Bizzozero  that  the  nervous  tissue  is  one  ivhose 
elements  are  persistent,  incapable  of  multiplication  and  of  renewal  after 
destruction.  A  tendency  to  regeneration  is  alone  observed  ;  cary- 
ocinesis  does  not  extend  to  a  division  of  the  protoplasm.  The  tissue 
which  supports  the  structure,  whose  power  of  multiplication  is  very 
considerable,  attacks  the  nerve  cell  and  fills  up  the  lacunae  left  by  its 
destruction  (Marinesco). 

Suture  between  centrifugal  nerves  of  different  functions. — Calugareanu  and 
V.  Henri,  after  having  divided  the  hypoglossal  and  lingual  nerves,  have  sutvu'ed 
the  central  end  of  the  first  with  the  peripheral  end  of  the  second.  After  the 
lapse  of  some  months  they  have  noticed  an  exaggerated  function  of  salivation  on 
the  part  of  the  sub-niaxillary  gland  of  the  corresponding  side  every  time  that  the 
animal  masticated,  as  if  the  motor  impulses  proceeding  from  the  nucleus  of  the 


THE  NERVOUS  ELEMENT  39 

hypoglossal,  instead  of  going  to  the  tongue,  proceeded  to  the  sub-maxillaiy 
gland.  Having  exposed  the  hj'poglossal  nerve  above  its  point  of  union  with 
the  lingvial,  they  have  ascertained  that  its  stinuUation  causes  secretion  in  the 
corresponding  gland  of  a  large  quantity  of  saliva  which  was  capable  of  trans- 
forming starch  into  sugar. 

The  lingual  nerve  contains  not  only  centripetal,  but  also  centrifugal  fibres, 
wliich  come  to  it  from  the  chorda  tj^mpani  nerve,  and  certain  of  wliich  go  to 
the  sub-maxillary  gland.  The  fact  discovered  by  these  authors  is  explained, 
not  by  assmning  that  the  fibres  of  tlie  hypoglossal  have  become  welded  with 
those  of  the  chorda  tympani,  but  that  these  fibres  (at  the  point  of  departvu'e  of 
its  central  end  which  has  been  imited  to  tlie  lingual)  have  swollen  out  and  occu- 
pied the  empty  sheaths  of  the  degenerate  chorda  tympani.  and  have  come  into 
contact,  through  their  new  terminations,  with  the  cells  of  the  sub-maxillarj' 
gland  wliich,  by  their  irritation,  are  excited  to  functional  activity.  The  motor 
impulses  of  the  hypoglossal  nerve  (when  the  animal  eats)  become,  through  this 
change  of  route,  secretory  impulses.  The  fact  is  interesting  because  it  proves 
that  a  nerve  usually  inotor  in  function  may  become  a  secretory  nerve.  The  stimulus 
which  the  first  conimunicates  to  the  muscle  should  be  of  the  same  natiu'e  as  that 
which  the  second  supplies  to  the  gland,  since  the  one  may  in  a  functional  sense 
take  the  place  of  the  other. 

In  other  words,  the  process  (whose  intimate  nature  is  unkno^\^l)  of  the  stimu- 
lation of  organs  by  their  nerves  would  appear  to  be  the  same  in  every  tissue. 

Langley  has  also  observed  that  the  central  end  of  the  vagus  nerve  may,  when 
it  is  united  to  the  peripheral  end  of  the  sympathetic,  give  rise  to  jDhenomena  of 
the  same  natxire.  Stimulation  of  the  vagus  above  the  reunion  of  the  two  nerves 
produces  the  ordinary  effect  of  that  of  the  sympathetic. 

2.  External  connecting  functions  or  nervous  functions,  properly  so  called. 
— The  neuron,  Avhen  once  its  personal  existence  is  assured,  assumes, 
like  every  cell  in  the  organism,  a  special  function  in  virtue  of  Avhich 
it  is  differentiated.  We  have  already  said  that  this  function  is  distin- 
guished from  others  inasmuch  as  it  is  not,  properly  speakitig,  a  function 
initiating  energy,  but  a  junction  ivhich  directs  energies  developed  by  other 
cells. 

The  methods  by  which  this  function  is  exercised  are  almost  unknown 
to  us,  but  the  aim  of  the  function  we  are  acquamted  with.  In  the 
nerve  something  is  transmitted  in  a  definite  direction  ;  the  nature  of 
this  something  we  are  ignorant  of  ;  on  the  contrar^^  its  objective  is 
clear  :  it  is  to  cause  the  organs  to  pass  from  a  state  of  repose  to  one  of 
activity  ;  in  present-day  language,  to  set  free  their  tensions,  to  expend 
their  potential  energies.  To  this  something  we  apply  the  name  excita- 
tion, an  expression  which  recalls  its  end,  but  says  nothing  as  to  its 
modality,  and  which,  for  this  reason,  has  no  equivalent  in  physics, 
where  the  end  of  phenomena  is  not  taken  into  consideration. 

The  nerve  receives  impidses  at  one  of  its  extremities  and  transmits  them 
at  the  other. 

Internal  and  external  acts,   properties  and  functions. — The  external 
manifestations  considered  apart,  by  which  the  cellular  elements  of  the 


40  ELEMENTARY  NERVOUS   FUNCTIONS 

organism  manifest  their  functions,  proceed  from  internal  actions  of 
these  elements,  which  are  sometimes  called  their  'properties.  For 
example  :  the  movement  which  is  amplified  by  the  osseous  levers,  and 
which  manifests  the  functional  motricity  of  the  muscles,  proceeds 
from  an  act  internal  to  the  muscle,  contraction,  or,  if  it  is  thought  pre- 
ferable, from  a  specific  property  of  the  muscular  elements,  contractility . 
Hence,  in  order  to  characterize  the  dynamic  aspect  of  the  muscle,  we 
can  refer  equally  to  its  property  or  to  its  function,  because  we  are  well 
acquainted  with  both,  and  the  relations  of  both  are  perfectly  clear. 

When  we  wish  to  specify  the  nerve  in  actii,  we  are  much  more  em- 
barrassed, and  the  expressions  "  animal  spirits,"  "  nervous  influx," 
"  neurility,"  etc.,  which  have  been  successively  applied  in  physiological 
language,  without  one  indicating  any  superiority  over  the  other,  suffi- 
ciently prove  this.  Contractility  is  the  expression  of  a  definite  change 
in  the  form  of  the  muscles,  a  change  towards  which  all  the  special  acts 
of  muscular  tissue  converge.  Neurility  merely  expresses  the  idea  of  a 
change  localized  in  the  nerve,  a  change  which  we  know  must  exist,  but 
which  it  is  impossible  for  us  to  define. 

As  we  are  incapable  of  defining  the  internal  nervous  act,  it  remains 
to  consider  the  function  of  this  act,  that  is  to  say,  its  utilization  apart 
from  the  nerve  element  itself ,  in  order  to  give  it  an  appropriate  name 
by  which  it  may  be  recognized  as  often  as  we  shall  have  occasion  to 
speak  of  it.  This  function  is  only  knoAvai  to  us  from  a  wholly  general 
point  of  view,  but,  in  this  sense,  this  knowledge  is  of  extreme 
importance.     It  is  the  function  which  we  call  stitnulation. 

From  a  functional  point  of  view,  the  currents  which  pass  through 
the  nervous  system  in  such  a  diversified  manner  are  currents  of  excita- 
tion. It  is  the  essential  function  of  the  nervous  system  to  be  htimu- 
lated,  and  to  transmit  this  stimulus  to  the  organs. 

This  function,  then,  is  that  of  each  of  its  component  elements  which 
are  excited  successively  or  contemporaneously,  and  which  finally  give 
rise  to  the  stimulation  of  organs  which  make  use  of  energy  under  all 
its  forms. 

1.  Numerical  connexion  of  the  exciting  energy  with  the  energy 
furnished  by  muscle. — The  notion  that  the  energy  given  out  by 
the  muscular  tissue  is  furnished  to  this  tissue  by  the  nervous  system 
is  so  widespread  that  it  will  be  useful  to  refute  it  by  an  experimental 
fact. 

Let  the  gastrocnemius  muscle  of  a  frog,  maintaining  its  connexion 
with  its  motor  nerve  (sciatic),  be  prepared  ;  and  let  an  artificial  stimulus 
of  electrical  nature  be  applied  to  this  nerve  ;  in  this  way  a  definite 
quantity  of  energy  will  be  expended  ;    as  the  result  of  this  stimulation 


THE  NERVOUS  ELEMENT  41 

the  gastrocnemius  muscle  executes  work  which  is  also  definitely  known. 
In  this  way  we  can  compare  the  quantity  of  energy  which  our  exciting 
apparatus  supplies  to  the  nerve  with  that  which  our  myographic 
apparatus  receives  from  the  muscle. 

Energy  supplied. — The  energy  supplied  to  the  nerve  by  a  condenser 
is  less  than  0001  Erg  (millieme  Erg). 

Recujterated  energy. — The  energy  expended  by  the  muscles  to  raise 
a  weight  of  200  grammes  0-5  of  a  centimetre  eciuals  100  grammes- 
centimetres,  which  makes  100,000  Ei'gs  (one  hundred  thousand  Ergs)- 
According  to  Weiss,  who  has  worked  out  the  elements  of  this  calcula- 
tion, the  ratio  of  work  produced  to  work  expended  is 

100.000  ^  ,00,000.000 
0001 

The  recuperated  energy  is  100,000,000  times  greater  than  the  energy 
supplied  to  the  small  system  which  is  experimented  on. 

When  it  is  remembered  that  the  mechanical  work  of  the  muscle 
represents  merely  a  fraction  of  its  total  energy,  a  considerable  portion 
of  which  is  carried  off  as  heat,  it  will  be  obvious  that  the  preceding 
figure  is  still  much  below  the  reality,  and  hence  that  the  ratio  sought 
for  must  be  still  greater. 

When,  further,  it  is  borne  in  mind  that  electric  stimulation,  however 
powerful  it  may  be,  produces  a  result  which  is  probably  inferior  to 
that  due  to  the  stimulation  of  the  nerve  by  a  muscle,  or  of  one  nerve 
by  another,  it  is  clear  that,  as  regards  the  total  energies  expended  by 
the  organism,  that  of  the  nerves  is  quite  negligible,  without  ceasing, 
however,  to  be  real. 

Artificial  stimuli,  compared  amongst  themselves,  yield  also  strik- 
ingly different  results.  According  to  Tigerstedt,  when  mechanical 
stimulation  is  made  use  of,  the  ratio  of  the  resulting  work  to  the  force 
of  the  excitation  is  about  320  ;  a  result  which  is  very  weak  when 
compared  with  that  of  electrical  stimulation. 

Conclusion. — The  idea  (for  a  long  time  indeed  questioned  by  physi- 
ologists, but  still  admitted  without  discussion  by  physicians)  must  be 
abandoned,  that  the  nervous  system  is  a  route  for  the  conduction  of 
power  in  the  organism  ;  as  a  matter  of  fact  it  is  a  pathway  followed 
by  an  infinitesimal  portion  of  the  external  energies,  which  is  utilized 
for  the  purpose  of  organizing  the  emplo^anent  of  force,  and  which  we 
call  exciting  energy,  to  distinguish  it  from  the  efficient  energies  which 
we  take  in  with  the  ingesta,  which,  circulating  in  the  vessels  with  the 
blood,  are  stored  up  as  reserves  in  the  tissues,  and  leave  the  body 
with  the  excreta. 


42  ELEMENTARY  NERVOUS   FUNCTIONS 

2.  Excitability  and  conductivity. — By  one  of  its  poles  the  neuron 
receives  stimuli  ;  by  the  other  it  transmits  them  to  that  which  follows- 
it.  There  is  clearly  a  transjDort  of  these  impulses  in  the  space  between, 
the  two  poles.  These  three  phenomena,  reception,  conduction  and 
transmissio7i  or  emission,  which  take  their  origin  and  play  their  part 
in  the  intimate  structure  of  the  nervous  element  from  its  dendrites 
to  its  intra-muscular  terminals  in  passing  through  the  axis  cylinder, 
obviously  suggest  to  us  that  they  are  dependent  on  the  movements  of 
the  nervous  substance.  These  movements  are  invisible  ;  they  cannot 
be  detected  even  with  the  highest  microscopic  powers  ;  doubtless 
the}^  are  molecular,  but  this  should  not  be  considered  as  an  invincible 
obstacle  to  our  acquiring  a  knowledge  of  them.  In  the  present  state 
of  science  our  information  concerning  them  is  too  insufficient  for  us 
to  form  even  an  imperfect  idea  on  the  subject. 

Initial  shock. — The  initial  receptive  phenomena  which  communicate 
the  shock  to  the  dendrites  of  the  neuron  are  unknown  to  us  ;  the  pro- 
gression of  this  shock  in  the  axon  is  also  unknown,  as  is  the  manner 
by  which  it  leaves  the  terminations  of  the  axon  in  order  to  reach  the 
element  (nervous,  muscular,  glandular  or  other)  which  follows  it.  We 
have,  however,  reason  to  believe  that  all  these  phenomena  closely 
resemble  each  other,  whether  taking  place  in  the  different  neurons 
compared  amongst  themselves,  or  whether  in  the  extremities  and  the 
continuity  of  the  same  neuron.  The  infinite  variety  of  nervous  actions 
depends  less  on  the  individual  variety  of  the  elements  composing  the 
nervous  system  than  on  that  of  the  connexions  and  the  relationships 
which  exist  amongst  these  elements  themselves. 

In  this  connexion,  that  which  passes  at  the  origin  and  at  the  termina- 
tion of  the  nervous  system,  taken  in  its  entirety,  should  not  mislead 
us.  It  is  not  luminous  waves  which  pass  through  the  optic  nerve,  nor 
sonorous  waves  through  the  acoustic  nerve,  nor  a  mechanical  pressure 
through  the  nerves  of  touch.  All  of  these  have  been  originally  trans- 
formed by  special  apparatus  (the  organs  of  sense)  which  have  gathered 
them  together  under  that  modality  which  we  regard  as  uniform,  and 
which,  for  the  sake  of  convenience,  we  call  the  nerve  wave. 

The  same  reasoning  applies  to  what  passes  at  the  other  end  of  the 
nervous  system  ;  the  cells,  fulfilling  such  varied  functions,  which 
receive  this  wave  must  individually  possess  some  sort  of  apparatus 
which  adapts  the  uniform  impulse,  coming  from  the  different  nerves, 
to  the  special  structure  and  function  of  each  of  them.  The  molecular 
and  unstable  equilibrium  which  the  nerves  possess  the  power  of  destroy- 
ing in  it  probably  requires  to  be  attacked  in  a  slightly  different  manner 
according  to  the  special  conditions  of  each  case. 


THE  NERVOUS  ELEMENT 


43 


Specific  and  general  excitants. — A  specific  excitant  h  that  which  only 
acts  on  a  certain  class  of  element  which  is  well  defined  :  for  example, 
light  in  the  case  of  the  retina,  sound  in  that  of  the  internal  ear. 

General  excitants  are  those  which  act  indifferently  on  every  living 
element  and  every  organized  substance. 

Every  destructive  action,  such  as  a  prick,  traumatism,  burn,  chemi- 
cal change,  etc.,  sets  up  reaction  in  the  substance  which  it  tends  to 
destroy  ;  there  is  a  general  cause  of  excitation  with  which  it  is  useful 
to  be  acquainted,  but  which  is  of  small  value  as  a  method  of  study. 

Electricity  in  the  form  of  currents,  abruptly  penetrating  the  tissues 
(or  even  by  its  distant  effects,  when  the  electric  perturbation  is  very 
strong)  is,  on  the  contrary,  a  very  good  excitant.  This  excitant  is 
general,  that  is  to  say,  adapted  to  arouse  all  the  cell  activities.  Further, 
its  destructive  action  may  be  rendered  practically  nil  when  the  condi- 
tions of  its  employment  are  properly  chosen. 


^"-'^-^K 


Fig.  22. — Comparative  stimulation  of  a  muscle  and  its  nerve,  the  resulting  contraction 
being  recorded  on  a  rotating  cylinder. 
Z,  electric  element  ;  K,  rheotome  or  interrupter  ;  I,  primary  coil  ;  II,  secondary  coil  ; 
MX,  commutator  carrying  the  stimulation  at  will  to  the  muscle  by  wires  connected  witli  its 
two  extremities,  and  to  the  nerve  by  wires  connected  with  a  i^ortion  of  its  length  (borrowed 
from   Waller). 

Electric  stimulation  has  been  the  means  of  causing  great  progress 
in  nervous  physiology,  because  this  procedure  has  rendered  the  analysis 
of  the  different  systematic  and  cellular  functions  much  easier  ;  the 
little  that  is  known  concerning  the  analysis  of  the  nerve  itself  is  chiefly 
due  to  it. 

Evidences  and  estimation  of  nerve  activity. — We  say  that  the  nerve 
is  excitable  ;  we  notice  on  the  other  hand  that  no  alteration  is  visible 
in  it,  no  apparent  movement ;  what  proof  then  have  we  of  its  activity 
if  the  latter  consists  of  purely  molecular  movements  ?  In  order  to 
demonstrate  and  study  this  question,  there  are  two  methods  available, 
both  indirect. 

(1)  We  notice  the  repercussion  of  its  activity  on  that  of  elements 


44  ELEMENTARY   NERVOUS   FUNCTIONS 

capable  of  changes  of  form  (the  muscles  especially)  to  which  it  com- 
municates its  excited  condition.  The  molecular  movement  of  the 
nerve  arouses  a  movement,  also  molecular,  in  the  muscle,  which  move- 
ment is  transformed  in  the  latter  into  a  mechanical  one,  into  work, 
so  much  the  easier  to  calculate  as  it  is  considerably  greater  than  that 
of  the  nerve,  although  being  (as  is  supposed,  at  least)  proportional  to 
it.  The  7nechanical  ivork  of  the  muscle  demonstrates  and  measures  the 
molecular  work  of  the  nerve.  ^ 

(2)  We  render  visible  and  measure,  with  the  galvanometer  or  the 
electrometer,  the  electric  motor  force  which  its  stated  activity  pro- 
duces in  the  nerve,  and  which  is  commonly  known  as  its  iiegative  varia- 
tion or  its  electric  current  of  activity. 

These  two  methods  have  each  their  advantages  and  their  drawbacks. 
So  long  as  purely  motor  nerves  are  the  subject  of  investigation,  the 
first  is  without  doubt  the  most  convenient  and  accurate  ;  but  when 
the  point  of  departure  of  the  stimulus  is  separated  from  the  muscles 
by  a  certain  number  of  relays  of  grey  matter,  the  transformations 
which  these  latter  produce  as  regards  the  impulse  which  passes  through 
them  clearly  hinder  the  muscles  from  indicating  in  an  accurate  manner, 
as  regards  extent  and  succession,  the  conditions  of  activity  of  the 
stimulated  nerve.  It  is,  then,  these  transformations  themselves  that 
the  muscles  reproduce  by  their  contractions.  It  is  thus  only  the  nerves 
in  direct  connexion  with  the  muscles  which  will  be  of  use  in  studying 
the  conditions  of  nervous  activity,  and  the  way  in  which  it  conducts 
itself  with  regard  to  external  shocks.  But  we,  in  principle,  admit 
that  all  neurons,  in  nearly  the  same  degree,  respond  in  the  same  manner 
to  stimulation.  In  applying  this  principle,  the  general  laws  concerning 
the  stimulation  of  nerves  have  been  deduced  more  especially  from 
investigations  made  on  those  nerves  which  are  directly  motor  in 
function. 

The  second  method  is  applicable  to  every  nerve,  to  every  nerve 
segment,  even  when  isolated  and  detached  from  the  animal  while  it 
is  still  living.  It  requires,  indeed,  that  the  nerve  be  divided  at  one 
extremity,  in  order  to  receive  the  derivation  of  the  electric  current 
which  is  to  be  estimated. 

It  is  delicate  in  application,  and  it  is,  for  want  of  a  better,  in  many 
cases  by  no  means  a  despicable  method  of  analysis. 

3.  Isolated  Conduction. — It  is  allowed,  and  can  be  demonstrated,  that 
the  different  fibres  of  the  sayne  nervous  trunk  do  not  communicate  from 

^  Tlie  word  worlc  is  here  used  in  the  sense  of  "  expenditure  of  energy,"  according 
to  the  definition  of  M.  Chauveau,  which  is  accepted  by  many  physiologists. 


THE  NERVOUS  ELEMENT  45 

one  to  the  other  any  of  the  impulses  which  separately  pass  through  them. 
The  only  points  by  which  the  neurons  transmit  the  impulse  are  situated 
at  their  initial  or  terminal  extremities  in  the  grey  matter  of  the  brain, 
of  the  spinal  cord,  or  of  the  ganglia.  The  necessity  of  such  an  isolated 
conduction,  in  order  that  the  functions  may  be  properly  carried  out, 
is  easily  understood.  If  this  were  not  so,  nervous  functions  would  be 
impossible. 

A  difficulty  arises  in  reconciling  this  law  with  that  which  has  just 
been  referred  to,  of  the  excitability  of  the  fibres  on  their  course,  and 
of  the  facility  with  which  the  impulses  may  penetrate  them.  This 
difficulty  is  overcome  when  it  is  noticed  that  this  faciUty  is  altogether 
relative.  It  is  sufficiently  marked  for  us  to  be  able,  hy  pressure  or 
electric  currents,  to  arrive  at  the  nerve  trunks  through  the  skin,  and 
to  arouse  them  to  activity.  But  it  is  great  enough  not  to  permit 
mechanical  or  electrical  actions,  which  are  far  Aveaker,  and  which  result 
from  the  change  of  form  in  the  muscles,  or  of  their  special  current,  to 
act  efficiently  on  them.  Further,  it  must  be  borne  in  mind,  that  these 
stimuli  are  artificial,  and  that  we  have  no  right  to  compare  them  (as 
regards  efficiency)  with  the  specific  excitations  of  unknown  nature  (but 
probably  neither  mechanical  nor  electrical)  which  normally  penetrate 
the  nerve  and  are  propagated  through  it. 

Nervous  induction. — When  two  bodies  or  two  systems  of  similar  bodies  are  in 
presence  of  each  other  and  when  the  plaj^  of  forces  in  the  one  arouses  in  the  other 
actions  similar  or  analogous  to  those  which  exist  in  the  first,  it  is  said  that  induc- 
tion occurs.  A  very  clear  example  of  this  is  furnished  to  us  by  the  studj"  of 
electricity,  by  the  so-called  electric  induction  and  that  known  as  viagnetic.  The 
word  has  in  these  two  cases  a  precise  significance,  because  the  conditions  of 
induction  are  rigorously  defined  in  it.  In  the  study  of  Ught,  phosphorescence 
and  fluorescence  are  sometimes  assimilated  to  phenomena  of  the  same  order, 
although  the  conditions  which  give  rise  to  them  are  far  less  accurately  kno^vTi. 
When,  by  stimulation  of  a  sensory  nerve,  we  arouse  the  activity  of  one  or 
several  nerves  (motor  or  other)  which  follow  it,  we  may,  for  our  part,  see  in  this 
re-echo  one  after  another  of  the  same  phenomenon  through  separate  elements, 
an  example  of  induction,  but  it  must  be  distinctly  tmderstood  that  the  word 
"  induction  "  has  here  (as  all  those  expressions  taken  from  jihysics — conduction, 
reflection,  polarization,  interference,  etc.)  merely  a  comparative  value,  and  in 
no  sense  an  explanatory  one.  There  may  therefore  be  a  nervous  induction,  as 
there  is  a  nervous  conduction,  without  the  electrical  nature  of  the  phenomenon 
in  the  two  cases  being  in  any  way  implied.  Or,  to  speak  more  acciirately,  we 
may  prove  that  in  the  nerve  a  certain  electric  conductivity  and  certain  electric 
or  magnetic  phenomena  of  induction  exist,  without  prejudging  the  real  nature 
of  the  mechanism  of  the  stimulation  of  one  nerve  by  another.  We  are,  so  to  say, 
assured  in  advance  that  the  conditions  of  the  physiological  phenomenon  are  not 
reducible  to  one  of  those  elementary  phenomena  of  energj'  which  physics  demon- 
strates in  a  state  of  isolation  in  its  schematic  experiments. 

So  far  as  concerns  magnetic  induction,  it  must  be  here  once  again  remarked 
that  special  precautions  have  been  taken  in  order  that  it  may  not  be  produced 


46  ELEMENTARY   NERVOUS   FUNCTIONS 

by  the  action  of  one  nerve  fibre  on  another  throughout  the  length  of  the  axons 
of  varying  function,  which  are  placed  joarallel  to  one  another  in  the  same  nerve 
trunk.  The  activity  of  one  nerve  fibre  never  involves  that  of  its  neighbour.  It 
only  involves  it  so  far  as  it  is  placed  in  relation  with  it,  in  the  interior  of  the 
nuclei  of  the  grey  matter,  or  of  the  ganglia.  It  is  this  fact,  clearly  demonstrated, 
which  is  expressed  by  the  law  of  isolated  conduction.  Throughout  the  course 
of  the  fibres,  not  only  is  conduction  (electrical  or  not)  isolated,  but  induction 
(electrical  or  not)  does  not  exist.  And  it  was  necessary  that  this  should  be  so 
in  order  that  the  nervous  system  might  discharge  its  functions  of  direction,  of 
rearrangement  of  the  impulse  which  are  both  variable  and  complicated,  throvigh 
the  tissues  of  the  organism. 

The  nerve  fibre,  the  axon,  is  a  closed  systena  analogous  to  that  of  our  tele- 
phones. If  a  point  exists  by  which  this  system  may  lose  its  definite  lines  of  force, 
so  that  these  may  act  on  lines  of  force  of  similar  systems,  it  can  only  be  at  its 
extremities,  at  its  receptive  and  emissive  poles.  The  structiu'e,  still  imperfectly 
known,  of  these  delicate  parts  shows  us  nothing  which  can  support  the  idea  of 
the  occurrence  of  a  phenomenon  of  this  kind.  The  experiments  which  would 
be  adapted  to  demonstrate  this  phenomenon  are  absolutely  impossible  of  per- 
formance. The  properties  of  the  bodies  and  of  their  surroundings,  the  nature, 
the  origin  and  transformation  of  energy,  are  in  the  special  case  wholly  unknown 
to  us.  The  nerves  transmit  an  impulse  with  the  greatest  facility  in  directions 
with  which  we  are  acquainted  ;  we  are  wholly  ignorant  of  the  manner  in  which 
they  transmit  it. 

4.  Propagation  in  the  two  directions. — In  the  normal  performance 
of  its  functions,  the  neuron  receives  the  impulse  exclusively  by  one  of 
its  poles,  which  is  invariably  the  same  ;  hence  it  follows  that  it  trans- 
mits the  impulse  invariably  in  the  same  direction,  that  is  to  say,  for 
example,  from  the  spinal  cord  to  the  muscles  in  the  case  of  the  motor 
nerves  ;  from  the  skin  to  the  spinal  cord  in  that  of  the  sensory  nerves. 
When  we  stimulate  the  nerve  artificially  in  its  normal  position,  we 
have  just  seen  that,  starting  from  the  stimulated  point,  the  impulse 
proceeds  towards  its  habitual  destination.  But  is  it  possible  that  at 
the  same  time  from  thence  it  may  be  transmitted  in  the  opposite  direc- 
tion, that  is  to  say,  contrary  to  its  normal  course  ?  The  question  has 
no  great  practical  interest,  since  it  involves  abnormal  conditions  ;  but 
it  has  an  importance  as  concerns  the  general  properties  of  nerve 
substance. 

In  order  to  settle  the  question,  it  would  be  necessary  to  turn  the 
neuron  round  by  inverting  its  two  poles,  the  receptive  end  becoming 
the  distributive  end,  the  distributive  the  receptive,  and  then  to  see  if 
the  impulses  (normal  or  artificial)  are  still  transmitted  in  this  new 
position.  This  total  inversion  being  impossible,  it  would  be  necessary, 
after  having  removed  a  segment  of  the  nerve  trunk  between  two  sec- 
tions, that  we  bring  this  inversion  about,  by  welding  together  the  two 
ends  and  then  observing  what  happens  in  this  new  position. 

This  experiment  has  been  attempted  by  several  authors,  especially 


THE  NERVOUS  ELEMENT  47 

by  P.  Bert,  who  employed  different  methods,  chiefly  on  rats'  tails, 
and  in  his  hands  it  appears  to  have  settled  the  question.  Yet,  on 
considering  it  more  closely,  it  seems  that  the  objection  may  be  urged 
that  the  segment,  in  this  way  cut  and  reversed  (even  when  the  opera- 
tion has  been  performed  at  several  sittings),  degenerates  and  is  replaced 
functionally  by  new  fibres  having  the  same  orientation  as  the  old 
ones,  which  obviously  deprives  the  experiment  of  demonstrative  value. 
The  laws  of  degeneration  being  known,  it  would  seem  that  the  attempt 
to  give  to  nerves  connexions  other  than  those  which  they  acquire  by 
their  development  must  be  given  up.  Yet  a  means  exists  by  which 
we  are  able  to  observe  the  state  of  activity  of  a  nerve  in  the  extremity 
in  which  we  believe  that  the  impulse  may  be  propagated.  This  method 
is  that  of  the  negative  variation  of  the  electric  currents  of  nerves. 

If  it  were  possible  to  deal  with  a  nerve  trunk  either  exclusively 
sensory  or  exclusively  motor  (not  containing  these  fibres  mixed 
together  in  any  proportion),  this  method  would  settle  the  question. 
Unfortunately  such  nerves  do  not  exist,  at  all  events  in  the  absolute 
manner  required,  so  that  the  question  must  still  remain  undecided. 
Without  doubt,  the  nervous  system  contains  an  arrangement  by  which 
the  passage  of  impulses  in  a  definite  direction  is  assured,  just  as  does 
the  circulatory  system.  Observation  proves  this,  the  evidence  being 
the  same  in  the  two  svstems.  In  the  second  case  the  controlling: 
apparatus  is  known  to  us  :  it  is  the  arrangement  of  valves  by  which 
the  cavities  of  the  heart  are  separated  the  one  from  the  other.  In  the 
first  case  neither  analysis  nor  our  intelligence  has  been  able  to  unravel 
the  problem.  But  it  may  be  that  there  is  some  remote  analogy  with 
the  arrangement  which  holds  in  the  vascular  system  ;  it  would  be, 
according  to  this  h^^pothesis,  localized  in  the  points  of  union  of  the 
neurons.  Between  these  points  the  impulse  would  be  able  to  travel 
in  either  direction,  but  these  points  once  passed,  it  would  be  impossible 
for  it  to  retrogress. 

5.  Integrity  of  structure. — If  a  nerve  is  cut  in  its  course,  it  ceases  to 
transmit  the  impulses  beyond  the  point  of  section.  Indeed,  if  its  two 
ends  are  adjusted  as  exactly  as  possible,  conduction  is  not  effected. 
It  depends  on  a  special  structure  which  has  been  destroyed  in  the  axon 
at  a  certain  point  of  its  course.  Nerve  conduction  is  indeed  a  mole- 
cular process  ;  it  is  rendered  impossible  by  a  local  derangement,  even 
a  very  limited  one,  or  an  alteration  in  the  arrangement  in  the  molecules 
of  the  nerve  structure. 

Welding  of  nerves.— Schiff  and  Herzen  have  maintained,  and  surgeons 
also,  that  the  two  ends  of  a  freshly  cut  nerve,  pared  and  sutured,  can 
unite  by  first  intention,  degeneration  being  hindered,  and  in  this  way 


48  ELEMENTARY   NERVOUS   FUNCTIONS 

the  loss  of  function  may  be  prevented.  On  the  other  hand,  Ranvier, 
Vanlair,  and  with  them  the  majority  of  physiologists,  consider  that 
degeneration  is  an  inevitable  consequence  of  section. 

6.  Local  excitability  of  the  different  portions  of  the  neuron. — In  the 
normal  condition  the  nerve  transmits  impulses  from  one  of  its  poles  to 
the  other.  Artificially,  it  can  receive  others  in  its  course,  which  com- 
port themselves  like  the  preceding. 

If  it  is  cut  across  its  length,  the  segment  attached  to  its  emissive  or 
distributing  pole  ceases  to  receive  the  current  from  the  receptive  pole, 
and  consequently  to  distribute  it  to  the  elements,  nervous  or  other- 
wise, in  which  it  terminates.  This  isolated  segment  nevertheless 
preserves  its  excitability  until  it  degenerates,  that  is  to  say,  during  two, 
three,  four  days  or  longer,  according  to  the  animal. 

This  tem]3orary  conservation  of  excitability  in  the  axon  separated  from  its 
cell  has  an  important  signification.  The  axon  (like  all  the  other  prolongations) 
depends  on  the  cell  for  its  nutrition,  for  the  conservation  of  its  internal  organiza- 
tion. It  does  not  depend  upon  it  immediately  for  that  which  we  know  as  its 
function.  Isolated  from  it,  it  yet  comports  itself  as  an  entire  neuron.  It  is 
capable  of  receiving  im])ulses  and  of  transmitting  them  to  its  extremity.  This 
is  precisely  the  role  of  the  nervous  system  in  the  organism,  namely  :  to  transmit 
an  impulse  from  one  point  to  another.  The  body  of  the  cell  of  the  neuron  is  an 
organ  necessary  for  the  organization  and  conservation  of  the  latter,  but  it  takes  no 
necessary  and  direct  part  in  its  power  of  functional  activity  properly  so  called. 

This  is  a  consequence  of  tlie  general  excitability  of  living  matter,  but  the  re- 
actional  manifestation  is  here  renaarkably  clear.  Along  the  whole  length  of  the 
axon  impulses  may  be  made  to  penetrate  the  latter  :  contact,  light  pressure, 
extremely  weak  electric  cvirrents  equally  sviffice  to  render  its  ordinary  action 
manifest.  Hence  between  the  receptive  jDole  and  the  rest  of  the  neuron  there 
is  no  essential  difference  of  properties. 

Excitability  and  conductivity. — Excitability  is  the  property  which  the  nerve 
possesses  of  reacting  to  the  stimulus  which  it  receives,  not  only  from  its  recep- 
tive pole,  but  throughout  its  course.  Conductivity  is  the  property  of  transmit- 
ting throughout  its  length  away  to  its  terminal  extremity  the  condition  of  excita- 
tion which  it  has  received.  An  attempt  has  been  made  to  ascertain  experi- 
mentally if  there  is  not  here  fundamentally  one  and  the  same  property,  the  con- 
duction resulting  from  parts  of  the  nerve  being  successively  excited  the  one  by 
the  other  ;  as  if  the  energy  liberated  at  each  point  acted  on  the  following  point 
by  causing  the  latter  to  give  off  its  intrinsic  energy,  and  so  on.  These  experi- 
ments aimed  at  subjecting  the  nerve  to  different  influences,  in  order  to  see  if  the 
two  phenomena  present  parallel  or  divergent  or  even  contrary  variations. 

It  may  be  said  that,  as  a  general  rule,  the  influences  which  modify  local  excit- 
ability modify  little  or  not  at  all  the  transmission  of  the  impulse  through  the 
part  of  the  nerve  thus  infivienced.  Example  :  a  small  portion  of  a  nerve  being 
submitted  to  the  action  of  CO 2,  comparative  stimulations  are  applied  to  the 
part  affected  and  above  the  latter  (with  regard  to  the  direction  of  the  trans- 
mission) ;  the  local  excitability  is  much  diminished,  while  the  stimuli  applied 
above  are  as  powerful  as  ever  (Grunhagen).  It  is  the  same  as  regards  variations 
of  temperature,  local  or  general  (G.  Weiss).  When  a  nerve  degenerates  (after 
crushing)  the  voluntary  impulses  again  become  efficient,  while  the  nerve  is  still 
locally  incapable  of  stimulation  by  electricity  (Erb). 


THE  NERVOUS  ELEMENT  49 

In  the  reasoning  which  is  at  tlie  foundation  of  these  comparisons  it  is  assmned 
that,  as  regards  the  hypothesis  of  conductivity  and  excitabihty  being  one  and  the 
same  thing,  the  artificial  excitant  (electricity)  and  the  natm-al  excitant  (physio- 
logical stimulation  of  one  segment  by  another)  possess  the  same  efficacy. 
Yet,  on  tlie  other  hand,  there  are  reasons  for  believing  that  the  artificial  excitant 
is  less  active,  and  that,  if  the  excitability  diminishes,  the  final  advantage  must 
remain  with  the  natural  excitant.  The  strongest  argument  in  favour  of  the 
dissociation  of  the  two  properties  lies  in  the  fact  that  the  temperature  does  not 
modify  the  conduction,  and  that  the  latter  remains  equal  to  itself  in  the  whole 
course  of  the  nerve  ;  it  is  only  in  these  two  points  that  there  is  still  a  variance 
between  experimenters. 

7.  Rate  of  conduction. — The  impulses  which  reach  a  nerve,  at  its 
origin,  or  in  one  of  its  points,  traverse  this  nerve  at  a  definite  rate, 
which  it  has  been  possible  to  reckon.  Helmholtz,  who  was  the  first  to 
measure  this  rate  in  the  nerves  of  the  frog,  has  found  it  to  be  about 
27  metres  a  second.  Chauveau,  who  has  studied  it  on  warm-blooded 
animals,  has  found  it  to  vary  according  to  the  nerves  operated  on,  and 
according  also  to  certain  circumstances  pecuUar  to  the  subject  or  to 
the  nerve  itself.  In  the  horse  it  is  about  70  metres  in  the  motor  nerves 
of  the  larynx,  and  only  about  8  metres  in  the  motor  nerves  of  the 
oesophagus. 

Method. — The  rate  (when  it  is  uniform)  is  the  distance  traversed  in  a  unit  of 
time  : 

t 
In  the  appHcation  of  this  formula,  e  represents  the  length  of  the  nerve  from  the 
point  stimulated  to  the  muscle  ;  it  is  calculated  without  difficulty  in  fractions 
of  a  metre,  by  direct  measm-ement.  t  is  the  time  which  elapses  between  the 
stimulation  of  the  nerve  at  a  given  point  and  the  contraction  of  the  muscle  ; 
its  determination  is  more  difficult  and  requires  special  arrangements.  The 
method  most  generally  employed  consists  in  inscribing,  on  a  surface  moving 
uniformly  (a  rotating  cylinder)  and  at  a  given  rate,  the  stimulation  and  the 
muscular  movement  on  two  parallel  lines  by  the  aid  of  styles  which  are  exactly 
superposed,  the  one  moved  by  tlie  exciting  electric  current  (electric  signal),  the 
other  by  the  miTscle  which  contracts.  The  time  which  elapses  between  the  two 
records  is  measured  by  the  distance  which  separates  them  in  the  direction  of 
the  movement  of  the  surface.  This  calculation  is  rendered  very  easy  if,  on  a 
third  line  parallel  to  the  two  others,  the  movements  of  a  tuning  fork  giving  100 
or  200  oscillations  a  second  are  recorded. 

Length  of  propagation  and  latent  period. — The  calculation  thus  made  may  still 
be  incorrect,  because  experiment  has  shown  that,  in  its  passage  from  nerve  to 
muscle,  and  independently  of  its  transmission  through  the  nerve,  the  impulse 
imdergoes  a  retardation  (or  latent  period),  which  it  is  necessary  to  deduct  from 
the  length  of  time  inscribed  on  the  registering  cylinder.  In  order  to  overcome 
this  difficulty  two  successive  determinations  of  excitation  are  made  on  the  nerve, 
by  choosing  two  points  of  the  latter  sufficiently  wide  apart.  If  t  be  the  diiration 
of  the  transmission  of  the  impulse  from  the  farthest  part  of  the  muscle,  and  n 
the  dm-ation  for  the  nearest  ])oint  ;  t  —  f^  is  the  time  occupied  by  the  impulse 
in  traversing  the  distance  from  the  first  of  the  points  to  the  second  ;  as  to  the 
space  traversed,  it  is  the  distance  which  separates  the  two  points,  and  which  is 
measured  directly  on  the  prepared  and  exposed  nerve. 

P.  E 


50 


ELEMENTARY  NERVOUS  FUNCTIONS 


In  the  first  experiments  of  Helmholtz  the  values  of  t  and  of  f^  were  determined 
by  making  use  of  the  method  of  Pouillet. 

Let  a  galvanometer  be  intercalated  in  a  conducting  circuit.  If  in  this  circuit 
a  current  of  a  given  duration  (fairly  short)  be  made  to  pass,  the  deviation  of  the 
needle  is  pro2)ortional  to  the  duration  of  the  passage  of  the  current.  The  exj^eri- 
ment  is  arranged  in  svich  a  way  that  the  current  which  should  pass  through  the 

galvanometer  is  made  (that  is  to  say,  com- 
mences) at  the  exact  moment  of  the 
stimulation  of  the  nerve,  and  is  broken 
(that  is  to  say,  ceases  to  joass)  at  the  exact 
moment  of  contraction  of  the  muscle.  In 
other  words,  matters  are  so  arranged  that 
the  stimulation  makes  this  current,  and  the 
contraction  which  ensues  breaks  the  con- 
tact which  permits  it  to  pass.  Two  ob- 
servations are  made,  by  exciting  the  nerve 
at  two  points  unequally  distant  from  the 
muscle.  In  this  way  the  two  unequal 
values  t  and  t^  are  obtained,  whose  differ- 
ence represents  the  time  sought,  T. 

Chauveau,  experimenting  on  the  nerves 


Fig.   23- — Estimation    of    the    rate    of 
conduction   in  a  nerve. 

Two  contractions  obtained  by  stimulat- 
ing two  points  of  the  nerve  separated  by 
a  definite  interval.  The  stimulation  is 
made  automatically  by  the  rotating  cylin- 
der at  tlie  same  phase  of  its  rotation.  The 
delay  of  one  of  the  contractions  measures 
the  time  required  by  the  impulse  to  pass 
over  the  space  between  the  two  points  of 


the  nerve  successively.     The  duration  of     of    the    larynx    of    large    mammals,     which 


this  delay  is  determined  by  a  length  which 
may  be  estimated  by  comparing  it  with 
other  lengths  representing  hundredths  of  a 
second  (waved  line  traced  by  the  vibrations 
of  a  tuning  fork). 


have,  as   is   well   known,    great   length  (on 
account     of    their    recurrent    course),    has 
combined  graphic  inscription  of    the  mus- 
cular   contraction    with     the     indications 
furnished  by  the  signal  of  Marcel   Depretz 
put  in  action  directly  by  the  muscle,  while  another  signal  marked  the  moment 
of  the  excitation,  and  the  vibrating  style  of  a  chronograph    recorded  the  ^5-i^ 
of  a  second. 

Further,  this  author,  instead  of  two  observations,  made  three,  by  stimulating 
the  nerve  in  three  different  i)oints.  The  comparison  of  the  times  with  the  space 
traversed  leads  him  to  conclude  that  the  rate  of  propagation  of  the  impulse  is 
not  uniform,  but  continually  changes  during  its  transmission  through  the  nerve. 

C.    STIMULATION  OF  NERVES 

Stimulation  is  a  communication  of  an  external  movement  to  our 
own  tissues.  It  must  be  added  that  this  communication  belongs  to 
the  order  of  shocks  or  of  rupture  of  equilibrium  ;  the  movement,  once 
induced,  continuing  by  the  expenditure  of  a  pre-existing  potential. 
In  this  phenomenon,  which  is  known  as  excitation,  there  is  then  a 
movement-cause  (coming  from  the  exterior)  and  a  movement-effect 
(internal  to  the  stimulated  tissue).  Usually  this  last  greatly  exceeds 
the  first  in  magnitude  ;  this  being  so  because  it  is  divided  into  two 
effects,  of  which  one  is  strictly  the  work  of  rupture  or  of  shock  (equal- 
ling the  exciting  work)  ;  while  the  other,  secondarily  evolved,  is  a 
measure  of  the  liberated  potential  energy. 

Gradation  of  the  effects. — In  order  that  the  effects  of  the  stimulation 
may  have  free  play,  the  exciting  cause  must  attain  a  certain  intensity, 
below  which  it  is  either  inefficacious  or  insufficient.     This  degree  of 


THE  NERVOUS  ELEMENT  51 

energy  corresponds  to  what  is  known  as  the  7ninimum  excitation,  or 
the  threshold  of  excitation.  If,  starting  from  this  degree  of  intensity, 
the  force  of  the  stimulation  varies,  two  things  may  happen.  In  certain 
cases,  as  in  the  muscle  of  the  heart,  the  effect  is  not  increased.  In 
many  other  cases  there  is  a  certain  relationship  between  the  intensity 
of  the  stimulation,  or  that  of  the  shock,  and  that  of  the  effect  produced. 
The  response  of  the  stimulated  tissue  progressively  increases,  and 
attains  a  maximum  which  cannot  be  exceeded  :  this  is  the  maximum 
excitation.  At  the  precise  moment  at  which  it  attains  this  maximum 
the  excitation  is  optimum,. 

If  the  excitant  still  increases  in  intensity  a  contrary  phenomenon, 
diminution,  results  :  there  is  a  decrease  of  the  effect  produced,  which 
may  proceed  to  its  complete  annihilation  :  this  is  the  excitation  known 
as  pessimum. 

All  tissues  are  excitable  ;  certain  of  them,  like  the  nerve  tissue,  are 
so  to  a  high  degree,  and  are  organized  in  such  a  way  as  to  be  capable 
of  transmitting  and  communicating  their  stimulation  to  other  tissues. 
A  muscle  supplied  with  its  nerve  (in  practice  a  frog's  foot  whose  nerve 
trunk  has  been  isolated  :  galvanoscopic  foot)  is  the  most  convenient 
subject  for  the  study  of  stimulation  and  of  its  laws. 

Various  stimuli. — Stimuli  may  be  of  very  different  natm-e.  Some  are  natural  : 
light  for  the  retina,  sound  for  the  internal  ear,  the  energy  whose  nature  is  un- 
known by  which  the  motor  nerve  acts  on  the  muscle  .  .  .  are  of  this  order  ; 
each  of  these,  in  the  circmnstances  peculiar  to  itself,  reacts  on  an  apparatus  which, 
in  the  course  of  phylogenetic  and  ontogenetic  development,  becomes  adapted  to 
this  stimulus  rather  than  to  any  other.  Others  are  artificial  :  mechanical 
shocks,  electricity,  chemical  agents  ...  by  attacking  each  one  of  the  preced- 
ing organs  they  will  elicit  its  special  reaction,  although,  in  the  exercise  of  the 
functions  of  any  one  of  the  organs,  these  agents  take  no  part  whatever.  The 
same  facts  may  be  expressed  in  other  words  if  we  say  that,  of  these  excitants, 
the  first  are  specific,  that  is  to  say,  display  an  adaptation  of  evolution,  while  the 
second  are  general,  that  is  to  say,  manifest  a  common  property,  or  a  property 
coimnon  to  all   protoplasm,  that,  namely,  of  reacting   to  external  stimulation. 

Electrical  stimulation. — Amongst  the  artificial  excitants,  electricity  is  that 
which  is  most  convenient  for  the  general  study  of  the  laws  of  excitation.  Pres- 
sure or  mechanical  shock,  even  when  very  slight,  may  stimulate  the  motor  or 
sensory  nerves,  and  this  means  was  much  employed  when  experiments  for  the 
determination  of  nervous  functions  were  first  iindertaken.  Certain  weak  chemi- 
cal substances,  such  as  glycerine,  chloride  of  sodixmi  .  .  .  may  also  act  as 
stimulants  ;  but  the  rapidly  destructive  effects  of  these  stimuli  and  the  difficvdties 
which  attend  their  graduated  employment  much  limit  their  use. 

PRELIMINARY  IDEAS 

It  becomes  more  and  more  necessary  for  the  physiologist  and  for  the  physician 
to  be  acquainted  with  the  language  of  electrology  and  to  be  familiar  with  the 
exact  signification  of  the  ordinary  terms  made  use  of  in  this  science,  which  is 
more  and  more  appealed  to  as  a  means  for  the  study  of  living  beings. 


52  ELEMENTARY  NERVOUS  FUNCTIONS 

A.  Electrical  Energy — Its  Units 

Potential  energy. — Metapliorieally  speaking,  potential  energy  may  be  defined 
as  a  difference  of  level.  Two  mill  courses,  two  lakes,  of  which  the  upper  levels 
are  at  a  different  height  above  the  level  of  the  sea,  present  a  difference  of  poten- 
tial ;  if  they  are  united  by  a  conducting  pipe  at  their  inferior  level,  a  motor  force 
of  running  water  comes  into  action,  being  so  much  the  stronger  as  the  difference 
of  level  is  greater.  Two  metallic  isolated  spheres,  equal  in  size,  imequally  charged 
with  electricity  and  united  by  a  conductor,  will,  in  the  same  way,  give  rise,  in 
this  conductor,  to  an  electric  cvirrent. 

Electro -motive  force. — Electro-motive  force  thus  originates  in  a  difference  of 
electrical  potential  between  two  given  points  on  the  conductor.  The  absolute 
value  of  this  potential  is  not  taken  into  account,  any  more  than  the  absolute 
level  of  the  jars  in  communication,  but  only  the  difference  between  two  given 
values.  In  the  case  of  reservoirs  full  of  water,  the  zero  potential  would  be  the 
sea  :  for  the  water  of  lakes  and  of  reservoirs  of  all  kinds  runs  away  into  it  until 
it  is  exhausted,  if  they  are  fm"nished  with  deep  conducting  pipes  and  if  the  water 
is  not  renewed.  As  regards  bodies  charged  with  electricity,  the  zero  potential 
is  the  earth  :  every  body  electrically  connected  to  the  earth  loses  its  potential 
if  its  charge  is  not  renewed. 

Its  unit  :  the  volt.  —  The  difference  of  potential  between  two  points  of  a 
channel  of  water  is  measured  in  metres  or  fractions  of  a  metre  (reckoned  verti- 
cally) ;  the  difference  of  potential  between  two  points  of  an  electric  conductor 
is  estimated  in  volts.  The  volt  is  the  unit  of  electromotive  force  ;  it  is  equal  to 
the  difference  of  potential  existing  betw^een  the  two  poles  of  a  Daniell's  element. 
Unit  of  resistance  :  the  ohm. — A  force  which  is  conveyed  in  canals,  from  the 
mere  fact  of  its  canalization,  experiences  a  resistance  wdiich  transforms  it  par- 
tially into  heat,  and  which  economizes  its  expenditure  to  a  greater  or  less  extent. 

/  For  a  given  conductor  (electric  or  not), 
the  resistance  will  be  so  much  the  stronger 
as  its  length  is  greater  and  its  section 
narrower.  The  unit  of  electric  resistance 
is  the  oJmi  ;  practically  it  is  equal  to  that 
of  a  wire  of  annealed  copper  50  metres 
long  by  1  millimetre  in  diameter. 

The  converse  of  the  resistance  is  known 
as  the  conductivity  ;    it    is  so    much    the 
greater  as  the    condvictor    is    shorter  and 
Fig.   24. — Resistance   coil  or  rheostat,     its  section  is  larger. 

The  resistance  increases  in  proportion  as  Unit  of    Intensity  :   The    Ampere. — The 

the  keys  1,  2,  3,  4  are  removed.  intensity    of    a    current    of    water    is    its 

yield  (the  quantity  which  flows  in  a  unit  of  time)  ;  this  yield  is  proportional  to 
the  difference  of  potential  (difference  of  pressm-e,  motive  force)  ;  it  is  inversely 
proportional  to  the  resistance,  or  directly  proportional  to  what  may  be  called 
the  conductivity  of  the  conduit.  If  there  were  no  other  available  means  of 
more  easily  measuring  it,  it  could  be  expressed  by  a  relation  between  these 
quantities. 

Law  of  Ohm. — The  electric  yield,  or  intensity  of  the  current,  is  necessarily 
expressed  by  this  same  relation. 

Let  I  be  the  intensity,  E  the  electromotive  force  and  R  the  resistance  ;  then 
this  equation  arises  : 

R 

If  E  is  made  equal  to  1,  that  is  to  say  an  electromotive  force  about  equal  to  a 


THE  NERVOUS  ELEMENT  53 

Daniell's  cell,  and  Rz:=l,  that  is  to  say  a  resistance  equal  to  1   ohm,  the  unit  of 

intensity  is  determined,  that  is  to  say  the  ampere 

_         1  volt  , 

1   = =  1  anipere. 

1  ohm 

Quantity  of  electricity  :   coulomb. — In  defining  the  intensity  through  the  ratio 

of  the  electromotive  force  to  the  resistance,  the  time  is  left  undetermined.     If 

the  time  is  multiplied  by  the  intensity,  we  arrive  at  the  quantity  :     Q  =  I  x  t, 

and  if  we  assimie  that  the  second  is  an  tinit  of  time,  the  quantity  will  be  the 

amount  of  electricity  spent  when  an  ampere  is  yielded  in  one  second  :    this  is 

the  coulomb  or  ampere-second.     In  commerce  the  ampere-hour  has  been  adopted. 

B.     Different  Electric  Currents — Discharges — Ccrrents  properly 

so    CALLED 

Let  there  be  two  surfaces  of  a  different  potential  ;  when  they  are  united  by  a 
conductor  they  give  rise  to  a  flux  of  electricity  which  is  known  as  a  current.  This 
current  may  assume  different  forms  and  be  of  extremely  different  durations. 

Instantaneous  currents  :  discharges. — If  the  surfaces  carry  charges  which  are 
opposed  or  unequal  and  which  equalize  themselves  by  traversing  a  simple  recti- 
linear conductor,  the  fiux  assunres  an  extremely  rapid  form,  is,  indeed,  practically 
instantaneous  ;  this  is  the  case  with  the  discharges  of  static  electricity.  These 
currents  may  be  usefully  employed  for  the  stimulation  of  nerves  in  conditions 
which  are  correctly  known,  when  condensers  of  a  known  capacity  are  made  use 
of,  to  which  charges  of  a  known  intensity  are  communicated,  and  which  may 
be  directed  through  the  nerve  either  at  their  entrance  into  the  condenser  or  at 
their  exit  from  the  latter,  in  either  direction. 

Continuous  currents. — If  the  surfaces  are  in  contact  with  the  soiu-ce  of  energy 
(chemical,  thermic,  etc.)  which  renews  the  difference  of  potential  as  the  latter 
becomes  weaker,  the  flow  is  then  continuous,  as  in  batteries  and  accumulators. 
The  renewal  of  the  potential  in  proportion  to  its  decline  may  also  be  effected  by 
mechanical  energy,  as  in  Gramme's  machine. 

Constant  current. — A  current  is  called  constant  when  its  value  remains  nearly 
the  same  during  its  passage. 

Polarization. — In  certain  batteries,  of  the  type  of  tliat  of  Volta,  for  example, 
there  arises,  from  the  niere  passage  of  the  current  in  the  interior  of  the  battery, 
a  contrary  electromotive  force  which  is  due  to  the  formation  of  opposing  poles 
by  the  chemical  reactions  and  the  transport  of  the  ions.  The  hydrogen,  set  at 
liberty  by  the  action  of  the  sulphuric  acid  on  the  zinc,  is  borne  to  the  positive 
electrode,  whose  apparent  conductivity  it  diminishes  ;  and,  further,  this  hydrogen 
in  proportion  as  it  increases  in  quantity,  tends  more  and  more  to  reduce  the  zinc 
from  the  sulphate  of  zinc  formed,  whence  arises  the  development  of  an  opposed 
current  contrary  to  tlie  first,  not  so  strong  as  the  latter,  but  whose  intensity 
continues  to  augment  through  the  functional  activity  of  the  cell. 

Non-polarizable  cells. — This  inconvenience  has  been  overcome  by  means  of 
certain  contrivances  which  afford,  in  principle,  to  the  products  formed  during 
the  reaction,  an  iinmediate  point  of  accumulation  by  which  they  are  hindered 
from  being  deposited  on  the  material  which  is  being  destroyed,  so  that  in  this 
way  polarization  is  suppressed  by  arresting  the  action  contrary  to  that  which 
gives  rise  to  the  current.  Thus,  in  Daniell's  cell,  the  hydrogen  formed  by  the 
action  of  sulphviric  acid  on  the  zinc  is  taken  up  to  form  water  (instead  of  reducing 
zinc  from  the  sulphate  of  zinc  which  has  been  formed). 

Accumulators. — ^An  accumulator  is  an  apparatus  constructed  for  the  pm"pose 
of  utilizing  only  the  current  of  polarization,  or  secondary  inverse  cm'rent,  which 
arises  in  cells  after  the  passage  of  their  special  cm-rent,  as  also  in  the  voltameter 


54  ELEMENTARY  NERVOUS  FUNCTIONS 

after  the  passage  of  an  external  cm-rent.  Thus  it  has  been  endeavoiu-ed  by  this 
apparatus  (contrary  to  what  is  aimed  at  in  cells)  to  make  the  polarizing  modifica- 
tion as  marked  as  possible.  Accumulators  are  charged  by  causing  them  to  be 
traversed  by  an  external  current  for  a  certain  time  in  one  direction.  When 
polarization  is  once  produced,  an  inverse  current  of  discliarge  is  received  from  it, 
which  is  remarkably  constant,  and  which  yields  up,  whether  in  quantity  or  in 
energy,  the  greater  part  of  the  electricity  which  it  has  accumulated. 

Like  the  condenser,  the  accmiiulator  is  a  reservoir  of  energy.  In  the  first  this 
energy  is  electric,  in  the  second  it  is  chemical.  In  the  first  it  undergoes  no  essen- 
tial transformation  ;  in  the  second  this  energy  passes,  dm-ing  the  charge,  from 
the  electric  to  the  chemical  state,  and  conversely  during  the  discharge. 

Oscillatory  current. — The  cvirrent,  without  ceasing  to  be  continuous,  may 
present  periodic  augmentations  and  diminutions  of  its  intensity  ;  it  is  then  said 
to  be  osciUatorij. 

Alternating  current. — In  the  electro-magnetic  machines  of  the  class  of  Pixii 
and  of  Clarke  (rotation  of  a  magnet  before  a  current,  or  reciprocally),  the  current 
obtained  presents  not  only  periods  of  augmentation  and  of  diminution,  but  is 
completely  reversed  at  each  half  turn,  unless  by  special  contrivance  this  is 
corrected.  In  both  cases  it  is  oscillatory,  but  when  it  is  not  corrected  it  is 
alternating. 

Sinusoidal  current. — If,  fm-ther,  the  succession  of  values  of  the  current  follows 
the  law  which  regulates  the  oscillation  of  a  pendulum,  the  cm-rent  is  called 
sinusoidal. 

Diphasic,  continuous  and  triphasic  current. — In  the  electro-magnetic 
machines  of  former  days  the  current,  which  is  reversed  at  each  half  rotation, 
presents  two  phases  at  each  complete  rotation  :  it  is  diphasic.  In  Gramme's 
machine  a  special  arrangement  as  regards  the  rolling  of  the  wire  on  the  electro- 
magnet permits  the  production  of  a  continuous  current.  Other  combinations 
of  rolling  allow  the  production  of  triphasic  currents. 

C.     Induction 

Between  two  electrified  bodies  attractions  and  repulsions  arise  which,  when 
they  are  satisfied,  lead  to  displacements  of  these  bodies. 

Lines  of  force  ;  field  of  force.  —  These  displacements  follow  certain  lines 
between  these  bodies,  which  for  this  reason  are  called  lines  of  force.  The  space 
traversed  by  the  lines  is  known  as  the  field  of  force.  These  lines  indicate,  by  their 
number  in  a  given  space,  the  value  of  the  field  in  this  space.  The  field  of  force  is 
said  to  be  so  much  the  larger  as  the  lines  in  it  are  more  closely  compacted  and 
more  mmierous  in  a  given  space.  They  furrow  the  spaces  comprised  between 
electrified  conductors,  and  consequently  pass  through  the  isolating  bodies,  which, 
for  this  reason,  are  known  as  dielectric. 

Electric  induction. — When  a  conductor  (for  example,  a  metallic  sphere)  which 
is  isolated  is  charged  positively  or  negatively,  it  induces,  by  its  lines  of  force,  in 
a  neighbouring  conductor  a  quantity  of  electricity  of  opposite  nature,  which  is 
exactly  equal  to  its  own  :  this  is  static  induction,  or  electric  induction  properly 
so  called,  by  the  lines  of  electric  force. 

Magnetic  induction. — When  a  circuit  conductor  is  traversed  by  a  current,  new 
lines  of  force  are  developed  in  the  space  which  surrounds  it,  each  of  these  forms 
a  closed  circuit  and  each  is  perpendicular  to  the  lines  of  electric  force  or  lines  of 
flow  of  the  current,  and  consequently  perpendicular  to  the  direction  of  the  con- 
ductor which  it  envelops  like  a  ring,  and  creates  in  the  interior  of  the  circuit 
and  around  it  a  field  of  magnetic  force. 

If,  in  this  field,  another  closed  circuit  conductor  is  arranged,  so  that  the 
intensity  of  the  cm-rent  commences  to  differ  in  the  primary  circuit,  the  number 


THE  NERVOUS  ELEMENT 


55 


of  the  lines  of  force  varies  in  the  magnetic  field  ;  this  variation  (positive  or  nega- 
tive), at  the  moment  of  its  production,  induces  a  current  (inverse  in  the  first 
case,  direct  in  the  second)  in  the  secondary  circuit. 

In  the  conditions  which  have  just  been  described,  it  is  the  variable  condition 
of  the  pi'imary  current  which  gives  rise  to  induction  in  the  neighbouring  circuit  : 
during  the  permanent  condition  equilibrium  once  more  prevails.  Induction 
may  be  produced,  but  in  a  different  fashion,  by  increasing  or  diminishing  the 
distance  which  separates  the  circuits.  In  the  one  case,  as  in  the  other,  induction 
ensues  when  tlie  lines  of  magnetic  force  of  the  primary  current  change  their 
number  in  the  secondary  cui^rent. 

Tlie  number  of  lines  of  force  which,  from  the  primary  circuit,  enter  into  the 
secondary  circuit  is  so  much  the  gi*eater  :  (1)  as  the  distance  of  the  two  circuits 
is  shorter  (these  lines  individually  complete  around  the  conducting  wire,  diverge 
more  and  more  as  they  are  removed  from  the  jDlane  in  which  the  circvdt  is  con- 
tained);    (2)  as  the  planes  in  which  the  two  circuits  are   contained  are  more 


Fig.   •25.^^Induction  apparatus  of  du  Bois-Reymond  (after  Waller). 

I,  primary  coil  ;    II,  secondary  coil,  which  inay  be  approximated  to  or  withdrawn  from  the 
former  in  order  to  vary  the  intensity  of  the  induced  current. 

a,  situation  of  the  key  or  interrupter  CL  for  producing  isolated  discharges  ;     b,  situation  of 
key  in  short  circuit  ;  c,  ordinary  arrangement  for  producing  a  series  of  tetanizing  discharges 
d,  another  arrangement  for  modifying  the  relative  intensities  of  the  opening  and  closing  discharges 


nearly  parallel  (wlien  they  are  perpendicular  to  each  other,  no  line  of  force  passes 
from  the  fu'st  to  the  second,  and  there  is  no  induction). 

Solenoids. — A  battery  circuit  is  an  elementary  solenoid,  that  is  to  say,  reduced 
to  a  single  spiral  turn  ;  like  the  solenoid,  it  is  assimilable  to  a  magnet,  but  to 
one  extremely  flattened  out  and  having  a  north  and  a  south  pole  situated,  very 
near  to  each  other,  on  the  axis  of  the  circuit  on  each  side  of  the  plane  which 
contains  it.  Traversed  by  a  ciu'rent  and  free  to  move,  such  a  system  (closed 
battery  floating  on  water)  would  orientate  itself  as  a  magnet,  directing  its 
axis  in  the  magnetic  meridian.  A  solenoid  is  formed  by  an  isolated  conducting 
wire,   rolled   on    itself    a    certain    number   of   times  ;     the    spiral    tvu-ns    form 


56  ELEMENTARY  NERVOUS  FUNCTIONS 

a  series  of  circular  and  spiral  currents.     A  coil,  such  as  that  of  an    induction 
apparatus  or  of  a  galvanometer,  is  a  solenoid. 

Magnet. — A  magnet  may  be  compared  to  a  solenoid  formed  by  molecular 
cvu-rents  orientated  like  that  of  the  spirals  of  a  solenoid  in  a  determinate  manner  ; 
it  is  provided  with  lines  of  force  which,  starting  from  one  pole  (the  north  pole  for 
example),  proceed  to  diverge  in  the  magnetic  field  (siu-rounding  space),  bend 
more  and  more,  and  finally  concentrate  themselves  at  the  opposed  pole  (south 
pole),  then,  returning  in  the  opposite  direction  (from  the  south  to  the  north 
pole)  in  the  interior  of  the  magnet,  complete  the  circuit.  A  solenoid  may  replace 
a  magnet,  and  reciprocally,  in  many  circumstances. 

(a)  Permanent  Magnet. — A  magnet  which  maintains  its  magnetization  (except 
for  slow  loss)  is  called  jDermanent. 

(b)  Temporary  Magnet. — The  superiority  of  the  solenoid  arises  from  the  fact 
that  it  is  possible  to  suppress  or  to  return  to  it  at  will  its  essential  properties,  by 
breaking  or  making  the  electric  current  which  svapplies  it  :  this  is  a  temporary 
magnet. 

(c)  Electro-magnet. — If  in  a  solenoid,  a  rod  of  soft  iron  (or  a  bundle  of  soft  iron 
wire)  is  placed,  the  lines  of  force  are  absorbed  in  large  nmnbers  by  the  metal, 
which  is  magnetically  more  permeable  to  these  lines  of  force  than  is  the  surround- 
ing space  ;  during  the  passage  of  the  current  a  very  powerful  field  of  force  is 
created  as  regards  the  poles  by  the  orientation  of  the  molecular  currents  of  the 
soft  iron  ;  when  the  current  is  broken,  this  arrangement  comes  to  an  end,  and 
the  lines  of  force  disappear.  An  electro-magnet  is  a  temporary  magnet,  but 
more  jDowerful  than  the  ordinary  solenoid. 

Magnetization  and  induction  are  two  very  different  phenomena.  In  magneti- 
zation, there  is  simply  a  special  arrangement  of  currents,  which  circulate,  without 
any  resistance,  in  the  molecules  of  the  steel  (permanent  magnet)  or  of  the  soft 
iron  (temporary  magnet)  ;  these  molecules  play  the  part  of  perfect  conductors. 
In  induction,  at  the  instant  of  augmentation  or  of  diminution  of  the  lines  of 
force  in  the  magnetic  field,  there  is  the  same  impulse  and  movement  of  electricity 
in  the  secondary  circuit  ;  but  this  movement,  arising  in  an  imperfect  conductor, 
is  soon  arrested  by  the  resistance  of  the  circuit  and  ceases  when  the  primary 
current  has  assumed  its  permanent  condition  or  is  itself  arrested. 

D.     Stimulating  Apparatus 

The  electric  waves  which  are  made  use  of  for  stimulation  are  furnished  by 
different  apparatus. 

Condenser. — If  a  nerve  is  electrically  connected,  on  the  one  hand  with  a  charged 
condenser,  on  the  other  with  the  earth,  the  floiv  of  the  discharge  i^roduces  a  wave 
capable  of  stimulating  it.  It  may  also  be  stimulated  by  placing  it  in  the  floiv 
of  discharge.  The  discharge  and  the  charge  form  two  waves  which  are  nearly 
equal  in  intensity  and  duration.  There  are  different  means  of  causing  these 
two  conditions  to  vary,  but  the  shape  of  the  wave  is  not  well  knowTi. 

The  charge  and  the  discharge  depend  on  the  resistance  R,  on  the  capacity  C 
and  on  the  self-induction  L  of  the  line. 

For  R  :^  ^    /  —    -   the  discharge  is  contmuous. 

\/       C 

For  R  <  .    / „  ,,  „  oscillating. 

With  ordinary   wires   which  are  not   rolled  up  self-induction    is    a    negligible 
quantity. 

Induction  apparatus.— The  induced  current  which  takes  origin  in  the  secondary 
coil  of  the  apparatus  of  du    Bois-Reymond  is  very  usually  employed  for    the 


THE  NERVOUS  ELEMENT 


57 


purpose  of  electrical  stimulation.  The  two  induced  currents,  the  one  inverse 
on  closing  the  circuit,  the  other  direct  on  opening  it,  are  equal  in  quantity, 
but  inversely  unequal  in  diu-ation  and  intensity.  Self-induction  considerably 
prolongs  the  fii'st,  especially  if  a  rod  of  soft  iron  is  placed  in  the  coil.  The  in- 
tensity is  graduated  (but  imperfectly)  by  causing  the  distance  of  the  two  coils 
to  vary  on  a  graduated  scale.  The  intensity  of  the  induced  current  decreases 
as  the  square  of  this  distance. 

Batteries  ;  accumulators. — Practically  there  is  scarcely  any  means  which  is 
at  the  same  time  eas\-  and  correct  of  eliminating,  in  a  continuous  ciu'rent,  waves 
of  the  character  of  those  which  will  be  described  farther  on  in  connexion  with 
the  law  of  excitation.  The  wave  of  making  tlie  current  is  made  use  of,  and  also 
that  of  cessation  (breaking  of  cm-rent).  The  action  of  the  second  is  gi'eatly 
complicated  by  the  effects  (electrolytic  amongst  others)  which  are  due  to  the 
passage  of  the  current. 

Rheotomes. — In  order  to  make  or  break  the  current,  different  apparatas  may 


Fig.  26. — Rheotome  of  Bernstein  (application  of  the  method  of  Guilleniin). 

A  rod  wliich  carries  a  contact  1  closes  periodically  (by  a  rotatory  movement  of  the  axis  which 
supports  it) — a  battery  circuit  inducing  a  cui'i-ent  which  stimulates  the  nerve. — Fui'ther,  another 
contact  2  (in  the  shape  of  a  bridge)  closes,  in  a  galvanometer,  another  circuit,  in  which  the 
muscle  is  included,  and  allows  of  the  determination  of  the  electromotor  phenomena  which  arise 
in  the  latter  from  the  fact  of  stimulation. 

The  contacts  1  and  2  may  be  mutually  displaced  so  that  (for  a  given  rate  of  rotation)  the 
interval  of  time  which  separates  them  may  be  increased  or  diminished.  In  this  way  the  direction 
and  the  successive  intensities  of  the  electromotor  phenomenon  wliich  is  developed  in  the  muscle 
in  the  period  succeeding  the  stimulation  may  be  studied. 

be  made  use  of,  oscillating  pendulmns  (Chauveau),  contacts  effected  by  a  rotatory 
movement  (Bernstein),  which  bring  about  these  closings  and  openings  of  the 
circuit  at  equal  intervals  and  at  the  same  rate. 


E.   Apparatus  for  the  Estimation  and  the  Measurement  of  Electromotive 

Phenomena 

Galvanometers  and  electrometers  are  employed,  chiefly  the  electrometer  of 
Lippmann. 


58 


ELEMENTARY  NERVOUS  FUNCTIONS 


Galvanometers. — Two  cui'rents,  two  solenoids,  two  magnets,  one  solenoid  and 
one  magnet  are  capable  of  reacting  the  one  upon  the  other.     If  one  is  fixed  and 

the  other  movable,  when  the  current  passes 
through  the  solenoid  displacements  ensue  which 
may  be  made  use  of  to  prove  the  existence  of 
such  a  current,  to  determine  its  direction  and  to 
estimate  its  intensity. 

Electrometer  of  Lippmann. — This  consists  of  a 
tube  ending  in  a  conical  capillary  point  ;  it  is  filled 
wdth  mercury,  and  dipped  in  a  solution  of  sulpliuric 
acid  which  itself  rests  on  mercury  ;  when  this  ap- 
paratus is  traversed  by  a  current,  the  capillary 
constant  is  changed  and  the  mercury  is  displaced 
in  the  conical  point  to  a  certain  extent  which  varies 
according  to  the  direction  of  the  current.  The 
amount  of  the  displacement  (within  certain  limits) 
indicates  tlu-  difference  of  the  potential. 

Non-polarizable  electrodes.  —  The  contact  of 
metallic  wires  with  the  tissues  gives  rise  to  polar- 
izations which  set  up  contrary  currents  capable 
of  seriously  invalidating  observations.  These 
difficulties  may  be  avoided  by  making  use  of 
non-metallic  electrodes,  which  are  almost  incajDable 
of  polarization. 


Fig.  27. — Diagram  of  an  as- 
tatic galvanometer. 

The  current  brought  to  the 
two  terminals  t,  t  is  conveyed  by 
a  wire  which  is  rolled  succes- 
sively and  in  contrary  directions 
round  two  conjoined  magnets 
sn  and  ns,  forming  a  movable 
suspended  arrangement.  The 
upper  magnet  carries  a  mirror 
on  which  a  luminous  ray  is  re- 
flected, forming  an  image  on  a 
graduated  scale — the  displace- 
ment of  the  image  measures  the 
intensity  of  the  current. 

N  S,  fixed  magnet  intended  to 
give  a  position  of  repose,  which 
can  be  varied  at  pleasure,  to  the 
two  others. 


D.    LAWS  OF  ELECTRIC  STIMULATION 


1.  The  problem  to  be  resolved. — Elec- 
tricity acts  as  a  stimulus  on  every  excitable 
organ,  especially  on  a  nerve  when  it  passes 
through  it  in  the  form  of  a  current,  whatever 
may  be  the  nature  of  this  latter.  It  only 
exerts  its  stimulating  and  impulsive  effect 
so  far  as  it  is  itself  in  movement. 

A  current  has  of  necessity  a  period  of 
inauguration  {a  variation  ivhich  is  more  or 
less  rapid  in  its  intensity  starting  from  zero), 
a  phase  of  persistence  in  certain  conditions  (constancy  of  the  cur- 
rent), a  phase  of  cessation  (of  more  or  less  rapid  variation  the  converse 
of  the  first). 

It  has  at  every  instant  a  determinate  intPMsity;  it  has  a  total  duration; 
it  represents  a  quantity  of  electricity  supplied,  and  it  represents  an 
energy  expended.  Which  of  these  factors  takes  part  in  the  stimulation 
in  an  exclusive  or  preponderant  manner  ? 


Historical  ;  facts  and  opinions. — Tliese  questions  have  offered  themselves  for 
solution  from  the  very  commencement  of  methodical  studies  concerning  the 
effects  of  electricity  on  the  nerves  and  other  excitable  tissues.  The  researches 
commenced  by  a  work  of  du  Bois-Reymond  (1848). 


THE  NERVOUS  ELEMENT 


59 


Experiment. — A  nerve  is  traversed  by  a  cvu'rent  ;    at  the  making  of  the  latter 
a  contraction  of  the  muscle  ensues  ;    duing  the  passage,  the  organ  remains  in 


Fig.  28. — Reflecting  Galvanometer  with  its  scale  for  reading  the  deviations. 
A  sliunt  is  interposed  between  the  galvanometer  and  the  soiu-ce  of  the  current  to  be  measured . 

repose  ;  at  the  breaking  of  the  ciu'rent,  there  is  once  more  a  contraction.    Another 
fact  of  the  same  kind  :    a  nerve  is  included  in  the  circuit  of  a  battery  (by  the 


Fig.   29. — Capillary  electrometer  of  Lippmann. 

On  the  left,  the  apparatus  as  a  whole  ;  in  the  middle,  diagram  of  the  apparatus  ;  capillary- 
tube  full  of  mercury  phuiged  into  a  solution  of  sulphuric  acid  resting  on  a  layer  of  mercury. 
On  the  right,  appearance  of  the  capillary  column  at  its  extremitj^  seen  in  the  microscopic  field. 


60 


ELEMENTARY  NERVOUS  FUNCTIONS 


aid  of  a  rlieocord)  ;  tlie  intensity  of  the  current  is  caused  to  vary  slowly,  so  that 
its  strength  may  be  greatly  increased  :  there  is  no  stimulation  ;  but,  if  a  sudden 
variation  is  caused  in  the  intensity  of  the  current,  there  is  contraction. 

2.  Old  formula. — From  this  du  Bois-Reymond  has  concluded  that 
it  is  not  the  absolute  value  of  the  intensity,  but  the  variation  of  the  intensity 
of  the  current  ivhich  causes  the  stimulation  ;  in  other  words  :  if  two 


Fig.   30. — Xon-polarizable  electrodes  for  receiving  the  currents  of  muscles  or   nerves. 

1  and  2,  those  of  du  Bois-Reymond  ;  3,  those  of  Burdon-Sanderson  ;  4,  those  of  V.  Fleischl ; 
5,  those  of  d'Arsonval. 

The  metallic  wire,  contact  of  which  with  the  living  tissues  must  be  avoided,  is  plunged  into 
a  tube  filled  with  a  solution  of  a  salt  of  the  same  metal  (zinc  in  sulphate  of  zinc,  copper  in  sulphate 
of  copper).  The  extremity  of  the  tube  is  closed  by  a  stopper  of  kaolin  impregnated  with  a 
neutral  solution  of  chloride  of  sodium  and  is  of  form  suitable  for  application  to  the  nerve  or  the 
muscle. 

identical  nerves  are  traversed  by  two  currents  /  and  /i  which  differ 
considerably,  and  if  these  two  different  currents  are  made  to  increase 
or  decrease  by  the  same  quantity,  during  the  same  time  and  in  the 
same  manner,  the  two  nerves  will  be  equally  stimulated.  The  stimu- 
lation will  be  so  much  the  greater  as  the  variation  dl  in  the  unit  of 
time  is  greater,  that  is  to  say,  the  variable  period  is  more  rapid,  the 
wave  shorter. 

Contradictory  facts. — It  was  thought  at  first  that  the  experimental  fact  on 
which  this  theory  of  stimulation  is  based  was  of  general  application.  In  reality 
this  is  not  the  case.  In  operating  on  other  animals,  it  may  be  found  wanting. 
Grutzner  (1887)  has  observed  that  the  motor  nerve  of  the  toad  responds  better 
to  slow  and  prolonged  variations  of  the  current  than  to  those  which  are  rapid. 
Fick  finds  that,  even  in  a  frog,  a  muscular  response  is  not  elicited  when  the  passage 
of  the  wave  is  of  very  short  duration.     Brucke  finds  that  it  is  the  same  as  regards 


THE  NERVOUS  ELEMENT  61 

curarized  nerves,  so  long  as  the  poisoning  lasts.  Pflliger  observes  that  nerves 
react,  in  certain  conditions,  even  to  a  constant  current.  Hence  it  cannot  be 
admitted  that  the  variation  of  intensity  is  the  sole  and  only  factor  of  the  stimu- 
lation. 

Cybulski  and  Zanietowski,  as  also  Waller,  consider  that  the  important  factor 
is  the  electrical  energy.  But  Boudet  (of  Paris)  had  previously  found  that  "  the 
same  ciuantity  of  electrical  energy  expended  did  not  ahva\-s  produce  the  same 
effect." 

Fick  (1869)  and  Wertheim-Salomonson  attribute  a  direct  influence  on  the 
magnitude  of  the  reaction  to  the  quantity  of  electricitj^  but  Avithout  regarding 
it  as  the  sole  factor  in  stimulation. 

G.  Weiss  (1901)  has  re-investigated  the  subject  by  the  aid  of  very  exact 
methods,  and  he  proves  that  the  rnxantity  of  electricity  made  use  of  is  the 
important  factor  in  electrical  stimulation. 

3.  Conditions  which  must  be  observed  ;  method. — A  wave  of  a  simple 
form  must  be  capable  of  being  projected  into  a  nerve,  and  the  duration, 
as  also  the  intensity  of  this  wave,  must  be  exactly  kno\^  n.  Acquainted 
with  the  duration,  as  well  as  with  the  intensity,  it  will  be  possible,  in 
the  preliminary  discussions,  to  determine  the  threshold  of  excitation, 
that  is  to  say,  the  intensity  which,  for  a  given  duration,  is  just  sufficient 
to  cause  a  contraction.  Having  thus  determined  the  wave  which 
gives  the  threshold  of  excitation,  an  abbreviation  of  this  is  effected 
in  such  a  manner  as  to  reduce  somewhat  its  duration,  thus  forming 
two  waves  of  a  total  duration  which  is  less  than  that  of  a  standard 
wave.  Contraction  no  longer  .  results  (or,  the  conditions  being  the 
same,  in  order  to  obtain  it,  the  voltage  must  be  increased).  If  the 
stimulation  were  due  to  the  variation  of  the  potential,  conformably 
to  the  hypothesis  of  du  Bois-Reymond,  contraction  should  have  taken 
place.  If  two  waves  of  a  total  duration  equal  to  that  of  the  standard 
wave  are  projected  into  the  nerve,  contraction  follows. 

Result. — Thus  it  is  clearly  seen  that,  in  every  case,  it  is  the  quantity 
of  electricity  which  is  here  the  important  factor,  and  not  the  energy,  for 
the  latter  may  be  equal  for  a  lesser,  or  greater  for  an  equal  quantity, 
without  any  change  in  the  results. 

Apparatus. — For  the  purpose  of  having  at  command  an  electric  wave  of  a 
known  intensitj^  and  duration  which  has  been  accurately  determined,  the  major- 
ity of  the  apparatus  employed  (condensers,  induction  coils,  etc.)  are  worthless. 
G.  Weiss  has  invented  the  following  arrangement,  which  is  altogether  satisfac- 
tory. 

(a)  Estimation  of  the  Duration. — The  nerve  is  interpolated  in  the  circuit  of  a 
constant  battery.  This  circuit  contains  a  derivation  of  a  relative  resistance 
such  that  (as  regards  the  wires  going  to  the  nerves),  all  being  entirely  closed, 
the  nerve  receives  no  appreciable  quantity  of  electricity.  If,  then,  the  derivation 
is  broken  at  a  point,  the  ciu-rent  passes  into  the  nerve  ;  if  the  interruption  occurs 
at  a  second  point,  this  time  in  the  circuit,  the  ctu'rent  ceases  to  pass,  the  wave  is 
finished.     Its  duration  is  measured  by  the  time  which  elapses  between  the  two 


62  ELEMENTARY  NERVOUS  FUNCTIONS 

interruptions.  These  interruptions  are  effected  by  the  ball  of  a  carbine 
worked  by  liquid  carbonic  acid,  whose  rate  is  130  metres  a  second  (at  the 
temperature  of  the  laboratory). 

The  interval  between  the  two  interruptions  depends  on  the  distance  between 
the  wires,  the  latter  being  placed  parallel  to  one  another  in  the  plane  of  transit 
of  the  ball.  For  an  interval  of  one  centimetre,  the  duration  of  the  wave  will  be 
O'<^^000077,  etc. 

By  making  the  arrangement  more  complicated,  several  successive  waves  may 
be  obtained  having  definite  durations,  succeeding  one  another  at  definite  intervals 
of  time,  so  that  tlie  comparisons  and  controls  indicated  above  may  be  effected. 
Such  is  the  mode  of  estimating  the  duration  of  the  wave. 

(b)  Estimation  of  the  Intensity. — To  calculate  the  intensity,  the  voltameter  is 
connected  with  the  terminals  of  the  battery  or  the  distributer  of  the  potential. 
This  voltameter  registers  a  figure  proportional  to  the  intensity  of  the  current, 
since  in  the  successive  experiments  the  resistance  of  the  circuit  does  not  vary 
(E  ^  IR  ;  E^  =  I^  R  ;  EE^is  proportional  to  //). 

If  the  value  of  current  is  not  determined  with  absolute  precision,  yet  it  is  so 
within  very  narrow  limits. 

(c)  Ratio  of  the  Energy  to  the  Quantity. — The  energy  of  the  current  is  expressed : 

Elt  =  EH  X  R. 
It  is,  as  a  constant  factor,  nearly  W  =  E'-t. 
The  quantity  of  electricity  employed  is  Q  =  It  =  Et  x  R. 
It  is,  as  a  constant  factor,  nearly  Q  =  Et. 

It  is  seen  that  the  quantity  of  electricity  varies  as  E,  while  the  energy  varies 
as  its  square,  E  ". 

For  a  given  duration  the  quantity  remains  constant. — Thus  the  first 
stage  of  the  argument  is  estabhshed.  For  a  given  yeriod  of  time,  in 
order  to  obtain  the  threshold  of  excitation,  the  same  quantity  of  electricity 
is  required.  If  this  necessary  quantity  is  not  supphed  to  the  nerve, 
the  minimum  excitablHty  is  raised.  This  minimum  is  so  much  the 
more  elevated  as  the  frequency  of  the  wave  is  greater,  that  is  to  say, 
shorter.  When  the  frequency  is  sufficiently  great,  very  high  voltages 
may  be  employed  without  attaining  the  threshold  of  excitation. 

The  threshold  of  excitation  implies,  for  a  given  duration,  a  given  ciuantity  of 
electricity.  Supposing  that  the  duration  varies,  will  this  quantity  remain  fixed 
or  will  it  vary,  and  if  so,  how  ? 

Variation  of  the  quantity  as  a  function  of  the  duration, — From  the  formtda 
Q  =  Et  it  is  obvious  that  a  quantity  of  electricity  remains  the  same  if  its  two 
factors,  intensity  and  duration,  undergo  proportionally  inverse  modifications. 
Will  the  same  threshold  of  excitation  be  maintained  if  t  and  E  are  modified  in- 
versely, in  such  a  manner  as  to  preserve  Q  equal  to  itself  ?  Experience  tells  us 
that  this  is  not  so. 

In  proportion  as  tlie  duration  t  augments,  the  Cjuantity  Q  augments  equally. 
This  shows  that  the  quantity  Q  represents  the  svim  of  two  terms,  the  one  fixed, 
which  may  be  described  as  A,  the  other  B,  proportional  to  the  duration  of  the 
excitation.  Hence  the  quantity  required  to  produce  the  excitation  becomes  : 
Q  ^  A  X  Bt. 

In  order  to  prove  this,  a  series  of  initial  stimuli  are  applied  to  the  same  nerve 
in  identical  conditions,  the  waves  being  of  variable  duration  but  not  exceeding 
^sec  Q()23,  while  at  the  same  time  in  each  case  the  quantity  of  electricity  is 
measured.     The  duration  of  the  wave  (time  of  stimulation)  is  represented  by 


THE  NERVOUS  ELEMENT 


63 


abscissfB  ;  the  quantity  of  electricity  employed  is  expressed  in  ordinates.  Thus 
is  obtained  a  straight  line  which  does  not  pass  tlirough  the  origin.  It  represents 
the  quantity  of  electricity  which  is  required  for  the  minimum  excitation  of  the 
nerve  expressed  as  a  function  of  the  duration  of  the  stimulation. 

4.  Law  of  electrical  stimulation. — The  researches  of  G.  Weiss  ex- 
plain the  paradoxical  facts  of  Grutzner,  of  Brucke,  and,  further,  thej^ 
lead  to  a  general  la\\'  which  is  applicable  at  the  same  time  to  the  more 
prompt  reaction  of  the  nerve  of  the  frog.  This  is  in  accord  with  the 
results  of  Dubois  (of  Berne)  and  of  Horweg,  which  were  obtained  in 
making  use  of  the  condenser.  The  law  may  be  thus  expressed  :  In 
order  to  obtain  the  initial  response  of  a  nerve  or  of  a  muscle,  electrical 
stimulation  must  make  use  of  a  constant  quantity  of  electricity  ;  and, 
further,  this  quantity  must  be  jyroportional  to  the  duration  of  the  discharge. 


"       Buttery 


Rheocord 


Commutator 


Bheotome 


Myograph 


Fig.   31.— Arrangement  for  the  stimulation  of  nerves. 
Action  of  the  constant  current. 


According  to  this  observer,  "  everything  tends  to  prove  that  a  con- 
stant cj^uantity  of  electricity  is  necessary  in  order  to  stimulate  a  nerve, 
but  that  it  is  also  necessary,  during  the  whole  of  the  operation,  to  cease- 
lessly oppose  a  process  of  return  to  the  first  state  by  means  of  another 
quantity  of  electricity  which  is  proportional  to  the  duration  of  the 
action." 

5.  Methods  of  stimulation. — In  order  that  the  nerve  may  be  stimu- 
lated by  a  current,  matters  are  so  arranged  that  the  nerve  forms  part 
of  the  circuit  traversed  by  this  current,  at  least  for  a  small  portion  of 
its  length. 


G4 


ELEMENTARY  NERVOUS  FUNCTIONS 


According  to  circumstances,  two  arrangements  are  made  use  of.  In 
the  one  the  isolated  nerve  is  placed  in  contact  with  the  two  electrodes, 
which  are  situated  at  a  certain  distance  the  one  from  the  other.  The 
lines  of  passage  of  the  current  follow  the  direction  of  the  nerve  as  in  a 
regular  cylinder  ;  the  density  of  the  current  is  the  same  at  its  entrance, 
at  its  exit  and  in  the  intervening  space  :  this  is  the  bipolar  method.  In 
the  other,  the  nerve,  usually  superficial,  but  adherent  to  the  mass  of 
subjacent  tissues,  is  in  contact  (often  through  the  skin)  with  one  of  the 
two  poles,  the  other  pole  being  placed  at  some  distance. 

The  lines  of  transmission,  if  the  positive  pole  is  on  the  nerve,  diverge 


Position  of  the 
myo'jrftph  for  ch'irge     ~ 
and  discharge 

Fig.   32. — Arrangement  for  the  stimulation  of  nerves. 

Action  of  the  charge  and  discharge  of  the  condenser. 


from  the  point  of  contact  in  every  direction  and  proceed  to  complete 
the  current  at  the  other  pole  ;  or,  if  the  negative  pole  is  on  the  nerve, 
converge  parallel  to  the  nerve  starting  from  the  positive  j3ole  :  this  is 
the  monopolar  method. 

Polar  influence. — This  second  arrangement,  designed  and  recom- 
mended by  Chauveau,  shows  in  a  very  definite  manner  the  different 
action  of  the  two  poles.  Let  it  be  assumed  that  the  two  electrodes  are 
symmetrically  placed  on  two  similar  nerves,  as  the  two  facial  nerves 
in  mammals  or  the  sciatic  nerve  in  the  frog,  and  let  the  current  be  pro- 
jected alternately  in  the  two  directions.  As  the  intensity  of  the  current 
increases  from  zero,  the  first  contraction  will  occur  in  connexion  with  the 
negative  ])ole,  whether  it  is  on  the  right  or  on  the  left,  while  the  muscle 
in  contact  with  the  positive  pole  will  remain  in  repose.  When  the 
strength  increases,  starting  from  this  point,  a  new  threshold  of  excitation 
arises  for  the  positive  jjole  ;   then  the  contractio7is  become  equal  ;    later. 


THE  NERVOUS  ELEMENT 


65 


those  at  the  positive  pole  become  'predominant,  irhile  those  at  the  negative 
pole  tend  to  diminish.  Finally,  according  to  Boudet  (of  Paris),  if  the 
intensity  still  increases,  the  contractions  at  the  positive  pole  diminish 
in  their  turn,  once  again  become  equal  to  those  at  the  negative  pole, 
then  diminish  more  rapidly  than 
these  last,  and  cease  before  them. 

The  effects  due  to  each  of  the  two 
poles  may  be  represented  by  two 
curves,  the  one  more  extended  and 
more  elliptical  (negative  pole),  the 
other  shorter  and  with  a  still  higher 
summit  (positive  pole)  which  present 
two  points  of  intersection. 

Active  pole  ;  indifferent  pole. — 
In    electro-therapeutics,     it     is    not 


1 

-> 

f. 

K 

^^ 

■'-^^ 

N 

X 

/^ 

P 

/ 

1 

2 

3      ' 

4- 

5 

5 

7 

3 

i     1 

0 

1      12 

Fig.      34. — Inequality     of    the     polar 
actions  (after  Boudet,  of  Paris). 

The  effects  of  closing  and  opening  are 
examined  separately  in  two  experiments. 
XI  'S-,  negative  pole  ;  Pi  P2,  positive 
pole. 

The  electromotor  force  of  the  current 
increases  from  1  to  24  volts. 


Fig.   33. — Inequality  of   the  polar  actions  of 
the  ciu-rent  (after  Chauveau). 

N  N,  curve  representing  the  values  •  of  the 
contractions  of  the  negative  pole  on  the  making 
of  the  current.  P  P,  curve  of  the  contractions  of 
the  positive  pole.  Equality  at  the  point  of  inter- 
section of  the  two  cm-ves  ;  inequality  of  opposite 
nature  before  and  after  it.  1,  2  ...  12,  suc- 
cessive intensities  of  the  stimulating  cm-rent. 

generally  necessary  to  stimulate  the  two  nerves  symmetrically  and 
alternately  ;    usually  a  single  nerve  is  alone  treated. 

Thus  the  pole  whose  action  is  rec(uired  is  placed  on  the  nerve,  and  on 
another  locality  situated  at  some  distance,  and  but  little  sensitive,  is 
placed  the  other  pole,  which  is  known  as  indifferent,  and  which  covers  a 
large  surface  (moistened  sponge). 

Cathode  ;  anode. — The  negative  pole  is  usually  known  as  the  cathode 
(in  the  case  of  a  feeble  current  this  is  the  most  active),  and  anode 
describes  the  positive  pole  (in  the  case  of  a  strong  current  this  is  the 
most  active). 

Direction  of  the  current. — In  the  bipolar  method,  the  lines  of  trans- 
mission of  the  current  are  projected,  according  to  the  direction  of  the 
nerve,  alternately  in  two  opposite  directions,  that  is  to  say,  according 
to  the  direction  of  its  conduction  [descending  QurverA)  or  in  the  opposite 
direction  {ascending  current). 

P.  F 


C6  ELEMENTARY  NERVOUS  FUNCTIONS 

The  effects  differ  in  the  two  cases.  Contrary  to  what  might  have 
been  thought,  the  differences  are  not  due  to  an  influence  attributable 
to  the  johysiological  conduction  of  the  nerve,  but  once  again  to  a  polar 
influence.  It  is  seen,  indeed,  that  the  results  are  inverted,  as  above, 
according  to  the  intensity  of  the  current,  and  that  they  follow  funda- 
mentally the  same  law  as  in  monopolar  excitation.  It  is  sufficient,  in 
order  to  recognize  it,  to  remark  that,  in  the  case  of  bipolar  stimulation 
with  the  descending  current,  the  lines  of  flux  have  the  same  orientation 
as  in  monopolar  excitation  with  the  negative  pole  on  the  nerve  ;  and 
the  same  with  the  ascending  current  in  the  bipolar  excitation,  the  same 
also  with  the  positive  pole  in  monopolar  excitation. 


Fig.   35. — Diffusion    of    the    electric    current    in  a    homogeneous  conducting  medium, 
diagram  of  "the  points  of  application  of  the  two  poles. 

The  current  is  completed  by  lines  of  flux  of  which  one  only  is  straight,  the  others  are  inflected 
to  a  greater  or  lesser  extent,  c,  Ci,  Cg,  C3,  and  represent  the  derivations  of  the  current,  feeble  in 
proportion  as  they  are  further  removed  from  the  direct  course. 

These  lines  are  cut  by  the  equipotential  lines  (represented  in  strokes)  +,  +1,  +2,  +3;  — 
— 1>  — 2>  — 3- 

These  lines  connect  the  points  of  the  conducting  medium  having  the  same  potential,  the  same 
positive  tension  to  the  right,  negative  to  the  left  of  a  line  of  zero  potential,  which  cuts  perpen- 
dicularly the  straight  line  uniting  the  two  poles. 

Unipolar  stimulation  in  an  open  circuit. — When  the  two  poles  of  the  stimulating 
circuit  are  placed  on  the  same  nerve,  the  stimulation  is  called  bipolar.  When  a 
single  pole  is  placed  on  the  nerve,  the  other  pole,  covering  a  large  surface,  being 
placed  on  a  remote  region  of  the  animal's  body,  then  it  is  a  case  of  monopolar  or 
unipolar  excitation,  such  as  has  been  recommended  by  Chauveau,  and  is  ordin- 
arily made  use  of  in  electro-therapeutics.  Bvit  a  nerve  may  also  be  stimulated 
in  a  unipolar  manner  by  a  different  method  of  procedure.  For  example,  on 
the  one  hand  the  indifferent  pole,  on  the  other  the  body  of  the  animal  experi- 


THE  NERVOUS  ELEMENT 


67 


mented  on,  may  be  connected  electrically  with  the  earth.  This  method  is  closelj- 
related  to  the  jDreceding  ;  it  differs  from  it  inasmuch  as  the  earth  is  interposed 
in  the  circuit.  Lastly,  after  having  isolated  both  the  animal  and  the  distributer 
of  energy,  communication  may  be  established  through  a  single  pole  with  a  nerve 
of  the  animal,  and  in  this  waj^  again,  motor  effects  may  result. 

The  efficacy  of  this  kind  of  stimulation  which,  at  the  first  glance,  would  appear 
to  be  nil,  is,  as  a  matter  of  fact,  tolerably  great.  In  this  case,  as  in  all  the  others, 
the  stimulation  is  due  to  a  movement  of  electricity  in  the  tissue  [the  nerve)  ivkich  is 
connected  tvith  the  active  pole. 


Fig.  36. — Diagram  showing  the  internal  polarization  of  the  tissues  (after  Waller). 

All  along  the  lines  of  the  flow  of  the  current,  going  from  one    pole  to  the  other,  secondary 
polarities  are  developed  across  the  heterogeneous  portions,  traversed  by  electrolytic  conduction. 


When,  indeed,  an  induction  shock  is  produced,  if  the  induced  current  is  open 
a  more  or  less  large  nmnber  of  electrical  oscillations  are  produced,  whose  frequency 
dejiends  on  several  conditions,  and  more  especially  on  the  capacity  of  the  system 
(Schiller  and  Mouton).  This  frequency  amounts  to  10,000  a  second.  The  cur- 
rents furnished  by  this  miijDolar  stimulation  are  then  alternately  positive  and 
negative,  or  diphasic  currents,  persisting  a  longer  or  shorter  time  according  to 
circumstances. 

A.  ChariJentier  has  methodically  studied  the  action  of  these  special  currents 
{Archives  of  Physiology,  1893-1896). 

Periodic  excitations. — So  far  we  have  assmned  a  simple  stimulation  due  to  an 
isolated  wave.  But,  in  practice,  when,  instead  of  studying  the  laws  of  stimvila- 
tion,  it  is  merely  desired  to  make  use  of  the  latter  in  oi-der  to  demonstrate  the 
fmictions  of  a  given  nerve,  the  excitation  is  prolonged  and  renewed  in  the  nerve 
by  the  passage  of  a  periodical  series  of  similar  waves  which  succeed  one  another 
inverse^.  This  effect  is  realized  by  means  of  the  trembleur  of  du  Bois-Rej^mond's 
apparatus.  These  cm-rents  are  called  tetanizing,  because  the  muscular  contrac- 
tions which  follow  them  in  the  muscle  ai-e  so  close  together  that  they  vmite  them- 
selves in  prockicing  a  physiological  tetanus  by  which  the  tension  of  the  muscle  is 
maintained. 

In  man,  the  object  of  the  stimulation  is  not  the  determination  of  function,  but 
the  forming  of  a  diagnosis  or  the  production  of  a  therapevitic  action  on  the  nerve. 
In  animals  it  is  the  reverse.  In  the  first  case,  the  monopolar  method  is  the  only 
one  applicable,  and  is  very  convenient  ;  in  the  second  the  bipolar  method  is  some- 
times preferable,  becavise  it  permits  of  the  stimulation  being  localized  on  a  given 
nerve.  Usually  the  nerve  has  been  cut  and  is  supported  on  the  electrodes  of 
the  current  by  the  aid  of  a  white  silk  thread  which  is  very  dry  ;  in  this  way  all 
danger  is  averted  of  the  derivation  of  the  cm-rent  to  excitable  parts  other  than 
the  nerve  imder  investigation. 

Remark. — Elsewhere  we  have  assmned  that  the  stimulus  is  applied  to  a  nerve 
element  or  to  a  bundle  of  nerve  elements  of  similar  fmictions,  which  thus  together 
form  a  simple  object.     In  practice  this  is  rarely  the  case.     The  nervous  bimdle 


68  ELEMENTARY  NERVOUS  FUNCTIONS 

which  is  stimvilated  will  frequently  contain  parallel  elements  which  terminate 
in  peripheral  organs  having  distinct  functions,  which  the  excitation  will  to  a 
certain  extent  dissociate  by  revealing  their  presence.  Sometimes,  indeed,  the 
bundle  will  contain  antagonistic  elements,  for  example,  a  mixture  of  motor  and 
inhibitory  elements,  to  such  an  extent  that  the  action  which  ensues  will  be  the 
resultant  of  two  contrary  actions.  The  effect  produced  in  this  case  no  longer 
measures  the  excitability  of  a  given  nerve,  but  sometliing  much  more  compli- 
cated. It  is  probably  for  this  reason  that  the  excitability  of  the  great  sympa- 
thetic and  of  other  analogous  nerves,  that  of  the  tracts  of  the  spinal  cord  and  of 
the  different  portions  of  the  brain,  seems  to  be  less  than  that  of  the  peripheral 
motor  nerves  of  the  skeletal  muscles  ;  these  last  are  the  only  really  simple  nervous 
structures  on  which  we  can  act. 


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70  ELEMENTARY  NERVOUS  FUNCTIONS 

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Atrophy  of  the  spinal  cord  after  amputation. — Berg,  These  Paris,  1896. — Fried- 
lander  et  Kr.auze,  Forscltr.d.  Med.,  1884,  Xo  4. — Hayem  et  Gilbert,  Arch,  physiol. 
norm,  et  path.,  1884,  III,  p.  430. — Marinesco,  Neurol.  Centralbl.,  1892,  p.  463. — Redlich 
Obs.  svir  cobayes,  Centrcdbl.  f.  Nervenheilk.,  1893. — Vanderveld  et  Hemptinne,  Journ. 
med.  Bruxelles,  1893.— H.  Will,  Arch.  f.  Psychiat.,  1895,  XXVII,  p.  585. 

Nervous  suture  ;  reappearance  of  the  functions. — Bachowiecki,  Arch,  f.  microsc. 
Anat.,  t.  XIII,  1876,  p.  420. — Calugareanu  et  Victor  Henri,  Regeneration  fonction, 
nelle  de  la  corde  du  tympan  sutviree  avec  le  bout  central  de  I'hypoglosse,  Biol.,  Janvier 
et  decembre  1901. — Herzen,  Doctrine  de  Schiff,  Rev.  scient.,  1894. — Langley,  Journ. 
of  Physiol.,  1899,  vol.  XXIV. — Laucjier,  C.  R.  Acad,  sc,  20  juin  1864. — Xelaton,  Soc 
de  chir.,  22  juin  1864. — Schiff,  Rec  de  mem.  :  Vanlair,  Assoc,  avanc.  des  sc,  Toulouse, 
1887  ;  Arch.  biol.  de  Van  Beneden,  1893,  t.  XXIIl  ;  Rev.  scient.,  4  aout  1894 ;  Ann.  Soc. 
medico-chirurg.  de  Liege,  1895. 

Regeneration. — Brown-Sequard,  Biol.,  1882. — JVIarinesco,  Biol.,  1894,  p.  389,  et 
nov.  1896. — PiiiLiPEAUx,  Retour  des  fonctions  du  vague  en  trente  jours,  Biol.,  1876. 

Conduction  in  two  directions. — Ajibrosoli,  Schmidt's  Jahrh.  1860,  p.  289. — Arloing 
et  Tripier,  Arch.  f.  Physiol.,  1876. — Babuchin,  Arch.  f.  Physiol.,  Leipzig,  1877  ;  Arch, 
f.  Anat.  unci  Phys.,  1877. — P.  Bert,  Greffe  animale,  Biol.  ;  Soc.  philotn.  ;  These  de  mede- 
cine,  Paris  ;  Journ.  anat.  et  physiol.  ;  Ann.  sc.  nat.  ;  Soc.  des  sc.  de  Bordeaux,  1863  a 
1865  ;  Transmission  dans  les  nerfs  de  sensibilite,  C.  R.  Acad,  sc,  1877. — Bidder,  .  .  . 
lingual  .  .  .  hypoglosse  .  .  .,  Arch,  de  Reichert  et  du.  Bois-Reymond,  1865,  p.  246. — 
Floubens,  Svst.  nerveux. — Gotch  et  Horsley,  Philos.  Trans.,  London,  1891,  vol. 
CLXXXIl,  p!!  485.— Helmholtz,  Monatsb.  d.  Berl.  Acad.,  1894,  p.  328.— VV.  Kuhne, 
Monatsb.  der  Kon.  Akad.  der  Wissensch.  zu  Berlin,  1859,  p.  400  :  Zeitsch.  f.  Biol.,  Bd. 
XXII,  p.  305  ;  Arch.  f.  Anat.  und  Physiol.,  1859. — Langley,  Journ.  of  I'hysicl.,  1899, 
vol.  XXIV. — Philipeaux  et  Vulptan,  Journ.  de  la  physiol.  de  Vhomnte  et  des  anim.  et 
C.  R.  Acad,  sc,  1863. — Rosenthal,  Centralbl.  f.  d.  med.  Wiss.,  1864,  p.  449. — Thier- 
NESSE  et  Gluc;e,  Bullet.  Acad.  roy.  Belgiqtie,  t.  VII,  Xo.  7. — Vulpi.\n,  C.  R.  Acad,  sc,  1873, 
t.  LXXVf,  p.  146  ;  Arch,  physiol.,  1876,  p.  597  ;  Leyons  sur  la  physiol.  gen.  et  com- 
paree  du  syst.  nerveux. 

Direction  of  the  transmission  :  part  played  by  the  dendrites. — Mislawskv,  Biol., 
1895,  p.  489. 

Rate  of  transmission  of  the  impulses. — Bernstein,  Centrabl.  f.  d.  med.  ]Viss.  1866; 
Arch.,  ftd.  ges.  Physiol.,  1868;  Unters.  und  d.  Erregimgsvorgang  in  Xerven  u.  IMuskeln. 
1891. — Du  Bois-Reymond,  Jahresb.  d.  phys.  Ges.  zu  Berlin,  II,  1845. — Chauveau, 
C.  R.  Acad,  sc,  t.  LXXXVIl,  1878,  pp.  95,  138,  238.— Grigorescu,  Biol,  1891  ;  Biol, 


THE  NERVOUS  ELEMENT  71 

1892,  p.  634  ;  Arch,  phijsiol.,  1894  ;  Helmholtz,  Monatsb.  d.  Berl.  Acad.,  1850,  1854  ; 
Arch.  /.  Ancit.  und  Phys.,  1850,  1852. — Helmholtz  et  Baxt  (mesure  chez  rhomme), 
Monatsb.  d.  Berl.  Acad.,  1867,  1870.— Hermann,  Handbuch,  2  vol.,  1  partie.— Mabey, 
Gaz.  Died.,  Paris,  1866  ;  Du  mouvem.  dans  les  fonctions  de  la  vie,  Paris,  1868. — H.  Munk,. 
Arch.f.  Anat.  und  FhysioL,  I860.— Place,  Arch.  v.  Pfluger,  1870,  t.  Ill,  p.  424.— Re- 
GNARD,  Influence  des  hautes  pressions,  Biol.,  1887,  p.  406. — Valentin,  Molesch.  Uniers., 
X,  1898.— WuNDT,  Arch.  f.  d.  ges.  Physiol.,  1870;  Unters.  z.  Median,  d.  Nerv.  und 
Musk.,  II,  Stuttgart,  1876.' 

Rate  ;  sensory  nerves. — Block,  Arch.  d.  physiol.  sc.  exp.,  1875,  p.  588. — HiRSCH, 
Molesch.  Unters.,  IX,  p.  183. — De  Jaager,  Arch.  /.  Anat.  und  Phys.,  1868,  p.  657. — 
KoHLRATJSCH,  Zcitsch.  f.  rat.  Med.,  XXVIII,  1866,  et  XXXI,  1868.— Schelske,  Arch.  f. 
Anat.  und  Phys.,  1864,  p.  151. — V.  Wittich,  Zcitsch.  f.  rat.  Med.,  XXXI,  1868,  p.  87. 

Electricity  (Ouvrages  generaux  a  consulter). — Bordieb,  Precis  d'electrotherapie, 
Paris,  J.-B.  Bailliere,  et  tils  ;  Precis  de  pliysique  biologique  (Collection  Testut),  Paris, 
O.  Doin. — Broca,  Art.  "  Electricite,"  I>ic<ion.  c?e  physiol.  de  Richet. — Jovbert,  Traite 
elementaire  d'electricite. — O.  Lodge,  Les  theories  modernes  de  Felectricite,  traduit  de 
r anglais  par  ]Meylan,  Paris,  Gauthier-Villars  et  tils,  1891.— C.  :Maxwell,  Traito  elemen- 
taire d'electricite,  traduit  de  I'anglais  par  G.  Richard,  Paris,  Gauthier-Villars,  1884. — 
Poincare,  La  theorie  de  Maxwell  et  les  oscillations  hertziennes  (Collection  Scientia), 
Paris,  G.  Carre  et  C.  Naiid. 

Excitability  of  nerves. — D'Arson\"al,  Duree  apres  la  mort,  C.  R.  Acad,  sc,  t.  CXVI, 

1893,  p.  1530. — C.  Bernard,  OEuxTes  diverses.  Lemons  sur  le  syst.  nerveux.  — Brown- 
Sequard,  Arch,  physiol.,  1892. — Gotch,  Infl.  temper.,  Journ.  of  Phys.,  1896,  p.  247. — 
Howell,  Budgett  et  Leonard,  Journ.  of  Physiol.,  1894,  p.  298.— Stefani,  Arch, 
ital.  de  bioL,  1899,  t.  XXXII,  p.  439.— Tissot,  Persist,  apres  la  mort.  Arch,  de  physiol, 

1894,  p.  142.— TscHiRiEW,  Arch.  f.  Anat.  und  Phys.,  1877,  p.  489.— G.  Weiss,  Legere 
traction,  C.  P.  Acad,  sc,  1899,  t.  CXXVIII,  p.  452.— Zederbal-m,  Einfl.  d.  Dehnung, 
Arch.  f.  Anat.  und  Phys.,  1882,  p.  116. 

Excitability  and  conductivity. — Gat>,  Arch.  f.  Anat.  und  Phys.,  1887,  p.  363;  1888, 
p.  395,  et  1889,  p.  3.>0. — Pistrowski,  Arch.  f.  Anat.  und  Phys.,  1893,  p.  205. 

Excitation  of  nerves.— D'Arsonval,  C.  R.  Acad.  sc.  1881,  t.  XCIT,  p.  1520  :  1891. 
t.  CXII,  p.  625  ;  Arch,  de  physiol.,  1889,  p.  246,  et  1893,  p.  387.— Bernheim,  Arch.  v. 
Pfluger,  1874,  t.  VII.  p.  60.— Bordier,  Arch,  de  physiol,  1897,  p.  543.— Boudet  (de 
Paris),  Trav.  lab.  Marey. — Ciiarbonnel-Salle,  These  Fac.  sc.  Paris,  1881. — Dubois, 
Arch,  de  physiol,  1897,  p.  740. — Engelmann,  Beweg.  an  Nervenfas.  b.  Reizung  mib 
Induct,  schl..  Arch.  v.  Pfluger,  1872,  t.  V,  p.  31.— Hallsten,  Arch.  f.  Anat.  und  Phys. 
1881,  p.  90.— HooRWEG,  Arch,  de  physiol  1898,  p.  269.— Kries,  Arch.  f.Anat  und  Phys. 
1884,  p.  337.— Lewandowsky,  Arch.  f.  Anat.  und  Phys.,  1899,  p.  352.— Marchand, 
Excit.  des  centres.  Arch.  v.  Pfluger,  1878,  t.  XVII,  p.  511.— Oelh,  Arch,  ital  de  biol. 
1891,  1893.  1898.— Sestchenow,  Arch.  v.  Pfluger,  1872,  t.  V,  p.  114.— Tiegel,  Arch.  v. 
Pfliigcr,  1876,  t.  XIII,  p.  598.— Wedenskt,  Arch,  de  physiol,  1891,  p.  687.— G.  Weiss, 
C.  R.  Acad,  sc,  1897  ;    Biol,  et  Congres  de  physiol.  de  Turin,  1901. 

Interferences. — Charpentier,  C.  R.  Acad.  sc.  et  Arch,  de  physiol. — Patrizzi,  Arch. 
ital  de  biol,  1896,  t.  XXV,  p.  1.— Valentin,  Arch.  v.  Pfluger,  t.  XIII,  1876,  p.  320.— 
Wedenskv,  C.  R.  Acad,  .sc,  1893,  t.  CXVII,  p.  240. 

Chemical  excitants.— E.-W.  Groves,  Jojirn.  of  Physiol,  1893,  p.  221.— Stefani,  Arch, 
ital  de  biol,  1805,  t.  XXII,  p.  183. — Sven  Akerlund,  Arch.  f.  Anal  und  Phys.,  1891, 
p.  279. — Wertiikimer,  Arch,  de  physiol,  1890,  p.  790. 

Polar  action  :  unipolar  excitation. — A.  Charpentier,  C.  R.  Acad,  sc,  1893  et  1899  ; 
Arch,  de  physiol,  1893,  a  1S99.— Chauveau,  Effets  physiol.  electric.  J. Anat.  et  Phys., 
de  B.S.,  1859  ;  L'tilisation  de  la  tension  electroscopique,  Soc  avanc  sc,  Lyon,  1874: 
Excitation  unipolaire,  C.  R.  Acad,  sc,  1875-1876. — Coxtrtade,  Arch,  physiol,  1890, 
p.  579. — Engesser,  Arch.  v.  Pfluger,  1875,  t.  X.  p.  147.— Leduc,  C.  R.  Acad,  sc,  1900, 
t.  CXXX,  p.  524  et  730.— Magini,  Arch,  ital  de  biol,  1883,  t.  IV,  p.  278.-0.  Nasse, 
Arch.  V.  Pfliigcr,  1870,  t.  Ill,  p.  476.— H.  Sewall,  Journ.  of  Physiol,  1880,  2,  vol.  Ill, 
p.  175. 

Sinusoidal  voltaisation. — D'Arsonval,  Arch,  de  physiol,  1893,  p.  387. 

Currents  of  high  frequency. — D"Arsonval,  Arch,  de  physiol,  1893,  p.  401. — Bordier 
et  Lecomte,  C.  R.  Acad,  sc,  1901. — Radzikowski,  Trav.  lab.  Instil  Solvay,  t.  Ill, 
fasc.  I. 

Magnetic  field  :  waves,  electric  rays. — Danilewski,  Arch,  de  physiol,  1897. — Rad- 
zikowski. Trar.  lab.  Instit.  Solvay,  t.  Ill,  fasc.  I. 

Latent  stimulation.— Bernstein,  Arch.  f.  Anat.  und  Phys.,  1882,  p.  329.— Boruttau, 
Arch.  f.  Anat.  und  Phys.,  1892,  p.  454. — Johan.  Gad,  Arch.  f.  Anal  und  Phys.,  1886, 
p.  263. — Mendelsohn,  Arch,  de  physiol.  1880,  p.  193. 

Local  excitability  of  the  different  portions  of  the  nerve. — A.  Beck,  Arch.  f.  Anat.  und 
Phys.,  1897,  p.  415,  et  1898,  p.  281. — I>ni.  Munk  et  P.  Schultz,  Arch.  f.  Anat.  und 
Phys.,  1898,  p.  297. 


72  ELEMENTARY  NERVOUS  FUNCTIONS 

Repeated  excitations  ;  physiological  tetanus. — Ch.  Bohr,  Arch.  f.  Anat.  und  Phys., 
1882,  p.  233. — Cyon,  Electrotherapie. — Duchenne,  Eleotrisatioii  localisee. — Grun- 
HAGEN,  Arch.  V.  Pfliiger,  1872,  t.  VI,  p.  157. — Kohnstamm,  Arch.  f.  Anat.  und  Phys., 
1893,  p.  125. — Kkies  und  Sewall,  Arch,  und  Phys.,  1881,  p.  66. — Kronecker  und 
NicoLAiDES,  Arch.  f.  Anat.  und  Phys.,  1883,  p.  27. — Kronecker  und  Stirling, 
Arch.  f.  Anat.  und  Phys.,  1878. — Von  Frey,  Arch.  f.  Anat.  und  Phys.,  1883, 
p.  43. — Fried.  Martius,  Arch,  f.  Anat.  und  Phys.,  1883,  p.  542. — Schoenlein, 
Arch.  f.  Anat.  und  Phys.,  1882,  p.  357  at  p.  369. — Valentin,  Arch.  v.  Pfliiger, 
1875,  t.  XI,  p.  481. 


CHAPTER    II 

NERVE     ENERGIES 

The  study  of  the  muscle  serves  as  model  for  that  of  the  nerve  ;  but 
this  latter  study  is  incomparably  less  advanced,  which  is  due  to  special 
conditions  affecting  experimentation  on  the  nerve,  these  being  less 
favourable  than  in  the  case  of  the  muscle. 

A.     ENERGIES   WHICH    ARE    DETECTABLE    IN    THE    NERVE  :    ORIGIN 

AND    SUCCESSION 

In  the  muscle,  energy  in  its  initial  condition  is  of  chemical  nature  ; 
in  its  final  state,  it  appears  as  heat  and  as  mechanical  work  ;  its  inter- 
mediate transformations  elude  our  observation  ;  we  know,  however, 
that  certain  electro  motor  phenomena  are  connected  with  the  produc- 
tion of  this  work.  In  the  nerve,  we  must  suppose  that  a  cycle  of  the 
same  nature  exists  ;  but,  far  from  being  able  to  indicate  precisely  the 
different  conditions  of  the  transformation  of  energy,  we  can  merely 
vaguely  point  them  out. 

Initial  condition. — In  the  nerve,  tlie  initial  energy  should  also  be  chemical  ;  as 
a  proof  of  this  may  be  cited  the  faculty  which  the  nerve  possesses  (as  does  every 
tissue)  of  breathing,  that  is  to  say,  of  burning  up  something  in  taking  up  oxygen 
from  the  blood  and  in  returning  to  the  latter  carbonic  acid  ; — the  final  and  the 
intermediate  energies  are  far  less  accurately  known  ;  however,  to  the  nerve 
must  be  ascribed  electromotor  phenomena  analogous  to  those  of  the  muscle. 

Final  condition. — Chauveau  teaches  that  nervous  energy  should  be  capable 
of  entire  reappearance  in  the  form  of  heat,  almost  as  in  the  case  of  the  muscle, 
which  contracts  in  vacuo,  when  no  mechanical  work  is  produced.  According  to 
him,  this  heat,  arising  at  the  point  of  termination  of  the  nerves  within  the  muscle, 
is  added  to  that  of  the  muscle,  and  may  even  increase  it  to  such  a  degree  that  it 
may  be  appreciable  by  the  thermometer. 

Yet  this  final  state  of  all  nervous  energy  is  not  that  which  occupies  our  atten- 
tion when  we  desire  to  express  the  special  impulse  wliich  the  nerve  brings  to 
bear  on  the  muscle  (or  anj^  organ  external  to  the  latter)  in  order  to  overcome  its 
molecular  equilibrium  and  to  cause  it  to  expend  its  own  individual  energy.  It 
is  scarcely  admissible  that  this  shock  is  the  result  of  calorific  vibrations.  Prob- 
ably in  this  case,  as  in  that  of  the  majority  of  organs,  heat  merely  follows  or 
accompanies  molecular  work  of  a  special  nature  which  is  accomplished  by  the 
motor  nerve  terminations  in  the  muscle,  in  order  to  arouse  in  the  latter  an 
excitable  condition. 

73 


74  ELEMENTARY  NERVOUS  FUNCTIONS 

It  has  been  asked,  without  it  being  possible  to  give  an  answer,  if  this  work  is 
of  an  electrical  nature.  This  idea  has  been  suggested  by  the  analogj'  which  has 
been  remarked  between  the  nerve  and  certain  electrical  apparatus,  and  also  by 
the  fact  that,  amongst  the  artificial  stimvili  of  the  muscle  and  of  the  tissues,  elec- 
tricity is  the  best  known.  But  these  are  rough  analogies  whose  insufficiency  is 
obvious.  An  opinion  on  this  subject  can  only  be  based  on  direct  and  convincing 
experiment.  Unfortunately,  we  have  no  means  of  isolating  the  nerve  termina- 
tions in  order  to  collect  directly  from  them  the  energies  which  they  give  off,  and 
to  determine  how  these  latter  affect  the  apparatus  ordinarily  used  in  physics. 

Transmitted  and  localized  energies. — The  initial  and  final  conditions  of  energy 
in  the  nerve  may  be  regarded  in  two  different  ways.  They  may,  fcu^  example, 
point  out  as  regards  the  first  the  form  assumed  by  the  energy  at  its  entrance 
into  the  receptive  pole  of  the  nevu"on,  and  as  concerns  the  second,  that  at  its  exit 
from  the  ramified  extremities  of  the  distributing  pole  :  thus  the  process  of  nerve 
conduction  is  carried  out.  They  may  also  express — and  this  is  their  most 
general  sense — the  successive  forms  of  energy  in  each  section,  or  at  each  point, 
of  the  isolated  nerve. 

Source  of  energy  and  excitation. — Whatever  idea  indeed  may  be  formed  of  the 
process  of  conduction  or  of  the  circulation  of  energy  in  the  direction  of  the  length 
of  the  fibres,  it  is  necessary  to  admit  that,  at  each  point  of  the  nerve,  a  local  cir- 
culation of  energy  exists  from  the  interior  to  the  exterior,  for  this  is  proved  by 
the  exchanges  with  the  blood  at  the  point  of  contact  with  the  capillaries  which 
accompany  the  nerve  throughout  its  length.  It  may  indeed  be  said  that,  just 
as  in  the  case  of  the  muscle,  this  is  the  source  from  which  energy  is  supplied,  and 
that  the  latter  does  not  take  its  rise  in  the  centres  or  in  the  organs  of  special 
sense.  As  in  the  case  of  the  muscle  also,  the  source,  properly  so  called,  of  enei'gj' 
which  lies  in  the  vessels  must  be  distinguished  from  the  source  of  the  stimulation 
which  comes  to  it  from  other  nerves  or  from  the  surrounding  medium  by  the 
intermediation  of  differentiated  peripheral  organs.  The  difference  between  it 
and  the  muscle  consists  in  the  fact  that,  in  the  latter,  the  expenditure  of  energy 
being  the  end  of  function,  this  energy  circulates  in  it  in  a  relatively  enormous 
quantity  ;  while  in  the  nerve,  conduction  and  excitation  being  the  end  of  func- 
tion, the  cvirrent  in  it  is  infinitely  weaker,  whence  the  difficulty  of  estimating  it, 
or  even  of  proving  its  presence. 

Reserve  of  energy. — Yet,  further,  as  in  the  muscle,  this  energy  is  not  abstracted 
from  the  blood  by  the  nerve  immediately,  at  each  moment  of  its  functional 
activity,  but  is  stored  up  in  its  tissue,  in  the  forni  of  an  alimentary  intracellular 
reserve,  which  is  expended  (probablj^  by  combustion)  in  proportion  to  its  activity. 
In  this  way  it  is  possible  to  explain  how  it  is  that  this  activity  may  persist  in  the 
nerve  for  sometime  after  all  its  connexions  in  the  vascular  system  have  been 
destroyed,  and  how  it  is  that  this  activity  definitely  ceases  when  this  isolation 
has  lasted  for  too  long  a  time.  Of  the  nature  of  the  substance  representing  the 
stored-up  energy  nothing  is  known  ;  it  may  be,  under  its  form  of  a  mobile  and 
immediately  utilizable  reserve,  a  hydrocarbon,  as  in  the  case  of  the  muscle,  and, 
in  its  dormant  form,  one  of  the  fats  which  surround  the  axon. 

ExjDeriment  teaches  us  further  that  the  reserve  of  energy  in  the  nerve,  which 
is  immediately  available,  forms  but  a  small  portion  of  its  total  reserve.  Each 
single  stimulation  gives  rise  in  the  nerve  (and  by  rebound  in  the  muscle)  to  a 
very  limited  expenditure  of  its  total  potential  energy.  The  reconstitution  of 
the  portion  expended  is  effected  so  rapidly  that  it  seems  to  be  an  opposite  and 
necessary  phase  of  this  expenditure,  so  long  as  the  provision  is  not  exhausted. 
When  the  nerve  is  separated  from  its  vessels,  this  exhaustion  is  fatal  ;  when  the 
nerve  maintains  its  vascular  connexions  this  exhaustion  is  very  difficult  to 
obtain,  whence  arises  the  somewhat  exaggerated  but  relatively  true  notion, 
that  the  nerve  is  incapable  of  fatigue. 


NERVE  ENERGIES  75 

This  limitation  in  the  expenditiu-e  agrees  with  another  experimental  fact, 
namely,  that  the  activity  of  the  nerve,  like  that  of  the  muscle,  can  only  be  main- 
tained by  an  incessant  renewal  of  the  excitation  in  it.  Since  Weber,  every  time 
that  we  see  a  muscle  in  a  state  of  tonic,  that  is  to  say,  continuous  contraction, 
we  regard  it  as  receiving  from  its  motor  nerve  successive  closely  approximated 
but  discontinuous  impulsions,  while  at  the  same  time  the  nerve  receives  them 
in  the  same  order  from  the  apparatus  which  excites  it.  We  know  indeed  that 
the  only  correct  way  of  obtaining  this  prolonged  tension  of  the  muscle  is  to 
supply  it  with  impulsions  of  this  order,  and  the  employment  of  the  interrupter 
(trembleur)  of  du  Bois-Reymond  corresponds  to  this  necessity. 

To  return  to  the  energies  which  can  be  detected  in  the  nerve.  There  are  two 
which  have  been  particularly  studied  and  established  in  it  :   heat  and  electricity. 

Heat  developed  by  the  nerve. — The  amount  of  heat  given  off  by  the 
nerve  tissue  is  extremely  small.  In  isolated  nerve  trunks  it  eludes 
observation,  as  is  shown  by  the  experiments  of  Rolleston,  Stewart  and 
of  Boeck,  who  have  endeavoured  to  estimate  it  without  result,  using 
apparatus  (bolometres)  sensitive  up  to  -,/,,,,  of  a  degree.  In  the 
brain,  Mosso,  by  producing  asphyxia,  has  caused  obvious  heat  produc- 
tion, w^hich  may  be  fairly  attributed  to  a  local  process,  but  without 
producing  the  complication  of  displacement  of  heat  brought  from 
another  part  by  the  circulation  (see  Animal  Heat,  pages  389-396). 
Chauveau  considers,  for  his  part,  that  a  small  fraction  of  the  heat 
evolved  by  muscle,  during  its  stimulation,  may  be  due  to  the  nerve 
terminations.  To  this  is  limited  our  knowledge  concerning  the  heat 
given  off  by  the  nervous  system. 

Electricity  developed  in  the  nerve  has  been  the  subject  of  a  very 
large  number  of  researches  and  observations,  and  hence  merits  a 
separate  study. 

B.     ELECTRIC    ENERGY    OF    NERVE 

The  nerve  is  the  seat  of  electromotive  forces  which  are  fairly  easy  to 
investigate.  But  their  study  necessitates  a  mutilation  of  the  organ 
examined,  and  thus  much  complicates  the  conditions  of  the  experi- 
ment and  the  explanations  which  are  given  of  it. 

1.  Current  of  repose. —  As  has  been  remarked  above,  no  means 
exists  by  which  the  neurons  can  be  isolated,  in  the  sense  of 
detaching  them  from  their  connexions  at  either  extremity  and  of  observ- 
ing what  passes  at  each  of  these  extremities.  We  are  compelled  to 
experiment  on  fragments  taken  from  the  continuity  of  the  nerves. 

Experiment. — Let  a  segment  of  nerve  isolated  by  two  sections  be  taken  ;  this 
small  nervous  cylinder  will  be  seen  to  present  at  its  surface  an  altogether  special 
distribution  of  the  electrical  potential.     Starting  from  the  middle  zone,  which  is 


76  ELEMENTARY  NERVOUS  FUNCTIONS 

known  as  its  equator,  this  potential  is  observed  to  gradually  fall,  in  proportion  as 
the  two  extremities  are  approached.  Between  the  equator  and  each  of  the  extremi- 
ties, this  difference  is  at  its  maximum  ;  between  points  which  are  more  nearly 
approximated,  it  is  less  in  proportion  as  the  distance  itself  is  less.  Between  the 
two  extremities,  as  between  all  points  symmetrically  situated  as  regards  the 
equator,  it  is  nil. 

If  this  segment  of  nerve  be  cut  in  two,  each  one  of  the  two  halves  presents 
individually  the  same  distribution  of  potential.  The  case  is  obviously  analogous 
to  that  of  a  magnet  which  is  broken  in  pieces,  and  of  which  each  fragment  is 
furnished  with  two  poles,  just  as  the  primitive  magnet  of  which  it  forms  a  por- 
tion ;  but  with  this  difference,  that  the  detached  fragments  of  the  nerve  are  not 
furnished  with  opposite  poles  at  their  extremities,  but  the  two  poles  of  the  same 
nature  are  electrically  oi:)posed  to  their  equator.  So  far  as  it  is  possible  to  carry 
this  analysis,  this  arrangement  and  distribution  of  the  potential  will  be  found 
to  be  present  and  symmetrically  repeated  as  concerns  the  two  lialves  of  all  the 
fragments.  A  fragment  of  nerve  fibre  will  be  found  to  behave  in  the  same  manner. 
It  is  possible  that  the  component  particles  of  the  fibre,  inasmuch  as  these  particles 
represent  the  elementary  organization  of  the  nervous  protoplasm,  would  present 
the  same  phenomenon.  The  reasoning,  indeed,  is  applicable  both  to  the  nerve 
and  to  the  magnet  ;  analysis  in  both  cases  proves  that  the  distribution  of  the 
polarities  is  connected  with  the  molecular  structure,  or  with  the  component 
particles,  these  being  of  extreme  tenuity. 

Intensity. — When  an  attempt  is  made  to  estimate  the  intensity  of  the  current 
of  repose,  that  which  is  determined  is  the  intensity  of  the  derivation  received 
in  tlie  galvanometer.  The  intensity  of  the  derivation  is  about  0-02  Daniel  (or 
about  0"02  volts).  It  varies  little  between  different  animals,  equally  little  betiveen 
different  nerves,  whether  motor,  sensory,  or  mixed  ;  but  it  is  stronger  in  the  non- 
myelinated nerves  than  in  those  provided  with  myelin  (Kuhne  and  Steiner). 
Frederic  has  ascertained  it  to  be  0-048  (Daniel)  in  the  lobster. 

Origin  of  the  electric  currents  of  nerve. — To  what  must  the  currents  which 
are  thus  observed  in  nerves  be  attributed  ?  Are  they  the  result  of  a  iuerely  local 
reaction  of  tlie  metallic  electrodes  on  the  nervous  tissue  ?  No,  because  they 
are  equally  well,  or  even  better  observed  when  inactive  and  non-polar izable  elec- 
trodes are  made  use  of  to  collect  them.  The  differences  of  potential  which  give 
rise  to  them  must  then  pre-exist  in  the  separated  nerve  segment,  and  this  apart 
from  any  contact  of  the  conductors  by  which  they  are  carried  to  circulate  in  the 
galvanometer.  The  nerve  segment,  or  rather,  the  particles  which  compose  it, 
seem  at  the  first  glance  to  resemble  open  cells,  in  which  the  cui'rent  only  circulates 
when  tlieir  polar  wires  are  united. 

Derived  currents. — This  hypothesis  may  be  brovight  forward  ;  but  it  may  also 
be  asserted,  and  with  more  probability,  tliat  these  particles  (like  those  of  the 
magnet)  are  the  seats  of  currents  completed  in  themselves  (much  more  compli- 
cated, it  is  true,  than  those  of  the  magnet).  When  the  nerve  segment  is  con- 
nected with  the  galvanometer  by  two  points  on  its  surface  which  are  unsym- 
metrically  situated,  there  arises  merely  a  derivation  of  these  particular  currents, 
similar  to  that  which  occurs  in  a  batterj-  circuit  when  two  of  the  points  of  its 
interpolar  wire  are  united  by  a  second  closed  wire  wliicli  passes  tlirough  a  gal- 
vanometer. 

Do  nerve  currents  pre-exist  ? — We  have  just  seen  that  they  pre-exist  as  regards 
the  ai^plication  of  electrodes,  but  do  thej'  exist  anterior  to  the  mutilation  of  the 
nerve  which  is  affected  in  order  that  the  segment  to  be  examined  may  be  removed? 
In  other  words,  will  an  isolated  neuron,  not  broken  by  the  cutting  instrument, 
present  them  ?  This  question  is  still  under  discussion  ;  nevertheless,  many 
physiologists  think,  with  Hermann,  that  the  answer  is  in  the  negative.  Du  Bois- 
Beymond  regarded  the  currents  thus  observed  in  the  nerve,  apart  from  any  func- 


NERVE  ENERGIES  77 

tional  activity,  as  being  currents  of  repose  ;  Hermann  describes  them  as  currents 
of  alteration. 

Current  of  alteration. — Section  of  tlie  nerve  trunk  by  the  cutting  instrmuent 
does  not  merely  separate  the  component  particles  of  the  fibres  of  this  nerve  ;  it 
necessarily  destroys  the  structure  of  these  fibres  to  a  certain  extent,  mixes  the 
separated  substances,  which  hence  react  amongst  themselves,  without  taking 
account  of  the  fact  that  the  air  penetrates  and  probably  takes  part  in  these  reac- 
tions. Hence  the  origin  of  currents  of  chemical  source,  but  which  arise  under 
caitirely  artificial  conditions.  They  wovild  not  have  much  interest  for  us  if  they 
were  not  themselves  the  image  of  converse  cirrrents,  more  feeble,  indeed,  but 
otherwise  altogether  similar,  which  are  connected  with  the  functional  activity 
of  the  nerve  at  the  instant  of  stimulation.  But  these  last  are  not  observed  with- 
out the  complication  arising  from  the  presence  of  the  first. 

Transverse  longitudinal  current  ;  axial  current.  —  In  the  case  of  a  detached 
segment  of  nerve,  the  gi-eatest  difference  of  i:)otential  is  observed  between  its 
equator  and  one  or  other  of  its  cut  extremities.  This  is  obvious  when  the  equator, 
as  also  one  of  the  two  extremities  (by  non-polarizable  electrodes)  is  connected 
with  the  galvanometer.  But  between  the  two  extremities  the  potential  value  is 
not  equal  ;  if,  indeed,  the  two  ends  of  the  nerve  segment  are  connected  with  the 
galvanometer,  the  existence  of  a  much  feebler  current,  which  Mendelssohn  has 
observed,  and  called  the  axial  current,  becomes  obvious  in  opposition  to  the  pre- 
ceding cvu-rent,  which  is  the  transverse  longitudinal  ciu-rent  ;  its  intensity  is  about 
ten  times  less  than  that  of  this  latter.  The  interest  of  the  axial  current  arises 
from  the  fact  that  it  has  a  definite  orientation  with  regard  to  the  phj'siological 
conduction  of  the  nerve  under  examination.  As  regards  this  latter  conduction,  it 
has  an  opposite  direction  ;  it  is  ascending  in  the  posterior  roots  (centripetal) 
and  descending  in  the  anterior  roots  (centrifugal).  Is  this  orientation  of  the 
axial  current  connected  with  the  mechanism  of  the  phenomena  of  conduction, 
or  rather  is  it  allied  to  a  phenomenon  of  a  trophic  nature,  of  alteration,  which 
would  be  unecjual  in  the  two  ends,  according  to  the  respective  locality  they 
occupy  in  the  intact  nerve  with  regard  to  the  cell  ?  This  is  not  precisely 
known.  Like  the  transver.se  longitudinal  ciu-rent,  the  axial  cui'rent  undergoes 
a  modification  of  its  intensity  (negative  variation)  tlirough  the  fact  of  the 
activity  of  the  nerve,  when  the  latter  is  stimvdated. 

2.  Negative  variation  ;  current  of  action.  —  Let  a  nerve  segment  be 
prepared  in  such  a  way  that  two  unsymmetrical  points  are  connected 


Fig.   37. — Diagram   of   an   experiment   for   the   determination   and   estimation   of   the 

negative  variation. 

EE',  DD',  living  nerve.  In  EE'  excitation.  In  DD'  derivation  of  the  longitudino-transverse 
current,  called  that  of  repose  or  alteration,  whose  direction  is  indicated  by  the  largest  of  the  two 
arrows.  At  the  moment  of  excitation,  contrary  current  of  less  intensity  wliich  declares  itself  as  a 
negative  variation  of  the  longitudino-transverse  current. 


78 


ELEMENTARY  NERVOUS  FUNCTIONS 


with  the  termmals  of  the  galvanometer.  The  needle  of  the  latter 
deviates  in  a  certain  direction  to  a  certain  extent  which  is  recorded. 
The  other  extremity  of  this  nerve  is  stimulated  ;  the  needle  returns 
towards  zero,  but  without  attaining  this  point,  thus  indicating  either 
a  diminution  of  the  intensity  of  the  so-called  current  of  repose,  giving 
rise  to  what  is  known  as  the  negative  variation  (du  Bois-Reymond)  ; 
or  an  inverse  current  of  less  intensity  than  the  current  of  alteration, 
and  which,  on  this  hypothesis,  is  known  as  the  current  of  action. 

Its  importance. — Whatever  explanation  may  be  given  of  it,  this 
phenomenon  is  a  very  important  one,  because  it  is  obviously  allied 
to  the  active  condition  of  nerves  ;  this  may  be  inferred  from  the  follow- 
ing observations  : — 


K 

iilljiiiiiii 

\ 

i 

lil 

Fig.   38. — Cm-rents  of  the  optic  nerve  and  of  the  retina. 

Above,  diagram  of  the  arrangement  of  the  experiment.  Below,  graphic  expression  of  the 
modifications  of  these  currents  during  repose  (darkness)  and  activity  (ihumination). 

The  darkness  is  marked  by  hatching. 

On  the  left,  current  of  alteration  of  the  optic  nerve.  The  surface  of  section  is  negative  with 
regard  to  the  longitvadinal  surface.  During  illumination,  this  negative  condition  is  diminished. 
When  the  illumination  ceases  it  also  diminishes  slightly  ;  then  the  cvirrent  returns  to  its  initial 
value  (Kulme  and  Steiner). 

On  the  right,  retinal  current.  The  surface  of  the  rods  is  negative  with  regard  to  that  of  the 
fibres.  During  illumination,  this  negative  condition  is  at  first  increased,  it  then  becomes  less 
marked  (sometimes  diminished).  On  the  interruption  of  the  illumination,  fresh  augmentation  ; 
then  return  to  the  initial  condition  (Kulmer  and  Steiner). 


(a)  The  magnitude  of  the  negative  variation  is  definitely  related  to 
that  of  the  stimulation,  just  as  is  the  magnitude  of  the  muscular  con- 
traction. A.  Waller  has  verified  this  point  as  concerns  segments  of 
detached  nerves  experimented  upon  in  the  moist  chamber.  He  has 
noticed,  it  is  true,  that,  when  the  intensity  of  the  stimulation  exceeds 
that  which,  in  the  case  of  a  nerve  in  situ,  would  give  rise  to  maximum 
contractions,  the  magnitude  of  the  negative  variation  is  still  capable 


NERVE  ENERGIES 


-9 


of  increase.  The  negative  variation  being  the  special  response  of  the 
nerve  to  stimulation,  and  contraction  that  of  the  muscle  to  stimulation 
transmitted  by  the  nerve,  there  is  no  reason  Avhy  the  limits  of  sensation 
should  be  the  same  in  the  two  organs.  But  the  parallel  progression  of 
the  two  reactions  demonstrates  their 
union  in  nervo-muscular  function. 

(b)  Its  time  of  propagation  (interval 
of  time  which  separates  it  from  the 
stimulation)  is  definitely  connected 
ivith  the  length  of  the  course  which  it 
runs,  and  it  is  the  same  as  for  the 
muscular  contraction.  We  may  thus 
substitute  the  negative  variation  for 
the  muscular  contraction  as  evidence 
of  nervous  activity.     As  regards  the   ^m.  39.-Actiono£ancestlietic.(ehluro- 

form)  on  the  internal  activity  of 
the  nerve  (negative  variation),  after 
Waller. 

On  the  left,  series  of  negative  variations 
obtained  by  stimulating  the  nerve  not  sub- 
mitted to  anaesthetic  vapours.  On  the 
right,  absence  of  the  negative  variations 
during  anaesthesia.  The  current  of  repose 
at  this  moment  presents  slow  variations  in 
its  intensitv. 


superficial  or  deep  nerves,  which 
have  no  direct  connexion  with  the 
muscles,  it  may  serve  as  a  means  of 
research  and  of  control  in  the  study 
of  their  special  functions. 

(c)  The  negative  variation  is  in- 
dependent of  the  nature  of  the  exci- 
tation made  use  of.  It  may  be  elicited  by  stimuli  other  than  electricity, 
and  more  especially  by  the  physiological  excitant,  in  other  words,  the 
normal  excitant  of  the  nerve  itself.  Holmgren,  Kuhne  and  Steiner 
have  demonstrated  it  in  the  optic  nerve  and  in  the  retina,  by  sub- 
jecting the  latter  to  its  specific  excitant — light.  Beauregard  and 
Dupuy  have  observed  it  in  the  acoustic  nerve,  by  stimulating  the 
internal  ear  by  the  sonorous  waves.  Du  Bois-Reymond  had  already 
noticed  that  it  may  be  elicited  in  the  motor  nerve,  by  stimulating  the 
latter  in  a  reflex  manner  by  means  of  a  sensory  nerve.  It  may  also 
be  elicited  by  the  excitation  of  the  cerebral  motor  area. 

(d)  The  negative  variation  is  no  longer  produced  ivhen  the  nerve  is  sub- 
jected to  the  action  of  anaesthetics  (Waller).  In  every  way,  then,  it  is 
closely  connected  with  the  activity  of  the  nerve,  and  may  be  taken  as 
■evidence  and  measure  of  this  activity. 


Wave  of  excitation  or  of  propagation  of  excitation. — From  wliat  has  just  been 
said,  it  naay  be  inferred  that  the  negative  variation  is  connected,  in  each  section 
of  the  nerve,  with  the  excitation  of  this  section  during  the  passage  of  the  latter. 
In  other  words,  it  is  connected  with  what  is  commonly  called  the  icave  of  excita- 
tion ;  assiu-edly  a  very  complex  phenomenon,  in  which,  as  has  been  seen,  elec- 
-.tricity  takes  a  part,  but  which  we  have  no  right,  nor  even  any  plausible  reason. 


80  ELEMENTARY  NERVOUS  FUNCTIONS 

to  call  an  electi-ic  wave,  that  is  to  say,  one  similar  to  those  which  pass  through 
the  wires  of  the  telegraph,  or  which  are  transmitted  through  dielectrics. 

If,  following  the  example  of  the  majority,  we  neglect  the  current  of  alteration, 
which  is  wanting  in  normal  conditions,  we  shall  rejoresent  the  negative  variation 
as  a  ivave  of  negative  potential  (abbreviated  into  negative  tvave),  which  passes 
through  the  nerve  from  one  extremity  to  the  other.  As  a  potential  of  a  given 
denomination  cannot  exist  apart  from  a  jDotential  of  the  opjDosite  denomination, 
it  follows  that,  at  its  entry  into  the  nerve,  it  is  confined  to  a  positive  zone,  which 
is  in  front  of  it ;  at  its  exit  to  a  positive  zone  which  is  behind  it  ;  in  its  covirse  it 
is  comprised  between  two  positive  zones,  the  one  in  front,  the  other  behind  it. 

Diphasic  current. — In  passing  from  the  commencement  to  the  end  of  the  nerve, 
the  relationship  of  the  negative  and  positive  zone  is  inverted.  What  is  known 
as  the  current  of  action  acts  in  the  same  way.  Let  a  nerve  trunk  be  prepared 
whose  two  ends  are  connected  with  the  galvanometer  ;  if  an  impulse  passes 
through  it  from  one  end  to  the  other,  the  galvanometer  (if  sufficiently  mobile) 
will  undergo  two  oscillations,  the  one  opposed  to  the  other,  corresponding  to  the 
entrance  and  exit  of  the  impulse. 

The  diphasic  variation  of  the  currents  is  difficult  to  demonstrate  in  nerves, 
but  is  easily  observed  in  the  case  of  muscles,  especially  the  heart,  which  presents 
a  real  and  somewhat  slow  wave  of  proi3agation  of  the  impulse  through  its  fibres. 
The  electric  currents  of  nerve  and  of  muscle  are  siifficiently  similar  to  be  ex- 
pressed under  the  same  general  formula. 

Form  of  the  lines  of  flow  of  the  current  of  action  in  the  stimulated  point.— 
Considered  in  a  given  section  of  the  continuity  of  tlie  nerve  (in  the  middle  of  its 
length,  for  example),  the  negative  variation,  save  that  its  differences  of  potential 
are  weaker  and  its  polarities  inverted,  recalls  the  distribution  of  the  so-called 
current  of  repose  or  of  alteration  of  the  nerve  ;  it  is  capable  of  being  depicted 
in  a  similar  manner.  In  this  case  the  equator  is  of  a  higher  potential  than  the 
extremities.  As  to  the  cui-rent  of  repose,  it  may  be  asked  if  these  potentials 
correspond  to  opposed  non-satisfied  tensions,  or  rather  to  true  ciu-rents  circulating 
in  completed  circuits. 

The  latter  supposition  is  probably  correct.  These  circuits  may  be  depicted 
as  follows  :  on  the  stu'face  of  the  stimulated  nerve  (or  that  of  the  nerve  mole- 
c\iles),  their  lines  of  flux  proceed  to  meet  each  other,  but  without  actually  doing 
so,  in  a  direction  parallel  to  the  length  of  the  nerve  ;  having  arrived  at  the  nega- 
tive zone,  they  return,  follow  the  opposite  direction  in  the  depth  of  the  nerve 
and  complete  the  circuit.  In  this  way  these  currents  form  a  double  series  of 
rings  arranged  round  a  common  axis.  They  may  be  compared  to  two  tyres 
fixed  on  the  same  axis,  in  which  the  currents  circulate  in  opposite  directions. 
It  will  be  noticed  that  in  such  a  tyre  the  lines  of  force  circulate  only  in  the  interior. 

Displacement  of  the  phenomenon  with  the  propagation  of  the  impulse. — In 
projjortion  as  tlie  wave  progresses  in  the  nerve,  the  potential  is  inverted  in  the 
sections  which  follow  each  other.  Each  section,  taken  by  itself,  is  indeed  posi- 
tive when  the  impulse  approaches  it,  negative  when  the  latter  reaches  it,  once 
again  positive  when  it  leaves  it. 

We  know  the  rate  of  the  progression  of  this  wave,  but  we  are  ignorant  of  its 
length  ;  in  acting  in  the  manner  just  mentioned,  we  do  not  employ,  indeed,  any 
direct  or  indirect  means  which  are  really  accurate  in  order  to  ajipreciate  it.  We 
shall  demonstrate,  a  little  farther  on,  a  method  different  from  the  preceding, 
which  has  been  contrived  for  the  piu-pose  of  measuring  it. 

If  the  nerve  is  invaded  by  a  series  of  successive  impulses  very  closely  approxi- 
mated (such  as  induction  shocks),  it  will  evidently  be  traversed  by  a  series  of 
these  waves  which,  arriving  one  by  one  at  its  extremity,  will  give  rise  in  it  to  a 
series  of  variations  of  the  current  of  the  same  rhythm  as  themselves.  If  these 
variable  cvurrents  are  received  in  a  telephone  they  will  produce  a  sound  whose 


NERVE  ENERGIES  81 

pitch  indicates  their  number  in  a  given  time.  If  they  are  received  by  a  galvano- 
meter, the  needle,  owing  to  its  inertia,  will  not  return  to  its  initial  condition 
during  the  very  short  intervals  between  these  successive  variations,  and  will 
maintain  a  median  position  so  long  as  these  impulses  last. 

Intensity  of  the  current  of  action,  or  of  the  negative  variation. — As  for  the 
current  of  repose,  tliis  word  intensity  must  be  understood  in  a  purely  relative 
sense,  because  the  absolute  value  of  the  phenomenon  is  unknown.  And  for  this 
reason.  The  wires  of  the  galvanometer  being  arranged  on  a  section  of  nerve 
in  an  appropriate  manner,  at  the  instant  when  currents  arise  in  this  segment 
they  are  divided  into  two  portions  ;  the  one  (principal  current)  circulates  in  the 
nerve,  the  other  (derived  current)  circulates  in  the  galvanometer.  In  this  case 
there  is  no  means  of  ascertaining  the  connexion,  as  regards  magnitude,  which 
exists  between  the  principal  and  the  derived  current.  It  is  only  known  that 
the  direction  of  the  derived  current  is  the  same  as  tJuit  of  the  principal  current,  and 
that  its  intensity  is  proportional  to  it  ;  yet  this  is  very  valuable  information.  •  It 
is  possible  that  the  derived  current  is  but  a  very  small  fraction  of  the  internal 
current  of  the  nerve,  and  that  it  represents  merely  the  losses  of  the  latter,  which 
are  due  to  faulty  isolation,  losses  wliich  are,  however,  too  minute  to  alter  the  func- 
tional activity  of  the  nerve.  It  is  remarkable  that,  in  case  of  a  nerve  in  situ  and 
unnautilated,  only  a  very  weak  derivation  is  manifested  when  it  is  treated  in 
the  manner  which  lias  just  been  referred  to  ;  to  observe  the  negative  variation 
a  cut  nerve  must  be  operated  on,  just  as  if  the  section  had  the  effect  of  opening 
up  some  of  the  closed  cycles  in  which  the  currents  circulate. 

(a)  Intensity  in  relation  to  the  current  of  repose  or  of  alteration. — -Measured,  as 
has  just  been  observed,  by  the  derived  ciirrent  which  is  received  in  the  galvano- 
meter, the  intensity  of  the  negative  variation  is  much  feebler  than  that  of  the  so-called 
current  of  repose  or  of  alteration. — It  represents  in  the  frog  about  the  tenth  part 
of  it,  and  still  less  in  mammals.  Its  denomination  of  negative  variation  takes 
its  origin  from  the  fact  that  it  always  presents  itself  as  a  diminution  of  tliis 
current  of  repose.  Whether,  indeed,  the  current  of  repose  really  pre-exists,  or 
whether  it  arises  through  the  mutilation  of  the  nerve,  which  is  necessary  in  order 
that  the  internal  circuits  of  nerve  elements  may  be  made  manifest  by  our  galvano- 
meters, the  electrical  phenomenon  which  is  connected  with  the  activity  of  the 
nerve  during  its  stimulation  only  appears  to  us  as  a  converse  (but  unequal)  modi- 
fication of  this  ciirrent  which  we  cannot  avoid  vmder  the  ordinary  experimental 
conditions.  Other  things  being  equal,  the  negative  variation  will  be  the  greater 
in  proportion  as  the  current  of  repose  is  greater.  When  there  is  no  ciirrent  of 
repose,  there  is  no  negative  variation. 

(b)  Intensity  in  relation  to  the  magnitude  of  the  excitation. — As  has  been  said 
above,  the  intensity  of  the  negative  variation  is  definitely  related  to  the  intensity 
of  the  excitation.  It  increases  with  the  latter  up  to  a  maximum  which  is  not 
exceeded.  It  behaves  itself  in  this  regard  like  muscular  contraction  ;  it  has 
nearly  the  same  threshold  as  the  latter  ;    and  closely  follows  its  variations. 

Remark. — The  excitations  which  are  brought  to  bear  on  a  nerve  are  either 
simple  (isolated  closing  or  opening  of  the  circuit,  induction  shock,  static  dis- 
charge), or  composite  (due  to  the  repetition  of  a  certain  number  of  stimuli  in  a 
given  interval  of  time).  In  order  to  observe  negative  variation,  composite  ex- 
citations are  habitually  employed  (called  tetanizing).  The  reason  of  this  is  that 
in  order  to  overcoine  the  inertia  of  the  needle  of  the  galvanometer,  or  that  of  the 
mercvirial  colvmm  of  a  capillary  electroineter,  it  is  necessary  that  the  impulses 
which  arise  from  the  electric  current  be  repeated  a  certain  number  of  times. 
These  successive  impulses  fix  the  needle  in  the  median  position,  or  that  of  rela- 
tive immobility.  The  form  of  movement  of  a  galvanometric  needle  does  not  in 
this  case  reproduce  the  elementary  form  of  the  electrical  phenomena  under  obser- 

P  G 


82  ELEMENTARY  NERVOUS  FUNCTIONS 

vation,  nor  its  periods  ;  it  merely  shows  the  general  tenoiir  of  it.  When  the 
experiment  is  conducted,  no  longer  on  myelinated  nerves,  but  upon  non-myelin- 
ated  nerves,  in  which  the  current  of  repose  is  stronger  and  the  negative  variation 
greater,  the  simple  excitations  j)roduced  by  induction  shocks,  or  even  the  break- 
ing or  making  of  a  constant  current,  become  competent  to  produce  a  correspond- 
ing isolated  negative  variation.  In  these  conditions,  and  thanks  to  certain  con- 
trivances, into  the  details  of  which  we  cannot  enter  here,  it  is  possible  to  closely 
follow  the  general  form  of  the  electrical  modification  thus  produced. 

Form  of  the  negative  variation.  — This  form  closely  resembles  that  of  a  muscu- 
lar contraction.  Its  period  of  augmentation  is  abrupt  and  immediately  fol- 
lowed by  a  period  of  decline  which  is  much  longer. 

Positive  variation. — When  the  negative  variation  is  over,  it  is  followed  by  an 
inverse  variation  of  positive  direction,  which  is  more  or  less  marked,  and  which 
may  be  absent.  In  the  case  of  a  nerve  which  has  been  mutilated  in  order  to 
produce  the  derivation  proceeding  to  the  galvanometer,  before  any  stimulation 
there  may  be  observed  :  (1)  a  so-called  current  of  repose  ;  (2)  at  the  moment 
of  stimulation  a  negative  variation  of  this  current  of  repose  ;  (3)  a  positive 
variation  of  this  current  of  repose.  Some  authors  think,  with  Hering,  that  the 
positive  variation  is  connected  with  the  phenomena  of  nerve  restoration  after 
stimulation,  just  as  the  negative  variation  is  connected  with  the  waste  of  this 
nerve  during  its  excitation. 

Unipolar  methods  for  the  study  of  electrical  variations  of  the  nerve. — In  the 
preceding  experiments  the  excitations  supplied  to  the  nerve  are  bipolar,  and  the 
electrical  phenomenon  which  is  the  consequence  of  them  is  a  modification  of  its 
current  of  action  received  in  a  derived  circuit  which  passes  through  the  galvano- 
meter. In  other  words,  the  nerve,  in  two  localities  separated  the  one  from  the 
other,  is  intercalated  in  two  circuits,  the  one  intended  to  provide  the  current 
which  excites  it,  the  other  intended  to  receive  the  current  arising  in  it  as  the 
result  of  excitation.  But  the  nerve  may  be  also  stimulated  in  a  unipolar  fashion, 
in  a  single  point  of  its  progress  ;  and,  on  the  other  hand,  if  the  nerve  presents 
at  a  distance  a  variation  of  its  potential,  it  is  possible,  by  connecting  it  to  the 
earth  by  a  conductor  which  passes  through  a  galvanometer,  an  electrometer,  or 
a  galvanoscopic  paw,  to  act  in  a  unipolar  manner  on  these  different  rheoscopes, 
which  will  demonstrate,  each  one  in  its  special  way,  the  current  which  passes 
through  them  ;  the  two  first  will  undergo  a  deviation  which  will  be  of  a  different 
tenour  according  to  the  direction  of  the  current  (negative  or  positive),  the  last 
will  respond  by  a  muscular  contraction.  Precautions  shoixld  be  taken  to  prevent 
the  stimulating  current  directly  reaching  the  rheoscope,  which  is  intended  to 
demonstrate  the  ciirrent  which  takes  origin  in  the  stimulated  nerve.  By  this 
means,  therefore,  it  is  possible  to  render  evident  the  current  of  action  of  the  nerve 
without  mutilation  of  this  latter,  and  without  giving  rise  in  advance  to  a  current 
of  alteration.     This  is  maintained  by  Charpentier,  who  has  contrived  this  method. 

Oscillatory  variations  of  the  electric  potential  of  the  nerve  during  its  stimula- 
tion,— According  to  this  author,  the  nerve  thus  stimulated  is  traversed,  from  its 
point  of  excitation,  by  a  wave  which  has  obviously  the  same  rate  of  propagation 
as  the  negative  variation.  This  wave  is  accompanied  with  a  variation  of  the 
potential  and,  on  its  passage  to  the  point  at  which  the  nerve  is  connected  with 
the  rheoscope,  this  variation  is  made  perceptible  by  the  latter.  On  account  of 
its  very  slow  rate  of  progress,  this  wave  is  not  that  indeed  of  tlie  stimulating 
current,  but  a  physiological  wave,  in  which  electrical  phenomena,  amongst  many 
others,  take  part.  It  should  be  noted  that  the  stimulation  which  gives  rise  to 
it  is  not  necessarily  tetanizing,  but  may  consist  of  a  simple  excitation,  such  as 
that  which  arises  in  the  nerve  from  making  or  breaking  the  current.  So  far  the 
phenomenon  does  not  differ  from  that  with  which  we  are  already  acquainted, 


NERVE    ENERGIES  83 

except  as  regards  the  means  employed  to  render  it  evident.  The  new  fact  brought 
forward  by  Charpentier  consists  in  the  oscillatory  nature  of  the  variation  of  poten- 
tial which  takes  origin  at  the  point  stimulated,  and  is  thence  transmitted  along 
the  nerve.  A  simple  stimulation  (induction  shock,  making  of  current)  produces, 
according  to  this  author,  not  a  half-oscillation  like  that  which  is  known  as  nega- 
tive variation,  or  even  an  entire  oscillation,  but  a  series  of  oscillations,  which 
decrease  locally  while  they  are  transmitted  to  a  distance.  To  demonstrate  the 
oscillatory  nature  of  the  phenomena,  the  possibility  of  making  the  communica- 
tion of  the  conductor  with  the  electrometer  is  limited  to  determinate  and  succes- 
sively variable  periods  after  the  excitation  of  the  nerve.  It  is  then  seen  that  the 
deviation  of  the  instrument  ensues,  according  to  the  length  of  these  periods, 
in  one  or  other  direction,  a  certain  number  of  times.  Of  these  different  periods 
which  elapse  between  the  moment  of  stimulation  and  that  in  which  the  deviation 
coinmences  to  manifest  itself,  the  shorter  serves  to  determine  the  rate  of  propa- 
gation according  to  the  formula  V  = 

A  rate  of  propagation  of  26'"  43  per  second  is  found,  that  is  to  say,  practically 
that  which  Bernstein  has  pointed  out  as  being  the  rate  of  propagation  of  the 
negative  variation  in  the  nerves  of  the  frog. 

In  comparing  these  different  periods  one  with  another  we  see  that  a 
"(T7o  to  -gJo  of  a  second  =  O"""  00134  =  t. 

After  the  formiila  V  t=  X  (length  of  wave) 

26-43  X  yJ^g  =  0'"  035  ;    whence  J  X  =  IT"""""'  5. 

The  length  of  a  wave  =  3"="'*  J. 

The  frequency  or  number  of  oscillations  per  second  =  750  circa. 

Nature  of  the  phenomenon. — It  may  be  asked  if  this  oscillatory  phenomenon 
represents  the  negative  variation  (cm'rent  of  action),  or  an  electrotonic  modifica- 
tion of  the  nerve  (polarization  at  a  distance),  both  being  thus  proved  to  be  less 
simple  than  has  hitherto  been  supposed.  The  author  of  these  researches  main- 
tains that  it  is  not  an  electrotonic  phenomenon,  but  a  negative  variation. 

Nervous  interferences. — Inasmuch  as  the  nerve  is,  throughout  its  length,  the 
seat  of  a  series  of  waves  which  pass  along  it,  and  inasmuch  as  we  are  able  to  cause 
these  waves  to  act  on  a  rheoscope,  it  will  be  possible  for  us  to  make  them  act  on 
it  in  such  a  manner  that  they  interfere  with  one  another  in  definite  fashion.  In 
order  to  accomplish  this,  two  points  of  a  nerve  are  chosen  sejoarated  from  one 
another  by  a  wave  length  or  half  a  wave  length,  and  these  two  points  are  con- 
nected to  the  same  electrometer  or  to  the  same  galvanoscopic  paw.  In  the  first 
case  (a  wave  length)  the  phases  will  be  concordant ;  they  will  supplement  one 
another  in  order  to  produce  an  electromotor  effect,  there  will  be  a  stronger  devia- 
tion of  the  instrument  or  a  stronger  contraction  of  the  frog's  foot  ;  in  the  second 
case  (half  a  wave  length)  the  phases  will  be  discordant  and  opposed,  they  will 
neutralize  each  other  ;  there  will  be  immobility  of  the  instrument  and  repose  of 
the  frog's  foot. 

Electrical  resistance  of  the  nerve.  —  Compared  to  a  rod  of  copper  having  the 
same  form  and  dimensions,  a  nerve  is  a  very  inferior  conductor.  The  numerical 
estimations  which  have  been  made  of  its  resistance  have  no  great  value,  because 
its  electrically  active  substance  may  be  extremely  reduced  with  regard  to  the 
protective  or  nourishing  materials  which  enter  into  the  composition  both  of  the 
nerve  and  of  its  constituent  elements.  It  is  as  if  a  tube  of  copper  were  compared 
to  a  similar  tube  of  paraffin  containing  extremely  fine  copper  wires  in  its  interior. 
The  most  interesting  observation  is  the  determination  of  the  variations  of  this 
resistance  as  regards  their  connexion  with  the  activity  of  the  nerve.  Charpen- 
tier has  found  that  the  electrical  resistance  of  the  nerve  increases  with  its  activity  ; 
and  that,  on  the  contrary,  it  diminishes  when  its  physiological  properties  disappear. 


84  ELEMENTARY  NERVOUS  FUNCTIONS 

Cocaine  diniinislies  it,  curare  and  strychnine  at  first  diminish  it  for  sometime, 
but  afterwards  increase  it ;  crushing  of  the  nerve  causes  it  to  fall  by  a  half.  This 
increase  in  resistance  of  the  nerve  during  activity  is  attributable,  according  to 
this  author,  to  the  development  of  an  opposing  electromotive  force  which  repre- 
sents the  physiological  work  (the  expenditure  of  energy  of  the  nerve)  and  serves 
to  estimate  it ;  he  has  found  in  one  experiment  that  this  expenditure  is  equal 
^^  a^oooVo 0(7  of  a.  kilogrammetre. 

No  lateral  influence.  —  The  electric  currents  whose  intensity  is  capable  of 
changing  so  abruptly  are,  in  consequence  of  this  faculty,  liable  to  induce  currents 
in  circuits  in  their  neighbovirhood,  if  special  precautions  are  not  taken  to  avoid 
this  influence  at  a  distance. 

Can  the  currents  of  action  of  one  fibre  excite,  by  influence,  currents  in  a  neigh- 
bouring fibre  ?  Experience  reiDlies  in  the  negative,  and  the  least  reflection  shows 
that  this  must  be  so,  otherwise  nerves  would  discharge  various  and  independent 
functions  and  would  never  act  except  simultaneously. 

Part  played  by  the  cell  in  the  transmission  of  excitation. — The 
impulse,  in  travelling  from  the  receptive  to  the  distributive  pole  of 
the  neuron,  passes  through  the  body  of  the  cell.  Does  it  undergo 
some  modification  in  it  ?  This  has  been  maintained,  and  the  majority 
of  neurologists  still  maintain  it  as  a  matter  about  which  no  discussion 
is  allowable.  I  consider  that  experiment  and  reasoning  both  support 
the  opposite  thesis. 

(a)  Arguments  draivn  frotn  analogy. — In  the  muscidar  element,  it  is  not  the 
granular  protoplasm  surroianding  the  nucleus  which  represents  the  contractile 
fimction,  but  rather  its  external,  differentiated,  striated  portion  ;  in  the  neuron, 
the  differentiated  function,  strictly  called  nervous,  is  not  that  which  surrounds 
the  nucleus,  but  rather  consists  in  the  fibres  to  which  this  mass  gives  origin,  and 
which  pass  through  it  in  order  to  proceed  to  a  greater  or  less  distance. 

(b)  Arguments  drawn  from  experiment. — There  are  neurons,  such  as  those  of 
the  posterior  root,  which  may  be  excited  at  will,  either  above  or  below  their  cell 
body  ;  it  is  impossible  to  observe  any  real  and  constant  difference  in  the  effects 
of  these  stimulations  ;  the  cell  produces  no  change  in  them,  neither  in  the  in- 
tensity, nor  the  latent  period,  and  neither  the  form  nor  the  distribution  of  the 
impulses  is  altered  by  it.  Changes  of  this  order,  on  the  other  hand,  become 
marked  when  the  impulse  passes  from  one  neuron  to  another  in  the  felt  works 
of  the  grey  medullary  matter.  The  experiment  has  been  made  on  the  frog 
(Morat). 

Bethe  has  performed  a  still  more  convincing  experiment.  Taking  advantage 
of  the  fact  that,  in  certain  animals,  as  the  crab,  these  cells  are  attached  to  fibres 
by  long  pedicles  arranged  parallel  to  each  other  and  perpendicularly  to  the  fibres, 
he  cuts  these  pedicles,  and  thus  at  the  same  time  separates  the  cells,  while  preserv- 
ing the  continuity  of  the  fibres  throughout  their  length.  The  transmission  of 
the  impulses  and  the  refiex  movements  to  w^hich  they  give  rise  remain  possible 
for  several  days.  Functional  activity  ceases  at  the  end  of  this  period,  on  account 
of  the  degeneration  which  the  nerves,  isolated  fron^  their  troiihic  cells,  undergo. 
This  experiment  proves  both  the  independence  of  the  fibres  with  regard  to  the 
cells  so  far  as  concerns  the  external  or  nervous  function  of  these  fibres,  and  their 
dependence  so  far  as  concerns  the  maintenance  of  their  nutrition. 

Exner  (previously  to  the  preceding  authors)  had  studied,  by  the  galvano- 
metric  method,  the  influence  of  the  cells  of  the  spinal  ganglia  on  the  transmission 
of  impulses  by  the  posterior  roots.     These  roots,  cut  very  close  to  the  spinal 


NERVE  ENERGIES  85 

cord,  are  connected  by  their  end,  tlxus  divided,  to  a  galvanometer  ;  a  stimulus  is 
applied  to  the  nerve  below  the  ganglion  ;  the  transmission  of  the  impulse  is 
effected  through  the  ganglion  just  as  through  an  ordinary  nerve,  there  being  no 
exaggeration  of  the  latent  period. 

Contradictory  experiments. — On  the  other  hand.  Gad  and  Joseph,  experiment- 
ing on  the  jugular  ganglion  of  the  vagus,  regarded  as  a  spinal  ganglion,  and  taking 
the  respiratory  movements  as  evidence  of  the  reaction,  have  found  that  there  is 
a  difference  in  the  duration  of  the  period  of  latency  when  the  excitations  are 
made  below  or  above  the  ganglion.  According  to  these  authors,  the  delay  in 
the  first  case  is  from  0"123  of  a  second,  in  the  second  from  0'087  ;  the  difference 
of  0'036  between  the  two  indicates  the  delay  iindergone  by  the  impulses  in  their 
transit  tlirough  the  ganglion. 

The  structiu'e  of  these  ganglia,  in  reality  less  simple  than  was  at  first  believed, 
will  perhaps  serve  to  explain  these  divergencies. 

The  following  experiment  has  also  been  performed.  Let  an  isolated  segment 
of  the  spinal  cord  be  prepared,  and  let  all  the  sensory  and  motor  nerves  be  cut, 
with  the  exception  of  one  of  these  latter.  This  root  is  stimulated  between  the 
cord  and  the  muscles  which  it  supplies.  The  muscular  contraction  is  registered. 
Then  this  root  is  cut  close  to  the  spinal  cord  ;  the  stimulus  is  again  applied  and 
once  again  the  muscular  contraction  is  registered.  According  to  Cyon,  the  first 
of  the  two  contractions  is  longer  than  the  second  ;  this  he  attributes  to  a  re- 
flexion of  the  impulse  which,  starting  from  the  point  of  stimulation,  reascends  to- 
wards the  cord,  redescends  the  same  and  arrives  at  the  muscle  immediately  after 
the  direct  wave,  in  such  a  manner  as  markedly  to  lengthen  it.  Now  I  have  re- 
peated this  experiment  very  carefully,  but  I  have  never  found  any  appreciable 
difference  between  the  contractions  in  the  two  conditions. 

Modifications  of  the  body  of  the  cell  during  repose  and  functional  activity. — 
The  functional  activity  and  the  nutrition  of  the  organs  of  cells  are  two  things 
which  nvAy  in  principle  be  distinguislied.  One  is  often  observed  to  be  exagger- 
ated, while  the  other  is  diminished,  and  conversely  ;  but  their  limits  are  not 
clearly  defined  and,  fundanaentally,  they  are  reciprocally  connected.  Activity 
of  nerve  elements  is  manifested,  not  merely  by  changes  external  to  themselves 
(motion  and  sensation),  but  also  by  visible  modifications  of  the  protoplasm  of 
the  nerve  cell.  These  modifications,  consisting  in  change  of  volume  of  the  cell, 
displacement  of  the  nucleus,  re-ai'rangement  of  the  cliromatic  substance,  ha^'e 
been  studied  by  a  large  number  of  authors  on  different  objects,  such  as  the  grey 
matter  of  the  bulb,  the  ganglia  of  the  great  sympathetic,  the  retina,  etc.  The 
conclusions  are  slightly  different,  and  sometimes  contradictory  the  one  to  the 
other.  Lugaro,  who  has  undertaken  critical  investigation  of  the  question, 
maintains  that  the  cell  increases  in  size  when  subjected  to  moderate  excitation 
(electrical),  while  it  again  diminishes  if  the  excitation  is  excessive.  Speakuig 
generally,  an  organ,  when  it  becomes  active,  tends  at  the  same  time  to  increase 
its  nutritive  reserves  by  a  compensatory  exaggeration  of  assimilation  over  dis- 
assimilation  ;  but,  should  the  work  be  excessive,  the  compensation  is  insufficient 
and  the  reserves  tend  to  become  exhausted. 

Chromatolysis. — Between  the  meshes  of  its  network  the  cytoplasm 
of  the  nerve  cell  contains  a  substance  which  is  stained  by  methylene 
blue  (chromatine  of  Nissl).  This  substance  is  regarded  by  histologists 
as  being  a  reserve  for  the  neuron  and  is  seen  to  disappear,  starting 
from  the  nucleus,  in  the  cells  of  the  nerves  which  have  been  fatigued 
by  stimulation  (Vas,  Mann,  Lambert,  Lugaro). 

To  the  phenomenon  of  the  disappearance  of  this  substance  the  name 


86  ELEMENTARY  NERVOUS  FUNCTIONS 

chromatolysis  has  been  given  ;   it  proceeds  jjari  passu  with  the  changes 
of  volume  of  the  cell  and  the  mechanical  displacements  of  the  nucleus. 
C.     EFFECTS  CONSECUTIVE  TO  STIMULATION  :    FATIGUE 

Definition, — The  word  fatigue  is  used  in  two  very  different  senses 
in  ordinary  language  and  in  that  of  physiology  respectively.  In  the 
first,  it  expresses  a  sensation  which  is  united  to  the  work  of  the  bodily 
organs  when  this  work  tends  to  become  excessive,  and  which  warns  us 
that  repose  is  necessary  ;  in  the  second,  it  expresses  not  merely  a  sen- 
sation, but  the  objective  phenomena  of  exhaustion  and  of  the  wear  and 
tear  of  these  organs,  which  checks  their  movement. 

Thus  the  excess  of  activity  tends  to  be  self-limited  ;  but  this  is 
effected  in  two  ways  :  the  one,  the  most  perfect,  in  which  the  regula- 
tion is  carried  out  by  a  complex  sequence,  the  nervous  system  inter- 
vening, and  in  which  we  once  more  observe  the  mutual  relationship  of 
motion  and  sensation  ;  the  other,  more  elementary,  in  which  work 
ceases  through  the  absence  of  materials  and  of  the  conditions  by  which 
it  can  be  supported. 

In  order  to  study  the  details  of  this  objective  phenomenon  of  ex- 
haustion, the  physiologist  excites  it  himself  in  the  different  organs, 
including  the  nerves,  by  putting  them  in  a  condition  which  involves 
prolonged  work.  But,  the  activity  of  the  nerve  being  estimated  by 
that  of  the  organ  to  which  it  communicates  the  impulse,  it  is  necessary 
to  have  recourse  to  certain  special  contrivances  in  order  to  estimate 
its  individual  fatigue  in  that  of  the  total  of  which  it  forms  a  part. 

Resistance  of  nerves  to  fatigue.  — When  the  stimulation  of  a  nerve 
(a  motor  nerve  for  example)  is  prolonged  beyond  a  certain  hmit,  which 
varies  according  to  circumstances,  the  contractions  decrease  and  finally 
disappear.  This  result  is  attributed  to  the  fatigue  arising  from  the 
wear  and  tear,  to  the  exhaustion  of  the  excitable  substance.  At  first 
it  was  supposed  that  this  fatigue  was  equal  in  the  nerve  and  in  the 
muscle.  Bernstein  has  proved  that  fatigue  is  far  more  marked  as 
regards  the  muscle  than  as  concerns  the  nerve. 

How  can  this  be  explained  ?  All  the  methods  employed  may  be 
reduced  to  the  following  :  the  transmission  of  the  impulses  between 
nerve  and  muscle  is  interrupted  for  a  certain  period  ;  the  work  of  the 
first  is  increased  vigorously  and  for  a  long  time  (in  other  words,  forced 
fatigue  is  induced),  while  the  second  remains  in  repose  ;  then  the  con- 
nexion of  the  nerve  with  the  muscle  is  re-established  (or  is  allowed  to 
re-establish  itself),  finally  it  is  observed  if  the  impulses  of  the  first  are 
transmitted  to  the  second.  If  this  is  so,  it  is  because  it  has  resisted 
the  fatigue  which  the  long  and  strong  stimulation  to  which  it  has  been 
submitted  has  not  failed  to  produce  in  the  muscle. 


NERVE  ENERGIES 


87' 


^«  N 


Fig. 


40. — Indefatigableness 
the  nerves. 


of 


Temporary  dissociation  of  the  muscular  and  nervous  tissues.  —  What  means- 
are  there  for  effecting  this  interruption,  which  should  be  only  temporary  ?  There 
are  two  :  the  action  of  the  continuous  current,  and  that  of  certain  special  poisons. 
Bernstein,  and  after  him  Wedinski,  have  brought  about  the  temporary  interrup- 
tion by  exciting  a  state  of  electrotonus  in  the  nerve  at  its  entrance  into  the 
muscle  for  a  determinate  time.  Bowditch  made  use  of  ciu-are,  which  is  deemed 
to  act  only  on  the  terminations  of  motor  nerves,  and  Lambert  has  employed 
atropine,  which  acts  in  the  same  w^ay  on  the  nerves  of  the  glands,  in  experiments 
carried  out  on  secretory  nerves.  The  removal  of  the  obstacle  takes  place  by 
the  gradual  and  spontaneous  elimination  of  the  poison.  If  the  stimulation  of 
the  nerve  is  maintained  throughout  the  cku'ation 
of  the  poisoning  by  curare  or  atropine,  it  is  sur- 
prisiiig  to  see,  when  this  poisomng  ceases,  that 
the  muscle  contracts  and  the  gland  secretes, 
thus  proving  the  transmission  of  the  impulse, 
and  therefore  the  absence  of  fatigue,  in  this 
nerve  which  has  been  kept  so  long  in  activity. 
But  does  poisoning  by  curare  or  atropine,  as 
also  the  action  of  the  constant  current,  respond 
to  a  simple  interruption  between  the  nerves  and 
the  organs  which  manifest  changes  in  them,  or 
» has  the  nervous  element  become  the  seat  of 
inertia  throughout  its  length  ;  in  which  case  it 
would  be  no  longer  susceptible  of  stimulation 
and  fatigue  ?  Herzan  prefers  this  second  ex- 
planation, which  he  supports  by  experiments 
made  on  animals  convulsed  by  strychnine  ; 
indeed,  in  these  animals  the  nerve  appears  as 
inexcitable,  and  consequently  as  fatigued,  as 
the  muscle  itself. 

Wedinski,  in  order  to  eliminate  these  errors, 
investigates  the  activity  of  the  nerve  in  a  direct 
manner,  by  its  negative  variation,  estimated  by 
the  aid  of  the  galvanometer  or  the  telephone  ; 
he  finds  that  this  variation  exists  so  long  as 
does  stimiilation  itself,  proving  thus  once  again 
the  inde fatigability,  which  is  at  least  relative, 
of  the  nerve. 

Another  method. — In  the  preceding  experi- 
ments it  is  assumed  that  the  agent  (curare, 
atropine,  electrotonization,  etc.)  made  use  of  in 

order  to  physiologically  separate  the  nerve  from  the  muscle,  localizes  its  action 
upon  a  definite  and  restricted  area  of  the  first  (for  example,  ciirare  on  the 
motor  plate)  exclusively,  and  that  the  rest  of  the  nerve  preserves  its  normal 
activity,  although  hindered  from  manifesting  it  on  account  of  its  separation 
from  the  muscle.  But  it  is  possible  that  this  hypothesis  is  inaccurate.  Claude 
Bernard  maintained  that  curare  acts  electively  on  the  whole  motor  nerve  ; 
electrotonus  is  undoubtedly  transmitted  to  a  certain  distance ;  and  we  do  not 
know  if  the  interior  activity  of  a  nerve,  separated  from  its  muscle,  is  precisely 
the  same  as  that  of  a  nerve  which  has  preserved  its  natural  connexions  with  it. 

For  all  these  reasons,  Carvallo  has  had  recourse  to  a  method  different  to  the 
preceding,  by  which  fatigue  of  the  muscle  and  of  the  nerve  may  be  separately 
made  evident.  Two  muscles  of  like  nature  and  supplied  with  their  nerves  are 
kept  exactly  at  the  same  fixed  temperature.     During  this  time  one  of  the  nerves 


Two  muscles,  Mj,  Mo,  furnished 
with  their  nerves  N„  No,  are  simul- 
taneously stimulated  at  x,  by  an 
induced  current.  The  nerve  N2  is 
anelectrotonized  at  B  by  a  constant 
current  Z,  so  as  to  prevent  the 
impulse  reacliing  the  muscle  M2,  thus 
to  prevent  this  muscle  being 
fatigued.  The  mu-scle  M 1  is  quickly 
fatigued  and  ceases  to  contract. 
If  then  the  cell  current  be  broken, 
while  the  stimulation  of  the  two 
nerves  continues  at  x,  the  muscle 
M2  wiU  be  seen  to  contract  ;  there- 
fore its  nerve  has  not  felt  the  effects 
of  fatigue. 


88  ELEMENTARY  NERVOUS  FUNCTIONS 

is  subjected  to  temperatures  varying  from  0°  to  30°,  while  all  that  happens  from 
10°  to  10°  is  carefully  noticed  :  it  is  ascertained  that  there  is  a  temperature  most 
Javourable  for  the  motor  nerve  of  the  frog,  which  is  20°.  Above  and  below  this 
temperature  the  susceptibility  of  the  nerve  decreases.  The  chilled  nerve  becomes 
fatigued  more  rapidly  than  the  nerve  at  20°.  In  a  repeated  series  of  excitations, 
it  is  noticed  that  the  decrease  of  the  contractions  (the  curve  of  fatigue)  is  brought 
about  so  much  the  more  quickly  as  the  temperature  is  lower.  But  the  nerve  at 
0°  and  fatigued  by  stimulation  recovers  without  delay  its  first  excitability  when 
the  temperature  once  again  becomes  favourable  to  it ;  that  is  to  say,  when  stimu- 
lated, the  temperature  produces  in  the  muscle  work  equal  to  that  which  this 
organ  produced  before.  This  result  clearly  shows  that,  although  diiring  the 
time  that  it  was  chilled,  the  nerve  was  fatigued  independently  of  the  muscle,  and 
merely  from  the  fact  of  the  conditions  of  temperature  in  which  it  was  placed  ; 
the  muscle,  kept  during  this  time  at  the  same  temperature,  had  no  reason  to 
undergo  the  effects  of  fatigue.  Hence,  in  these  conditions,  and  according  to  the 
conclusions  of  the  author,  fatigue  would  appertain  to  nerves,  but  not  to  muscles. 

These  experiments  have  also  shown  that,  when  a  nerve  is  chilled  to  0°  over 
a  certain  limited  portion  of  its  course,  and  is  fatigued  by  successive  excitations, 
the  portion  thus  chilled  and  fatigued  (locally  inexcitable)  nevertheless  conducts 
the  impvilse  just  as  the  non-chilled  and  non-fatigued  portions.  This  fact  supports 
the  view  of  the  non-identity  of  the  two  processes  of  excitation  and  conduction. 

Conclusion. — From  the  fact  that  heat  has  a  similar  influence  on  the  excitability 
of  nerve,  it  must  be  concluded  that  this  phenomenon  of  excitability  (if  not  that 
of  conductivity)  is  fundamentally  of  a  chemical  and  not  of  a  purely  physical 
nature,  in  spite  of  the  small  quantity  of  energy  which  is  made  use  of  in  producing 
it.  The  indefatigability  of  the  nerves  is  only  a  smaller  degree  of  fatigability 
in  comparison  with  the  muscles. 

The  mechanism  of  neuro-muscular  fatigue. — Muscular  or  nervous  fatigue  is 
usually  attributed  to  the  exhaustion  of  cellular  elements  which  have  been  func- 
tionally active  for  too  long  a  time.  Abelous  remarks  that  this  fatigue  arises 
partly  from  the  products  of  disintegration  formed  by  this  very  activity,  which 
act  as  paralysing  or  strictly  speaking,  "  curarizing  "  substances  on  the  nerve 
element.  These  waste  products  formed  by  muscle  act  on  the  motor  nerve  termi- 
nations by  a  kind  of  auto-cur arization.  When  the  nerve  is  subjected  to  the 
action  of  a  tetanizing  current,  a  moment  arrives  in  which  the  contractions  cease 
to  occur  ;  but  if  then  the  muscle  be  directly  stimulated,  the  latter  is  observed 
to  respond  to  the  stimulus  ;  this  is  practically  the  same  result  as  is  obtained 
with  ciirare,  except  that  the  paralysing  substance  is  in  this  case  elaborated 
locally  as  the  result  of  the  muscular  "  chimisme  "  during  contraction.  Fatigue 
rapidly  occurs  in  the  case  of  individuals  or  animals  whose  suprarenal  capsules 
are  diseased  (Addison's  disease)  or  removed.  It  would  thus  be  a  function  of 
these  organs  to  neutralize  the  curarizing  or  paralysing  action  of  muscular  waste 
products.  (Abelous,  Charrin  and  Langlois.)  See  also  Albanese,  Arch,  of 
Biology,  1892. 

D.     ELECTROTONUS. 

The  term  electrotonus  is  applied  to  two  orders  of  phenomena,  the 
one  physical  (polarization),  the  other  physiological  (modifications  of 
excitability),  which  take  origin  in  this  nerve  when  it  is  traversed  by  a 
current.  For  some  (du  Bois-Reymond,  Pfliiger),  there  would  be  a 
close  connexion  between  the  two  orders  of  phenomena  ;  for  others 
(Matteucci,  Hermann),  they  would  be  entirely  independent.  What- 
ever the  facts  may  be  concerning  this  possible  relation,  the  term  elec- 


NERVE  ENERGIES  89 

trotonic  condition  should  be  reserved  for  the  physical  modification,  and 
that  of  electrotonus  for  the  physiological  modification  of  the  nerve  ; 
nevertheless,  the  two  expressions  are  made  use  of  indifferently  in  order 
to  indicate,  either  the  physical  modification,  or  the  physiological  modi- 
fication which  arises  from  the  passage  of  the  current. 

1.  Electrotonic  Condition.— Let  a  piece  of  nerve  of  a  certain  length  be 
taken  ;  it  is  placed  on  the  two  non-polarizable  electrodes  of  a  constant  ciuTent, 
in  such  a  manner  that  it  extends  beyond  tliem  on  both  sides,  away  from  the 
portion  submitted  to  the  action  of  tlie  current.  Three  areas  may  be  defined  in 
this  piece  of  nerve  :    one  intrapolar  and  two  extrapolar. 

If  the  portion  of  nerve  arranged  in  this  manner  were  an  ordinary  conductor 
(or  if,  tlirough  crushing,  it  had  lost  its  nervous  structm-e),  the  cuiTcnt  would 
circulate  only  in  the  intrapolar  portion.  If  it  were  a  nerve  in  which  both  its 
structure  and  its  vitality  are  preserv^ed,  in  addition  to  the  current  which  cir- 
culates in  the  intrapolar  portion,  electromotive  forces  will  be  developed  in  the 
extrapolar  portions  which  will  give  rise  in  them  to  differences  of  potential  be- 
tween different  points  of  its  length,  in  such  a  way  that,  if  two  of  these  points 
be  connected  with  the  galvanometer,  the  existence  of  a  current  will  be  demon- 
strated. 

Historical. — Longet  and  Guerard  were  the  first  who  observed  that,  when  a 
certain  length  of  nerve  is  subjected  to  the  action  of  the  current  of  a  battery,  a 
cvurent  is  developed  (which  they  call  derived)  in  the  extrapolar  region  of  the 
nerve  (Longet,  Anat.  and  Physiol,  of  the  Nervous  System  of  Man,  1. 1,  1842,  p.  143). 
Matteucci,  Gruenhagen,  Hermann  have  endeavoured  to  establish  the  theory  of 
these  derivations,  which  they  essentially  attribute  to  the  existence  of  a  difference 
of  electrical  conductivity  between  the  superposed  layers  of  the  nerve  or  of  the 
nervous  element.  Du  Bois-Reymond  has  studied  the  phenomenon  in  a  detailed 
manner.  He  endeavours  to  explain  it  by  his  molecular  theory"  (generally  aban- 
doned at  the  present  time).  Pfliiger,  Chauveau  and  many  others  after  them 
have  studied  the  modifications  of  excitability  of  the  nerve  which  accompany 
electrotonic  currents. 

The  terminology.  —  The  battery  cvirrent  (or  any  other  applied  to  the  nerve)  is 
called  the  excitiny  or  polarizing  current  ;  those  which  arise  in  the  extrapolar 
regions,  which  are  tlie  localities  influenced,  polarized  or  electrotonized,  and  in  one 
or  other  of  which  two  points  of  derivation  are  chosen  in  order  to  connect  them 
with  the  galvanometer,  are  called  derived,  electrotonic  currents,  or  currents  of 
polarization.  The  region  which  approximates  the  anode  (positive  pole  of  the 
battery  current)  is  called  anodic,  and  that  in  the  neighbourhood  of  the  cathode 
(negative  pole)  is  known  as  cathodic.  The  derived  current  in  each  of  the  respec- 
tive localities  is  known  as  anelectrotonic  or  anelectrotonus ,  and  catelectrotonic 
or  catelectrotonus. 

1.  Electrotonic  currents  :  direction,  duration,  intensity. — The  direction  of  the 
electrotonic  currents  is  the  same  as  that  of  the  polarizing  current  ;  their  intensity 
progressively  decreases  in  proportion  as  they  are  removed  from,  the  locality  excited 
in  the  two  extrapolar  regions.  These  characters  suffice  to  clearly  distinguish 
electrotonic  currents  from  the  current  of  action  or  negative  variation  of  the 
nerve,  of  which  the  direction  is  constant,  and  which  is  connected  with  the  state 
of  stimulation  of  the  nerve,  whatever  may  be  the  natiire  of  the  stimulus  and  the 
direction  of  the  exciting  current,  when  electricity  is  made  use  of. 

The  intensity  of  the  electrotonic  currents  further  varies  with  the  intensity  of 
the  polarizing  current  and  the  length  of  the  portion  polarized.  It  is  not  equal 
for  the  two  localities  excited,  but  anelectrotonus  is  stronger  than  catelectrotonus. 
Tliis  intensity  is  not  miiformly  maintained  dm-ing  the  passage  of  the  polarizing 


90  ELEMENTARY  NERVOUS  FUNCTIONS 

current,  but  varies  as  regards  the  two  extrapolar  portions:  catelectro tonus  at  once 
decreases,  wliile  anelectrotonus  progressively  increases,  and  then  itself  decreases. 

Interference  with  the  current  peculiar  to  the  nerve. — When  the  middle  segment 
of  the  nerve  is  chosen  for  the  space  acted  upon,  as  in  the  exjDeriment  which  has 
just  been  referred  to,  and  one  of  the  extremities  for  the  locality  of  derivation, 
this  latter  is  already  the  seat  of  a  current  of  definite  direction  (current  of  repose 
or  of  longitudinal-transverse  alteration)  whose  action  is  rendered  manifest  by 
the  galvanometer  ;  this  current  reinforces  algebraically  the  electrotonic  current, 
which  inay  be  much  stronger  than  itself,  and  which  may  be  reinforced  or  weak- 
ened by  it,  accordingly  as  it  has  the  same  or  an  opposite  direction.  It  is  this- 
which  was  first  known  as  the  positive  and  the  negative  phase  of  electrotonus,  an 
incorrect  terminology,  inasmuch  as  the  electrotonic  current  is  altogether  inde- 
pendent of  the  current  of  repose  of  the  nerve.  In  order  to  demonstrate  it,  it  is- 
merely  necessary  to  modify  the  arrangement  of  the  experiment,  and  to  replace 
the  derived  portion  by  the  influenced  portion,  and  reciprocally.  Derivation, 
investigated  on  the  median  segment  of  the  nerve  at  two  points  perfectly  iso- 
electric, presents  electrotonic  currents  when  one  of  the  extremities  is  stimulated,. 
and  these  cvirrents  still  follow  the  same  direction  as  the  polarizing  current,  with- 
ovit  any  complication  of  the  cvarrent  special  to  the  nerve. 

Rate  of  propagation. — Electrotonus  is  transmitted  from  the  portion  influenced 
to  the  derived  portion  at  a  rate  which  ajjpears  to  be  clearly  that  of  the  propaga- 
tion of  the  impulses  (du  Bois-Reymond  and  Bernstein)  ;  others,  it  is  true,  have 
maintained  that  its  development  is  instantaneous,  like  that  of  the  electric  current 
itself.  It  is  in  any  case  very  rapid,  and  hence  it  is  obvious  that  induced  ciu"rents- 
may  give  rise  to  it  just  as  do  the  continuous  current.  Chauveau,  Charbonnel- 
Salle  have  observed  it  to  ensue  after  discharges  of  static  electricity. 

2.  Paradoxical  contraction. — If,  instead  of  connecting  the  portion  influenced 
with  the  wires  of  a  galvanometer,  the  latter  is  brought  into  contact  with  the 
freshly  cut  nerve  of  a  galvanoscopic  paw,  and  electrotonus  is  produced  by  the 
current  of  a  battery  or  by  instantaneous  discharges,  at  every  passage  of  the 
current,  the  galvanoscopic  paw  is  observed  to  contract.  The  physical  rheoscope 
has  thus  been  replaced  by  a  physiological  rheoscope  which  receives  the  impulses, 
and  these  impulses  are  none  other  than  the  electrotonic  ciirrents  arising  in  the 
primary  nerve,  which  reach  the  cut  extremity  of  the  secondary  nerve  (nerve  of 
the  galvanoscopic  paw). 

The  paradox  consists  in  the  fact  that  the  excitation  of  the  first  nerve  seems  to 
be  transmitted  to  the  second,  in  violation  of  the  law  of  the  integrity  of  structure 
and  of  tliat  of  isolated  conduction. 

But  this  violation  is  only  apparent,  because,  of  these  two  laws  the  second 
applies  merely  to  the  nerves  which  have  not  been  cut,  and  the  first  is  verified 
by  the  fact  that,  if  the  two  nerves  are  placed  in  contact,  end  to  end,  contraction 
does  not  ensue,  the  electric  differences  to  which  electrotonus  gives  rise  being 
not  produced. 

Experiment. — The  experiment  in  its  classical  form  is  carried  out  in  the  following 
manner  :  two  principal  branches  of  the  sciatic  nerve  in  the  frog,  these  branches 
being  the  peroneal  and  the  nerve  to  the  gastrocnemius  are  prepared,  and  the 
trunk  of  the  sciatic  is  cut  in  the  thigh.  If  one  of  these  nerves  be  stimulated 
(derivations  being  avoided),  a  contraction  follows  not  only  in  its  own  muscle, 
but  also  in  the  muscle  of  the  other  nerve.  When  the  trunk  of  the  sciatic  is  not  cut, 
the  paradoxical  contraction  would  not  be  obtained,  but  reflex  contractions  more 
or  less  numerous,  which  wovild  be  recognized  by  their  much  longer  latent  period. 

Difference  between  the  paradoxical  contraction  and  the  indirect  or  secondary 
contraction. — The  paradoxical  contraction,  obtained  by  putting  nerve  in  contact 
with  nerve,  is  not  comparable  to  the  contraction  known  as  induced  or  secondary. 


NERVE  ENERGIES 


91 


Fig 


4 1 . — Paradoxical 
contraction. 


which  resiilts  when  nerve  is  brought  into  contact  with  muscle  (the  latter  being 

in  a  state  of  contraction). 

In  this  last  case,  it  is  the  negative  variation  of  the  muscle  stimulated  (by  elec- 
tricity or  otherwise)  which  is  the  excitant  of  the  gal- 

vanoscopic  paw  ;   in  the  first  it  is  electrotonus  only 

and    not    the    negative   variation   of    the   electrified 

nerve  which  excites  the  physiological  rheoscope.     The 

negative  variation  of  the  nerve  is  much  too  feeble  to 

give  rise  to  this  stimulation  ;  it  is  for  this  reason  that 

mechanical    or  chemical   excitation  of  the  nerve  is 

always  without  effect  on  the  secondary  nerve.     Elec- 

trotonic  currents  which  are  susceptible  of  being  much 

stronger    than  the  negative  variation  have,  for  this 

reason,  a  definite  exciting  effect. 

Inequality  of  the  phases. — With  equal  intensity  of 

the  polarizing  current,  we  have  seen  that  the  electro- 
tonic  ciu-rents  are  unequal  ;  polarization  in  the  region 

of  the  anode  exceeds  that  which  arises  in  the  region  of 

the  cathode,  independently  of  the  cvu-rent  of  repose, 

which   is  diminished  or   reinforced  according  to  the 

direction  of   the  polarizing  current  ;    it   thus  follows 

that  when  alternating    currents  which  are  equal  and 

not  too  strong  succeed  one   another  with  a   certain 

frequency,  the  resulting  effect  will  manifest  itself  by 

a  feeble  anelectrotonic  current.     This  current  must 

not  be  confounded  with  the  negative  variation,  such 

as  may  itself  arise  from  the    emj^loyment  of  the  so- 
called    tetanizing    cxrrrents.       Charbonnel-Salle    has 

proved  that  the  electrotonic   state  may  be  induced 

by  short  currents   by  the  aid  of  ■  the  electrometer  of 

Lippmann,  and  has  also  proved  that,  in  these  con- 
ditions, the  same   regulative   laws   are   in   action  as 

when  it  is  produced  by  continuous  currents. 

Difference     between     electrotonus    and     negative 

variation. — Electrotonus  and  negative  variation  have 

this  in  common,  that  they  are  transmitted,  both  of 

them,  through  the  length  of  the  nerve  outside  the  portion  influenced  by  the  excit- 
ing current  ;  both  depend  on  the  integrity  of  the  structure  of  the  nerve,  and  they 
disappear  when  the  latter  has  been  tied  or  crushed  between  the  portion  influenced 
and  that  which  is  derived.  On  the  other  hand,  they  are  distinguished  from 
each  other  by  the  three  following  characters  :  (1)  the  electrotonic  modification 
may  be  demonstrated  by  connecting  two  isoelectric  points  of  the  nerve  to  the 
galvanometer,  while  negative  variation  is  only  observed  when  two  points  of  a 
different  iDotential  are  thus  connected  ;  (2)  the  electrotonic  tnodifi cation  progres- 
sively decreases  with  the  distance  between  the  portion  influenced  and  the  derived 
portion,  while  the  intensity  of  the  negative  variation  remains  the  same  ivhatever 
length  of  nerve  may  be  interposed  between  the  point  excited  and  the  extremity  on 
which  the  derivation  is  taken  ;  (3)  electrotonic  variation  is  definitely  related  to 
the  direction  of  the  influencing  current,  while  negative  variation  has  a  du'ection 
independent  of  that  of  the  cm-rent  made  use  of  to  excite  the  nerve. 

3.  Theories  of  electrotonus. — Tlie  electrotonic  current  originates  in  a  polariz- 
ation which  the  exciting  current  produces  in  the  extrapolar  regions.  This 
polarization  is  differently  interpreted  by  different  authors. 

Soine,  as  du  Bois-Reymond,  regard  it    (althougli  connected  with  the  special 


Let  there  be  a  cut  nerve 
trunk  AB,  whence  are  given 
off  two  branches  BC  and  BM, 
the  latter  going  to  the 
muscle  M.  If  the  branch 
BC  which  is  not  in  physio- 
logical connexion  with  the 
muscle  M,  be  stimulated  at 
C,  tliis  latter  muscle  will  be 
seen  to  contract. 

Several  equivalent  forms 
may  be  given  to  this  ex- 
periment and  two  nerve 
tnmks,  of  which  one  is  fur- 
nished with  its  muscle, 
may  be  coupled  together. 
The  only  necessary  condition 
is  that  there  should  be  con- 
tact between  them  for  a  cer- 
tain length. 


92 


ELEMENTARY   NERVOUS   FUNCTIONS 


structvire  of  the  nerve)  as  beiiig  of  purely  physical  nature,  and  of  the  same  kind 
as  that,  though  much  more  complicated,  which  is  presented  by  the  molecules 
of  soft  iron  when  a  current  is  made  to  pass  through  the  latter  ;  others,  as  Mat- 
teucci,  Hermann,  look  upon  it  as  the  result  of  the  chemical  phenomenon  of  elec- 
trolysis due  to  the  difference  of  electrical  conductivity  of  the  different  parts  of 


Nerve 


Ane^eetrotnnie 
(Uirrent 


Po^nrisinf 
Current 


Cate'ertrotonic 
Current 


Pig.   42. — Polarization  of  the  nerve  in  its  two  extrapolar  segments  and  production  of 
electrotonie  currents  in  these  two  segments. 

The  middle  region  is  traversed  by  a  constant  current  (polarizing  current).  The  extrapolar 
regions  show  currents  of  polarization  of  the  same  direction  as  the  preceding,  but  unequal  in 
intensity.     The  anelectro tonic  current  is  more  intense  than  the  catelectrotonic  current. 

the  nerve,  or  rather  of  the  nerve  element,  the  axis  cylinder  being  a  much  better 
conductor  than  the  myelin.  If  a  current  is  sent  through  the  badly  conducting 
investing  sheath,  at  the  point  of  contact  with  the  two  bodies  a  polarization  arises 
(the  opposed  current  increasing  the  resistance  to  the  passage  of  the  current  from 
the  sheath  to  the  axis  cylinder).  On  account  of  this  resistance,  the  current 
spreads  to  right  and  left  from  its  point  of  application  to  the  ramifications,  and 
distributes  genuine  derived  currents  having  the  same  direction  as  the  current 
of  the  battery,  and  which  progressively  diminish  in  intensity  in  joroportion  as 
the  distance  from  the  points  of  application  of  the  princijDal  current  becomes 
greater  ;  these  are  the  currents  which  are  received  by  the  galvanometer  con- 
nected with  the  nerve  and  which  represent  the  electrotonie  currents. 

Nerves  of  different  structure. — In  the  non-myelinated  nerves  electrotonus  is 
generally  wanting  (Biedermann)  ;   yet  this  absence,  is  not  total  (Borvittau)  ;    the 


y 


Fig.  43. — Internal  polarization  of  a  narve  fibre,  giving  rise  to  an  electrotonie  current 
in  the  extrapolar  region.  Only  one  of  the  influencing  po'.es  is  represented  (after 
Waller). 

,A,  axis  cylinder  ;  MM,  myelin  ;  bb,  surface  of  contact  between  A  and  M,  where  it  is  supposed 
that  the  polarization  gives  rise  to  a  resistance  which  obliges  the  current  to  diffuse  itself  following 
this  surface.  The  intensity  of  the  polarization  progressively  diminishes,  starting  from  the  point 
of.'appUcation  of  the  pole  under  consideration  of  the  influencing  current. 

difference  is  merely  quantitative  (Mendelssohn),  qualitatively  the  phenomena 
are  the  same. 

The  non-myelinated  nerves,  generally  little  experimented  uj)on,  are  thvis  parti- 


NERVE  ENERGIES  93 

cvilaiiy  well  adapted  for  the  study  of  negative  variation  without  the  complication 
of  electrotonus. 

Integrity  of  structure.  Electrotonus  disappears  when  the  nerve  is  crushed 
between  the  portion  influenced  and  that  derived,  as  Longet  has  observed. 

Schematic  reproductions.  —  By  means  of  special  apparatus,  it  is  possible  to 
reproduce  the  principal  phenomena  of  electrotonus,  as  has  been  done  by  Mat- 
teucci,  Gruenhagen,  Hermann.  And  it  may  be  maintained  that  the  essential 
and  very  simple  conditions  of  these  schemes  are  reproduced  in  the  nerve  ;  but 
others  also  arise  in  this  latter  by  which  electrotonus  is  assimilated  to  the  mani- 
festations of  organized  tissues. 

It  is  thus  that  this  phenomenon  disappears  in  the  case  of  the  dead  nerve,  and 
when  the  latter  has  degenerated  (Schiff ,  Valentin),  that  it  diminishes  or  disappears 
for  a  longer  or  shorter  time  under  the  influence  of  anaesthetics  (Waller,  Bieder- 
mann). 

Consecutive  effects. — Post-electrotonic  current.  —  Before  whollj^  disappearing 
at  the  breaking  of  the  polarizing  current,  electrotonus  is  first  followed  by  an 
inversion  of  the  direction  of  the  cmrent  (Fick),  w^iich  is  clearly  demonstrable 
only  in  anelectrotonus  (Hermann). 

2.  Electrotonus.  Modifications  of  Excitability.- — The  polar- 
izing current,  whose  effects  are  exerted  either  on  the  interpolar  region 
or  on  the  neighbouring  locahties  situated  outside  its  poles,  causes  in  it 
similar  local  modifications  of  excitability,  whose  general  tenor  has  more 
than  one  relationship  to  the  physical  effects  which  are  produced  by  it. 
In  order  to  study  these  modifications,  the  nerve  is  left  in  connexion 
with  its  muscle  ;  by  its  other  extremity  it  may  be  connected  or  not 
with  its  centre.  The  polarizing  current  passing  through  its  middle  or 
interpolar  segment,  the  extrapolar  segment  in  connexion  with  the 
muscle  will  be  described  as  myopolar  ;  the  other  will  be  called  ceiitro- 
polar.  When  the  influencing  current  follows  the  same  direction  as 
that  taken  by  the  impulses  which  proceed  to  the  muscle,  it  wall  be 
called  descending  :    the  cathode  (negative  pole)  is  then  on  the  side  of 


r€ 


*    I    -  n  ui 

Fig.   44. — Post-electrotonic   intrapolar   currents   produced   after   the   cessation   of    the 
polarizing  current  (after  Waller). 
I,  polarizing  current  ;   II,  ordinary  post-current  of  contrary  direction  ;   III,  post-ciurent  whose 
direction  is  tlie  same  as  that  of  the  polarizing  current.  .^ 

the  muscle  and  the  myopolar  segment  is  in  a  condition  of  catelec- 
trotonus  ;  while  the  anode  (positive  pole)  is  on  the  side  of  the  centres 
and  the  centropolar  segment  is  in  a  condition  of  anelectrotonus.  On 
the  other  hand,  it  is  called  ascending  when  the  cathode  and  the  seg- 
ment in  a  state  of  catelectrotonus  are  on  the  side  of  the  centre  ;  the 
anode  and  the  segment  in  a  state  of  anelectrotonus,  on  the  side  of  the 
muscle. 


94 


ELEMENTARY  NERVOUS  FUNCTIONS 


Proof  of  Excitability. — The  local  excitability  of  the  different  points  of  the 
different  segments  will  be  investigated  before,  during  and  after  the  passage  of 
the  influencing  current.  By  experimenting  with  short  excitations,  the  increased 
or  diminished  effects  of  the  latter  will  then  be  demonstrated  by  muscular  con- 
tractions, which  may  be  registered  in  order  that  they  may  be  compared  one  with 
another.  In  the  extrapolar  regions,  electric  stimulation  may  be  applied  without 
any  difficulty  by  means  of  induced  ciu-rents  ;  in  the  intrapolar  region,  this  excita- 
tion may  be  effected  either  by  electricity,  certain  precautions  being  taken  so 
that  the  polarizing  current  be  not  deranged,  or  mechanically  or  chemically. 

Sketched  out  and  successively  investigated   by   Ritter,   Nobili,   Matteucci, 
Valentin,  and  formulated  as  regards  its  essential  points  by  Eckhard,  the  study 
of  electrotonus  has  been  completed  and  perfected  by  the  extensive  and  very 
methodical  work  of  Pfliiger. 

General  formula. — If  it  be  assumed  that  the  middle  portion  of  the 
nerve  be  traversed  by  a  current  whose  intensity  is  described  as  medium, 
the  excitabihty  of  the  nerve  is  modified  throughout  its  extent.  It  is 
increased  in  the  neighbourhood  of  the  negative  pole  (cathode)  :  this  is 
catelectrotonus  ;  it  is  diminished  in  the  neighbourhood  of  the  positive  pole 
(anode)  :    this  is  anelectrotonus. 

The  nerve  is  thus,  as  it  were,  divided  into  two  regions,  the  one  of 
increased  excitabihty,  the  other  of  diminished  excitabihty ;  these 
regions  being  separated  by  a  point  called  neutral  or  indifferent,  situated 
in  the  intrapolar  region,  which  preserves  its  initial  excitability. 

Positive  and  negative  modifications. — The  modification,  whether 
positive  or  negative,  attains  its  maximum  at  each  pole  (positive  at  the 
negative,  and  vice  versa)  and  thence  progressively  decreases  in  the 
neighbouring  extrapolar  region,  as  also  in  the  portion  of  the  intra- 
polar region  which  is  adjacent  to  the  pole  in  question.  A  curve  in  the 
form  of  an  S  placed  horizontally,  surrounding  the  nerve  as  an  axis, 
expresses,  in  a  sufficiently  graphic  manner,  these  modifications,  save 
that  the  extremities  are  strongly  inflected  on  the  outside,  the  decrease 
of  the  modification  being  effected  by  a  much  more  gradual  incline  in 
the  extrapolar  regions  than  in  the  intrapolar  region. 


fi 

T    ^ 

/ 

\ 

\  ~ 

^ 

-^ 

\y 

Fig.   45. — Diagram  representing  the  contrary  variations  of  excitability  in  the  regions 
adjacent  to  the  negative  and  positive  poles. 

'  NN,  nerve  to  whicli  are  applied  the  two  poles  of  a  constant  battery.  The  two  inverse  varia- 
tions'* are  never  exactly  symmetrical.  When  the  current  is  strong,  there  is  a  tendency  to  the 
invasion  of  the  whole  nerve  by  anelectrotonus.  The  neutral  point  becomes  more  and  more  dis- 
placed towards  the  negative  pole.  When  the  current  is  feeble,  this  displacement  is  made  in  the 
opposite  direction. 


NERVE  ENERGIES 


95 


-According   as   the  current   is 


Spinal  Cord 


A.  medium  current. — In  the  current  which  is  known  as  7nedium, 
this  curve  is  almost  symmetrical  ;  and  the  current  is  called  medium 
by  definition,  when  the  inverse  modifications  of  the  excitability  assume 
this  symmetrical  form.  As  regards  intensities  which  are  superior  or 
inferior  to  that  which  gives  this  result,  the  curve  assumes  shghtly 
different  forms,  which  are  characterized,  not  merely  by  the  stronger 
or  weaker  inflections  towards  the  poles,  but  also  by  the  displacement 
of  the  neutral  or  indifferent  point,  in  one  or  other  direction.  This 
displacement,  which  is  the  greater  in  proportion  as  the  current  is 
stronger  or  weaker,  gives  to  the  curve  that  unsymmetrical  form 
which  has  been  mentioned  above.  In  the  case  of  iveak  currents, 
the  neutral  point  approximates  the  anode,  and  hence  relatively 
increases  the  excitability,  in  one  word,  causes  the  catelectrotonic 
condition  to  predominate  ;  in  the  case  of  strong  currents  the  contrary 
happens  :  the  neutral  point  is  displaced  towards  the  cathode  and 
the  anelectrotonic  condition  predominates,  and  tends  to  occupy  the 
w^hole  nerve. 

Ascending  and  descending  current, 
ascending  or  descending,  these  modi- 
fications are,  in  each  case,  of  opposite 
denomination.  In  the  case  of  the 
ascending  current,  the  area  of  anelec- 
trotonus  affects  the  myopolar  seg- 
ment (that  on  the  side  of  the  muscle)  ; 
in  the  case  of  the  descending  current, 
it  is  the  reverse.  As  the  state  of 
excitability  in  the  nerve  is  rendered 
evident  by  the  contractions  of  the 
muscle,  it  is  obvious  that  these  con- 
tractions will  vary  in  magnitude 
according  to  the  direction  of  the 
current  and  according  to  whether  the 
latter  is  w^eak,  medium,  or  strong,  in 
conformity  with  the  definition  which 
has  been  given  of  these  words  in  the 
particular  case.  It  has  already  been 
pointed  out  that,  in  addition  to  the 
intensity  and  the  direction  of  the 
current,  the  distance  between  the 
excited  point  and  the  polarized 
region  is  also  a  factor  ;  and  regard  must  also  be  paid  to  the  length  of 
the  interpolar  region  and  to  the  duration  of  the  passage  of  the  current. 


?n 


Y 


Ascending 
Current 


Descending 
Current 


Fig.  46. — Diagram  of  experiment  for 
the  study  of  electrotonus. 

N,  battery  connected  with  motor  nerves 
by  two  non-polarizable  electrodes.  Be- 
tween the  two  poles  is  the  interpolar  seg- 
ment ;  below,  the  myopolar  segment  with 
its  muscle  ;  above,  the  centropolar  segment. 

In  the  diagram  on  the  left,  the  cm-rent  is 
ascending  ;  in  that  on  the  right  it  is  de- 
scending. 


96  ELEMENTARY  NERVOUS  FUNCTIONS 

It  is  the  minute  study  of  all  the  circumstances  in  their  multiple  associa- 
tions that  makes  Pfliiger's  work  very  valuable. 

Excitability  and  conductivity. — Excitability  is  the  more  or  less  marked 
aptitude  of  the  nerve  to  receive  locally  the  exciting  impulse  ;  conduc- 
tivity is  the  greater  or  less  aptitude  of  the  nerve  to  transmit  this  im- 
pulse along  its  length  to  the  muscle.  The  modification  of  both  these 
aptitudes  has  one  and  the  same  consequence  :  that  of  increasing  or 
diminishing  the  magnitude  of  the  contractions.  The  analysis  of  special 
cases  proves  that  it  is  now  to  one,  now  to  another  of  these  two  modi- 
fications that  the  change  observed  is  due. 

B.  Strong  current. — Let  it  be  assumed  that  a  strong  or  very  strong 
current  influences  the  middle  region  of  the  nerve,  and  that  this  current 
is  descending,  excitability  will  be  considerably  increased  in  the  area 
approximating  the  negative  pole,  and  consequently  in  the  myopolar 
segment  ;  the  least  excitation  of  this  region  will  provoke  strong  con- 
tractions ;  on  the  other  hand,  excitability  will  be  greatly  reduced  in 
the  centropolar  segment,  and  stimulation  of  this  segment,  especially 
in  the  immediate  neighbourhood  of  the  positive  pole,  will  remain  with- 
out effect.  Here  the  local  excitability  is  increased  on  the  one  side  and 
diminished  on  the  other. 

Let  it  be  supposed,  on  the  other  hand,  that  this  same  current  is 
ascending.  The  catelectrotonic  and  anelectrotonic  areas  are  inverted. 
The  myopolar  segment  is  anelectrotonized,  and  its  stimulation  yields 
no  contraction,  because  its  local  excitability  is  extremely  diminished. 
The  centrapolar  segment  is  catelectrotonized  ;  but,  in  spite  of  the 
local  excitability  of  this  segment  being  augmented,  it  yet  gives  no 
evidence  of  this,  because  the  transmission  of  the  impulse  is  arrested 
in  the  anelectrotonized  myopolar  region.  This  uni vocal  manner  in 
which  excitability  and  conductivity  comport  themselves  with  regard 
to  electrotonus  is  a  strong  argument  in  favour  of  their  identity. 

Anelectrotonus  and  inhibition. — The  stoppage  of  the  contractions  due  to  anelec- 
trotonus  lias  often  been  compared  to  the  result  of  inhibition,  so  much  so,  indeed, 
that  these  two  phenonaena  have  been  completely  assimilated.  If  by  inhibition 
is  implied  every  arrest  due  to  the  intervention  of  some  force,  this  view  is  correct  ; 
but  it  is  necessary  to  remember  that  the  phenomena  usually  described  under 
this  name,  the  stoppage  of  the  heart  by  stimulation  of  the  vagus,  and  a  number 
of  other  more  or  less  analogous  phenonaena,  are  caused,  not  by  a  special  form  of 
action  of  a  stimulus  on  a  nerve,  but  by  the  action  of  the  nerve  on  other  nerves,  an 
action,  further,  which  is  provoked  by  a  trivial  excitation.  If  the  phenomena  of 
inhibition  be  generalized,  it  is  imperatively  necessary  to  define  categories  in  the 
disparate  whole  formed  by  the  facts  which  are  comprised  in  them.  In  the  mean- 
time, there  is  nothing  to  prove  that  the  inhibition  of  one  nerve  by  another  is 
due  to  an  anelectrotonic  action  of  the  terminal  pole  of  the  second  on  tlie  initial 
pole  of  the  first. 


NERVE  ENERGIES 


97 


C.  Weak  Current. — In  proportion  as  the  intensity  of  the  polarizing 
current  decreases,  the  catelectrotonic  action  tends  to  increase  rela- 
tively to  the  converse  action,  and  it  may  predominate  over  it.  Thus 
with  more  feeble  currents  may  be  obtained  contractions  either  with 
the  ascending  or  with  the  descending  current. 

Electrotonus  in  man. — Since  Helmholtz,  a  large  number  of  authors  liave  at- 
tempted to  reproduce  electrotonus  in  man,  but  generally  with  variable,  uncertain 
and  paradoxical  results.  Waller  and  Watteville  have  demonstrated  that  excit- 
ability is  increased  at  the  anode  and  in  the  anodic  region,  while  it  is  diminished 
at  the  cathode  and  in  the  cathodic  region.  In  other  words,  electrotonus  follows 
the  same  rules  in  man  and  in  animals. 

Different  Conditions  mhich  Influence  Electrotonvs. 


Direction  of  the  current 

in  relation 

to  the  physiological  conduction 

of  the  nerve. 

Influence 
of  the  intensity 

of  the 
polarizing  current. 

Initiation 

and 

consecutive 

effects. 

Influence  of 

the  length  of 

intrapolar 

region. 

C. 
J. 

^      in 

H  S 
S  % 

5  S  ■ 
^  R 

c. 

'(Centropolar  seg- 
ment. ) 

Extrapolar   as- 
cending   cai- 
electrotonus. 

The   effect   first 
increases  then 
diminishes 
and  is  invert- 
ed. 

Rapid  initiation ; 
leaving    after 
it    a    positive 
modification, 
preceded  by  a 
short  negative 
phase. 

The    effect   first 
increases  then 
becomes    nil, 
and  is  invert- 
ed. 

o 

o 

(Myopolar      seg- 
ment.) 

Ascending    extra- 
polar       anelec- 
^     trotonus. 

Effect  increases 
progressively 
without 
change  of 
•sign. 

Slow  in'tiation  ; 
maximLim  ob- 
tained   after 
several 
minutes. 

Effect     increases 
without  chang- 
ing sign. 

(Slower  than  for 
intensity. ) 

< 

c. 
J. 


^   ft 


seg- 


( Myopolar 
ment.) 

Descending  extra- 
polar  catelec- 
trotonus. 


(Centropolar  seg- 
ment. ) 

Descending  extra- 
polar  anelec- 
V      trotonus. 


Effect    goes 
increasing. 


Rapid   start, 
slow,  increase; 
leav'es  a  nega- 
tive modifica-  ' 
tion,    then    a  ! 
pos'tive  modi- 
fication, which  j 
disappears.        | 


Effect  grows 
rapidly. 


Effect  increases 
progressively 
without 
change  of 
sign. 


Slow   initiation. 


Effect  increases 
without 
change  of 
sign. 


c 

f 

Z 

c. 

a 

z 

w 

(J 

.T. 

H 

o 

1 

PS 

0 

H 

7, 

Z 

Z 

r 

'O 

V 

The  length  of  the  intrapolar  polarized  region  has  no  effect  on  its 
own  excitability.  The  extension  of  the  modification  is  limited  by 
the  situation  of  the  poles.  The  modification  is  positive  near  one  and 
negative  near  the  otlier.  A  neutral  point  of  unaltered  excitability 
exists  in  the  interval  between  the  poles.  With  the  augmentation  of 
intensity  of  the  current,  this  point  is  displaced  from  the  anode  to- 
wards the  cathode  (consequently  in  the  direction  of  the  current). 
According  to  the  situation  of  this  point  the  total  excitabiUty  of  the 
intrapolar  area  is  augmented  or  diminished.  Whatever  be  the  direc- 
tion of  the  current  (but  especially  ascending)  it  will  be  seen  that  with 
weak  currents  this  total  excitability  is  first  augmented,  Httle  by  little 
attains  a  maximum,  and  is  then  diminished. 

H 


98 


ELEMENTARY  NERVOUS  FUNCTIONS 


3.  Law  of  contraction — In  the  scheme  which  has  just  been  given, 
the  modifying  action  is  supphed  by  a  current  (continuous),  while  the 
exciting  action  is  effected  by  another  current  (induced),  by  means  of 
which  the  different  portions  of  the  nerve  under  examination  are  in- 
vestigated. But  the  battery  current  at  the  instant  that  it  is  directed 
through  the  nerve  produces  an  excitation,  and  when  it  is  broken 
another  excitation  is  brought  about,  in  accordance  with  the  laws 
governing  the  origin  of  the  excitation.  When  a  graduated  series  of 
makings  and  breakings  of  the  continuous  current  is  carried  out  on  a 
nerve,  whether  ascending  or  descending,  a  series  of  excitations  and  of 
modifications  of  excitability  is  all  at  once  initiated  whose  effects 
(muscular  contractions)  are  explained  by  the  law%s  formulated  above. 


Inrifn/j/mt 

Excitab.  diminished 


Fig.   47. — Determination  of  excitability  of  the  myopolar  segment  diu'ing  the  passage 
of  a  current  tlorough  a  certain  length  of  the  nerve. 

In  the  upper  figure,  the  polarizing  current  is  ascending,  excitability  is  diminished  in  the  myo- 
polar segment.  In  the  lower  figure  the  polarizing  current  is  descending,  the  excitability  of  the 
myopolar  segment  is  increased  (after  Waller). 


Diagrammatic   table. — The  results  of  these  series  may  be  systema- 
tized in  the  following  table. 


Current. 


Descending. 


Make. 


Break. 


Ascending. 


Make. 


Break. 


Weak. 

Contraction. 

— 

Contraction. 

— 

Medium. 

Contraction. 

Contraction. 

Contraction. 

Contraction. 

Strong. 

Contraction. 

— 

— 

Contraction. 

Discussion, — As  is  thus  seen,  the  weak  current  causes  two  contractions  at  its 
making,  whether  it  be  descending  or  ascending.  The  medium  current  causes 
four  contractions.     The  strong  current  once  again  brings  about  two,  the  one  at 


NERVE  ENERGIES  99 

the  making  of  the  descending  current,  the  other  at  the  breaking  of  the  ascend- 
ing current.  An  explanation  of  the  absence  of  the  contractions  wliich  are 
missing  must  be  sought  for. 

(a)  Weak  current. — As  regards  weak  currents,  the  two  breaking  contractions 
are  wanting  on  account  of  the  weakness  of  the  cm-rent,  tlie  exciting  action  of  the 
break  being  regarded  as  inferior  to  that  of  the  make,  possibly  in  con3ec|uence  of 
the  alteration  which  is  produced  by  the  passage  of  the  current. 

(b)  Strong  current. — As  regards  the  strong  cm'rent,  the  absence  of  tlie  breaking 
contraction  of  the  ascending  ciurent  is  due  to  the  marked  effect  of  anelectrotonus 
(diminution  of  excitability)  in  the  portion  of  the  nerve  which  is  in  proximity  to 
the  muscle  and  in  contact  with  the  positive  pole.  On  the  other  hand,  the  very 
considerable  magnitude  of  the  breaking  contraction  of  this  same  ascending 
CTorrent  is  due,  after  the  cessation  of  anelectrotonus  in  this  region,  to  a  contrary 
modification,  which  acts  like  catelec  trot  onus  by  augmenting  excitability.  After 
the  cessation  of  the  passage  of  the  current  from  the  battery,  an  after  current  of  opposite 
direction  is  indeed  developed  in  the  nerve  (for  many  reasons,  amongst  others,  elec- 
trolysis), as  in  every  polarized  circuit.  Lastly,  the  absence  of  the  breaking  con- 
traction in  the  case  of  the  descending  current  is  explained  by  the  establislmient 
of  an  after  cvirrent  of  the  same  kind  which,  after  the  cessation  of  catelectrotonus 
developed  by  the  passage  of  the  polarizing  cmrent,  gives  rise  to  the  development 
of  a  contrary  modification  equivalent  to  a  strong  anelectrotonus. 

(c)  Medium  Current. — As  regards  the  medimn  current,  the  exciting  effect  of 
breaking  is  now  sufficient  to  bring  about  an  excitation,  and  on  the  other  hand 
the  anelectrotonic  modifications,  both  direct  and  consecutive,  are  still  SLifificiently 
feeble  not  to  hinder  the  occurrence  of  the  contraction  ;  hence  foiu-  contractions 
— two  on  making  and  two  on  breaking  of  the  two  currents. 

Electrotonic  theory  of  excitation. — On  the  strength  of  these  facts,  Pfliiger 
gives  the  following  formula  of  electric  excitation  :  Excitation  arises  through  the 
production  of  catelectrotonus  or  through  the  cessation  of  anelectrotonus. 

Tetanus  produced  by  the  continuous  current. — When  a  considerable  extent  of 
the  nerve  is  traversed  by  a  continuovis  current  (especially  a  descending  current), 
dm-ing  its  passage  a  continued  contraction — a  tetanic  muscular  contraction — 
may  be  produced. 

Breaking  tetanus. — Conversely,  when  the  ascending  cm'rent  is  strong  and  is 
long  continued,  it  may  produce,  on  breaking,  instead  of  a  shock,  a  tetanic  con- 
traction similar  to  the  preceding.  These  apparently  tetanic  contractions  a^^pear 
to  be  inordinately  prolonged  shocks,  such  as  are  obtained  when  the  nerve  or 
the  mviscle  is  fatigued  or  subjected  to  the  action  of  cold  or  certain  poisons  (vera- 
trine).  Neither  making  nor  breaking  tetanus  (Hering  and  Frederick)  causes 
secondary  tetanus  in  the  galvanoscopic  paw. 

Volta's  alternatives. — For  seen  by  Ritter,  incompletely  formulated  by  Volta, 
the  law  governing  these  phenomena  has  been  expressed  in  the  following  manner 
by  Rosenthal  and  Wimdt  :  The  continued  passage  of  a  current  of  a  given  direction 
increases  the  breaking  excitability  of  the  current  of  the  same  direction  and  the  making 
of  the  current  of  the  opposite  direction  ;  it  weakens  it  as  regards  the  making  of  the 
first  and  the  breaking  of  the  second.  If  the  existence  of  an  after  ciurent  of  polari- 
zation is  admitted,  and  if  the  so-called  breaking  contraction  be  attributed  to 
the  luaking  of  this  inverse  cvurent,  the  law  becomes  simpler  and  may  be  formu- 
lated thus  :  the  passage  through  the  nerve  of  a  current  of  a  given  direction  increases 
the  excitability  of  this  nerve  for  a  current  of  the  opposite  direction. 

Succession  of  effects  with  weak  currents. — According  to  the  authors  who  have 
studied  it,  and  according  to  the  point  of  view  which  each  of  them  has  adopted, 
the  law  of  contraction  assiunes  a  particular  form,  as  is  shown  by  the  tables  which 
have  been  prepared  to  express  it.     Its  mam  outlines  are  sketched  in  Pfiiiger's 


100 


ELEMENTARY  NERVOUS  FUNCTIONS 


table.     That  of  Heidenliain  expresses  in  detail  the  increasing  effects  of  weak 
currents,  until  they  attain  the  intensity  which  is  known  as  medium. 


Current. 

Descending. 

Ascending. 

Intensity.                    Make. 

Break. 

Make. 

Break. 

I.  ...                  — 

II.  ...                  — 

III.  .      .      .         Contraction. 

IV.  ...         Contraction. 

Contraction. 
Contraction. 
Contraction. 

Contraction. 
Contraction. 
Contraction. 
Contraction. 

Contraction. 

Disappearance  of  contractions  as  the  nerve  gradually  perishes. — The  following 
table,  due  to  Nobili,  expresses  the  action  of  another  condition,  that  of  the  varia- 
tion of  excitahility  of  the  cut  nerve  which  belongs  to  a  separated  limb  of  the  animal. 
This  assumes  that  the  stimulations  are  no  longer  extemporaneous,  but  succeed 
one  another  at  long  intervals,  leaving  to  time  the  task  of  performing  its  work. 
The  excitability  of  the  nerve  at  first  progressively  increases  ;  then  it  regularly 
decreases,  and  this  decrease  is  rendered  evident  by  the  gi-adual  disappearance 
of  the  contractions  one  after  the  other.  In  the  case  of  a  nerve  having  its  maxi- 
mum excitability  it  would  be  as  follows  : 


Degree  of 

Descending    Current. 

Ascending  Current. 

Excitability. 

Make. 

Break. 

Make. 

Break. 

I.  ... 

II.  ... 

III.  .      .      . 

IV.  .      .      . 

V.  ... 

Contraction. 

Strong  con- 
traction. 

Strong  con- 
traction. 

Contraction. 

Contraction. 
Weak    con- 
traction. 

Contraction. 

Contraction. 
Strong  con- 
traction. 
Strong  con- 
traction. 

Law  of  Ritter- Valli. — This  table  expresses  the  variations  of  nervous  excit- 
ability regarded  in  their  succession  in  time.  It  should  be  added  that  this  loss  of 
excitability  is  not  total  ;  it  does  not  involve  the  nerve  in  its  entirety,  but  follows 
a  progression  in  the  direction  of  its  length.  In  the  motor  nerve  it  first  affects  the 
extremity  which  is  farthest  removed  from  the  muscle,  and  then  progressively 
involves  the  portions  of  the  nerve  which  are  nearest  to  the  former.  This  mode 
of  disappearance  of  excitability  is  the  same  whatever  may  be  the  nature  of  the 
alteration  which  produces  decay  of  the  nerve  (anaemia,  curare,  CI.  Bernard  ; 
local  anaesthesia,  loteyko  and  Stefanowska).  In  sensory  nerves,  whose  conduc- 
tion is  the  converse  of  that  of  the  motor  nerves,  the  progress  of  the  loss  of  excit- 
ability is  inverted,  and  proceeds  from  the  periphery  to  the  centres.  (The  same 
authors.) 

Electrotonus  in  the  monopolar  applications  of  electricity.  —  A  nerve  may  be 
excited,  as  Chauveau  has  shown,  by  placing  a  single  electrode  of  the  current  on 
it,  while  the  other  electrode  is  placed  on  a  remote  region  (more  or  less  symmet- 
rical). It  hence  follows,  without  any  possible  error,  and  contrary  to  that  which 
Hermann  maintains,  that  electrotonus  (in  other  words,  the  modification  of  excita- 


NERVE  ENERGIES 


101 


ability  which  accompanies  the  electrotonic  currents)  may  and  should  arise  in 
these  conditions  (Morat  and  Toussaint).  Clearly  the  results  of  this  mode  of  a 
unipolar  application  of  electricity  must  be  connected  with  those  of  bipolar  applica- 
tion, and  this  connexion  is  made  manifest  by  arranging,  as  I  have  done,  in  a 
parallel  table  the  results  obtained  by  these  two  methods  of  operating.  A  know- 
ledge of  this  concordance  is  the  more  useful  inasmuch  as  if  bipolar  application 
is  almost  exclusi\-ely  employed  in  physiology,  the  unipolar  method  is  the  only 
possible  and  correct  one  clinically  ;  hence  it  is  necessary  to  make  sure  of  the 
equivalence  of  the  two  methods  in  order  that  clinical  practice  may  benefit  from 
experimental  results. 

From  the  theoretical  point  of  view,  for  the  explanation  of  the  effects  of  elec- 
tricity, this  comparison  is  also  not  without  interest.       It  proves  to  demonstra- 


^ 


Fig.   48. — Progressive  loss  of  excitability  in  tlie  cut  motor  nerve. 

The  iioints    A,  B,  C,  D  become  successively  inexcitable  after  having  undergone  a  slight  phase 
of  hyperexcitabilit\-. 

tion  that  the  specific  nature  of  the  action  for  a  long  time  attributed  to  the 
direction  of  the  current,  really  belongs  to  the  nature  of  the  pole  in  contact  with 
the  stimulated  nerve  (in  the  unipolar  method),  with  the  myopolar  portion  of 
the  nerve  (in  the  bipolar  method).  This  is  markedly  shown  in  the  following 
table,  in  which  the  succession  of  effects  due  to  an  increasing  intensity  of  the 
currents  in  the  two  modes  of  excitation  is  noted. 


Current.               Making. 

Breakixc;. 

Pole. 

Negative 
Positive 

Making. 

Breaking. 

< 

Ascending     Contraction 
Descending            — 

— 

Contraction 

— 

w 
^ 

Ascending     Contraction 
.Descending  Contraction 

— 

Negative 
Positive 

Contraction 
Contraction 

= 

'Ascending     Contraction 
Descending  Contraction 

Contraction 

Negative 
Positi^•e 

Contraction 
Contraction 

Contraction 

Med 

Ascending     Contraction 
Descending  Contraction 

Contraction 
Contraction 

Negative 
Positive 

Contraction 
Contraction 

Contraction 
Contraction 

0 
Iz; 
o 

'Ascending     Contraction 
Descending  Contraction 

Contraction 

Negative 
Positive 

Contraction 
Contraction 

Contraction 

g    ^ 

m 

Ascending              — 
,  Descending  Contraction 

Contraction 

Negative 
Positive 

—            Contraction 
Contraction            — 

Electrotonus  in  nerves  of  different  functions. — Electrotonus,  in  so  far  as  it  is 
a  modification  of  the  excitability,  is  an  absolutely  general  property  of  the  nerves, 
just  as  is  excitability  itself,  or  the  conduction  of  the  impulses,  and  which  mani- 
fests itself,  like  the  latter,  independently  of  the  special  functions  of  these  nerves. 
The  functions  of  nerves  depend  on  their  connexion  with  nervous  or  non-nervous 
elements,  which  they  govern,  or  from  which  they  receive  the  impulse. 


102  ELEMENTARY  NERVOUS  FUNCTIONS 

(a)  Secretory  nerves. — If,  instead  of  a  motor  nerve,  a  secretory  nei've  be  stimu- 
lated, in  i^lace  of  a  nauscular  contraction,  there  will  be  a  flow  of  liquid  from  the 
gland.  The  law  of  contraction  may  be  verified  in  these  new  conditions,  as  Bieder- 
mann  has  shown.  Tliis  author,  operating  on  the  glosspharyngeal  of  the  frog, 
and  the  nerves  of  the  tongvie,  has  found  it  advantageous  to  estimate  by  the 
galvanometer  the  cvirrent  of  secretion,  rather  than  the  secretion  itself. 

(b)  Inhibitory  nerves. — By  stimulating  the  pneumogastric,  wliich  is  the  type 
of  inhibitory  nerves,  by  continuous  currents  of  varied  intensity  and  direction, 
Donders  has  been  able  to  prepare  a  table  of  the  law  of  contractions  similar  to 
that  of  Pfltiger,  except  that  in  it  contraction  is  replaced  by  arrest  of  cardiac 
action,  and  repose  or  want  of  contraction  by  the  continuation  of  the  movement 
of  the  heart. 

(c)  Elements  of  association. — The  inhibitory  nerves  are  not  terminal  neurons, 
like  those  of  the  anterior  roots  proceeding  to  the  muscles  of  the  skeleton  ;  by 
definition  they  are  considered  as  associating  elements  whose  function,  deter- 
mined by  their  special  connexion  with  the  motor  elements  properly  so  called, 
terminates  in  this  apparently  strange  phenomenon,  the  arrest  of  movement. 
The  internal  elements  of  the  nervous  system  (intercentral  elements)  thus  present 
the  phenomenon  of  electrotonvis.  This  is  equivalent  to  saying  that  the  pheno- 
mena of  electrotonus  appertain  to  every  nervous  element. 

Sensory  nerves. — The  initial  nerves,  like  those  which  are  terminal  and  the 
intercentral  nerves,  should  present  electrotonic  modifications.  In  such  nerves, 
and  for  reasons  which  are  readily  understood,  these  phenomena  are  not  easily 
to  be  detected  in  animals,  on  whom  we  can  only  measure  sensibility  under  its 
reflex  form,  and  by  no  means  withoiat  difficulty  (Zurhelle). 

Nerves  of  special  sense — In  man  this  study  has  been  undertaken  on  the  nerves 
of  special  sense. 

(a)  Taste. — The  passage  of  a  cvirrent  through  the  tongue  produces  a  sensation 
of  taste,  acid  at  its  entry,  alkaline  (almost  bitter)  at  its  exit  (Pfaf¥,  Volta  and 
Bitter). 

(b)  Sight. — A  current  proceeding  towards  the  ganglionic  cells  (descending  cur- 
rent) causes  the  sensation  of  darkness  ;  a  curi-ent  proceeding  in  the  opposite 
direction  (ascending  current)  causes  a  sensation  of  light  (Helmholtz). 

(c)  Hearing. — It  may  be  shown,  but  not  without  difficulty,  that  the  law  of 
contraction  is  applicable  also  to  the  sense  of  hearing  (Brenner). 

Polar  influence  on  non-differentiated  protoplasm.  —  Kiihne  was  the  first  to 
demonstrate  the  action  of  electricity  on  the  non-differentiated  or  bvit  slightly 
differentiated  protoplasm  of  the  lowest  animals.  Verworn  has  made  a  method- 
ical study  of  this  action.  It  is  generally  held  that  the  protoplasm  of  the 
unicellular  beings  represents  living  matter  under  an  elementary  form  and 
apart  from  all  the  structures  which  are  superposed  on  it  in  tlie  more  highly 
organized  beings. 

Hence  it  has  been  supposed  that  the  response  of  svich  a  substance  to  excitants 
would  be  equivalent  to  that  of  the  least  differentiated  cells  of  superior  animals, 
and  even  to  that  of  the  least  differentiated  substance  which  exists  in  these  cells  ; 
that,  in  a  word,  it  should  be  univocal  and  very  simple  in  its  expression.  As  a 
matter  of  fact,  the  response  to  electrical  excitations  of  unicellular  beings  is  some- 
what complicated.  This  result  appears  to  indicate  that  the  comparisons  or 
assimilations  made  between  beings  of.  different  organization  are  not  perhaps 
very  accurate.  The  simplicity  of  monocellular  beings  (amcebfe,  infusoria,  etc.) 
is  not  so  great  as  has  been  supposed  and,  above  all,  its  mode  of  expression  is 
otherwise  than  that  which  has  been  held  to  be  the  case.  In  the  amoeba  all  the 
essential  functions  of  life  are  already  represented,  bvit,  in  a  sense,  undivided,  in 
its  protoplasm.     In  tlie  course  of  phylogenetic  evolution,  a  distribution  of  atri- 


NERVE  ENERGIES  103 

butes  is  made  between  the  different  portions  of  this  protoplasm,  a  division  in 
virtue  of  which  each  one  of  them  increases  its  aptitudes  in  a  given  direction,  for 
the  performance  of  a  given  function,  while  it  loses  its  aptitudes  in  an  opposite- 
direction,  to  the  gain  of  other  differentiated  portions  with  regard  to  other  func- 
tions. Hence  evolution,  differentiation,  results  at  the  same  time  in  the  attain- 
ment of  a  greater  perfection  of  the  functions  of  the  whole,  and  in  a  specialization, 
that  is  to  say,  a  reduction  of  the  functions  of  the  part,  hence  the  inability  of  the 
latter  to  live  by  itself  when  it  is  detached  from  the  whole  to  which  it  belongs. 

Galvanotropism. — An  amoeba,  placed  in  a  drop  of  water  through  which  a 
current  is  passed,  reacts  under  the  action  of  this  current.  The  'portion  turned 
toioards  the  anode  (positive  pole)  is  retracted,  ivhile  that  facing  the  cathode  (negative 
pole)  is  protruded  and  forms  a  pseudopodium.  If  the  current  be  reversed,  the 
same  phenomena  occur,  but  in  the  converse  manner.  Hence,  imder  the  action 
of  the  two  opposite  poles,  a  double  inverse  deformation  occurs.  Which  of  the 
two  is  the  equivalent  of  a  muscular  contraction  ?  It  is  very  difficult  to  decide. 
In  a  definite  differentiated  protoplasm,  such  as  that  of  muscle,  nothing  is  more 
clear  than  the  contrary  state  of  repose  and  of  contraction.  But  in  the  diffuse 
protoplasm  of  the  amoeba,  the  direction  of  the  forces  varies  according  to  circxmi- 
stances.  As  a  matter  of  fact,  both  changes  of  form  practically  arise  at  one  and 
the  same  time  from  a  contraction  in  one  direction,  and  a  compensatory  protru- 
sion in  the  other.  Retraction  is  always  the  active  phenomenon.  When  the 
force  is  parallel  to  the  pseudopodium,  it  causes  it  to  retract  ;  when  it  is  circular 
and  perpendicular,  it  causes  it  to  elongate.  In  both  cases  there  is  an  expenditm-e 
of  energy  ;  in  both  cases  there  is  a  contraction,  and  from  a  certain  point  of  view 
the  phenomenon  is  less  simple  in  the  amoeba  than  in  the  muscular  fibre.  That 
which  is  remarkable  is,  that  the  anode  excites  one  of  these  movements  and  the 
cathode  the  other,  in  a  predominant  or  special  manner. 

Yet,  a  double  converse  deformation,  such  as  that  which  has  just  been  de- 
sci-ibed,  implies  a  tendency  to  locomotion.  Certain  unicellular  beings,  ciliated 
or  not,  present,  under  the  influence  of  the  cm-rent,  a  change  of  place  to  which 
the  name  of  galvanotropism  is  more  particularly  applied.  Electrotonus,  the 
reactions  of  excitable  substances  varying  according  to  the  nature  of  the  pole,  or 
the  direction  of  the  current,  are  merely  varieties  of  galvanotropism. 

E.    DIFFERENT  USES  AND  EFFECTS  OF  ELECTRICITY 

Action  of  the  magnetic  field  ;  electric  waves  ;  electric  rays. — When  a  current 
is  projected  into  a  circuit,  lines  of  force  are  developed  around  this  latter  which 
create  around  it  a  field  of  force,  known  as  the  magnetic  field.  If  another  circuit 
is  placed  in  this  field  of  force  (in  an  appropriate  position),  induction  occurs, 
electric  movement  in  this  second  circuit.  If,  instead  of  this  second  circuit,  an 
excitable  tissue  be  placed  in  the  magnetic  field,  as  the  galvanoscopic  frog's  foot, 
what  will  happen  ?  This  qviestion  has  been  studied  by  several  authors,  more 
especially  by  Danielewsky,  and  more  recently  by  Radzikowsky. 

As  a  matter  of  fact,  when  a  frog's  nerve  is  placed  in  a  field  of  force,  it  is  excited 
by  the  variations  of  the  intensity  of  this  field.  In  this  tissue,  the  strvicture  of  which 
is  very  complicated,  it  may  be  admitted  that  induced  currents  are  developed 
which  arouse  to  activity  its  very  excitable  substance.  In  certain  positions  of 
the  nerve  the  stimvilation  is  at  its  maximum,  for  example  in  that  in  which  it  is 
placed  in  the  same  plane  as  the  inducing  circuit  and  i^erpendicular  to  an  element 
of  this  circuit,  the  muscle  being  turned  to  the  outside.  The  arrangement  of  the 
exiDeriment  may  be  greatly  varied,  and  the  nerve  may  be  jilaced  in  the  field  in 
the  neighbourhood  of  one  of  the  isolated  poles  (unipolar  excitation).  The  nerve 
must  be  isolated  ;   if  it  is  left  in  position  surrounded  by  other  tissues,  or  if,  after 


104  ELEMENTARY  NERVOUS  FUNCTIONS 

it  has  been  laid  bare,  it  is  covered  with  a  conducting  envelope,  it  will  no  longer 
be  subjected  to  the  action  of  the  field  of  force.  The  surrounding  tissue  acts  as 
a  shunt  (Radzikowsky)  or,  to  speak  more  precisely,  as  a  screen  (Danilewsky). 

Electric  opacity  and  transparency. — If,  indeed,  some  conducting  body  be  placed 
in  tlie  magnetic  field  so  tliat  it  crosses  the  line  of  progress  of  the  electric  waves 
(a  plate  of  metal,  the  hand),  the  excitation  by  induction  ceases  ;  the  interposi- 
tion of  a  dielectric  (a  glass  plate)  allows  the  waves  to  pass.  The  conductor  is 
opaque  to  the  electric  waves  (as  to  luminous  rays)  ;  the  dielectric,  which  is  often 
known  as  the  isolating  agent,  is  transparent  as  regards  these  rays. 

Electric  immunity. — It  will  thus  be  understood  that  tissues  which  are  but 
little  excitable,  but  which  conduct  electricity,  help  to  render  the  more  excitable 
tissues  irresponsive  to  tlie  action  of  the  magnetic  field,  which  is  created  around 
them  by  the  electric  phenomena  developed  in  the  organism.  In  the  same  way, 
as  regards  an  excitable  cell  or  fibre,  a  conducting  envelope  may  preserve  it  from 
the  excitation  which  would  arise  from  this  cause.  In  order  to  protect  living 
elements  against  stimuli  which  are  not  intended  for  them,  there  would  thus  be 
two  methods  available  :  the  one  consists  in  surrounding  them  with  dielectrics 
which  preserve  them  from  excitation  by  conduction,  the  other  consists  in  sur- 
rounding them  with  conductors  which  prevent  their  being  excited  by  induction. 
The  same  element  may  make  use  of  these  two  methods.  This  special  organiza- 
tion allows  the  element  to  reject  the  excitation  in  certain  of  its  parts,  and  to 
receive  it  in  certain  other  points  of  election. 

High  frequency  currents.  —  The  so-called  high  frequency  currents 
are  those  which  attain  the  number  of  500,000-1,000,000  per  second. 
Their  action  has  been  studied  on  Hving  beings,  partly  by  direct  appli- 
cation, partly  by  placing  the  subject  in  a  solenoid,  which  creates  around 
it  a  field  of  force  (d' Arson val). 

(a)  Direct  action. — The  very  high  frequency  of  these  currents  confers 
a  kind  of  immunity  at  the  site  of  their  passage  on  the  organism  which 
they  traverse.  At  an  equal  voltage,  they  are  infinitely  better  sup- 
ported than  currents  of  an  ordinary  rhythm  (say  100  to  a  second). 
However,  by  augmenting  the  intensity,  they  may  be  rendered  injurious, 
and  death  may  ensue  in  animals  (Bordier  and  Lecomte). 

{h)  Indirect  action  through  a  field  oj  force. — When  an  animal  is  placed 
in  the  interior  of  a  solenoid  in  which  such  currents  circulate,  an  aug- 
mentation of  the  respiratory  exchanges  is  observed  (d' Arson  val).  This 
influence  on  the  exchanges  is  nevertheless  not  due  to  the  special  action 
of  the  induced  currents  acting  on  the  nervous  system,  or  the  tissues, 
but  is  a  secondary  effect  attributable  to  the  heat  developed  by  the 
current.  It  is  known,  indeed,  that  heat  by  itself  increases  the  activity 
of  the  exchanges,  when  it  becomes  increased  to  such  an  extent  that 
the  animal  scarcely  resists  it. 

Death  by  electricity. — Prevost  and  Battelli  have  made  a  special 
study  of  the  mechanism  of  death  by  electricity  and  the  conditions 
which  give  rise  to  it  as  regards  the  electric  agency.  They  have  experi- 
mented on  dogs,  rabbits,  guinea  pigs  and  rats,  by  sending  a  current 


NERVE   ENERGIES  105 

through  the  body  from  the  head  to  the  anus.  The  resistance  of  the 
animal  varied  from  400  to  900  ohms.  The  duration  of  the  apphcation 
varied  from  some  hundredths  of  a  second  to  two  or  three  seconds. 
The  resuhs  differ  according  to  the  animal.  The  authors  have  investi- 
gated the  action  both  of  continuous  and  of  alternating  currents. 

(a)  Alternating  currents. — These  currents  must  be  divided  according 
to  their  tension  into  those  of  low  tension  (10  to  120  volts),  those  of 
medium  tension  (about  620  volts),  and  those  of  high  tension  (1,200  to 
4,800  volts). 

With  currents  of  low  tension  a  stoppage  of  the  heart  u'ith  fihrillary 
tremor  is  observed  in  the  dog.  Respiration  continues  for  some  minutes, 
but  in  its  turn  ceases  by  anaemia  of  the  medulla  oblongata.  The 
animal  dies.  The  rabbit  and  the  rat  offer  a  much  greater  resistance. 
Sometimes  10  volts  will  suffice  to  kill  a  dog. 

Currents  of  medium  tension  produce,  in  the  dog,  a  stoppage  of 
respiration  as  also  of  that  of  the  heart.  In  other  animals  stoppage  of 
respiration  is  usually  alone  observed  ;  further,  there  is  generalized 
tetanus  and  anaesthesia. 

Currents  of  high  tension  cause,  in  all  animals,  stoppage  of  respiration, 
while  the  heart  continues  to  beat.  In  this  case  animals  may  be  saved 
by  the  use  of  artificial  respiration.  But  when,  on  the  other  hand,  the 
heart  stops  first,  artificial  respiration  is  altogether  ineffective. 

(b)  Continuous  current. — These  currents  have  been  raised  up  to  540 
volts.  Although  breaking  is  more  dangerous,  accidents  are  not  ex- 
clusively due  either  to  making  or  to  breaking.  Further,  the  phenomena 
differ  but  little  from  those  which  are  observed  when  alternating  currents 
are  made  use  of. 

Other  things  being  equal  with  regard  to  tension,  when  alternating 
currents  are  made  use  of,  the  number  of  interruptions  to  the  second 
forms  an  important  factor.  This  has  been  made  to  vary  from  9  to 
1,720  to  the  second.  A  rhythm  of  150  the  second  is  that  in  which 
death  is  least  likely  to  occur.  Below,  but  especially  above  this  number, 
the  voltage  must  be  considerably  increased  for  the  same  effects  to  be 
produced.  A  continuous  current  acts  like  an  alternating  current  of 
the  same  voltage  at  350  to  the  second. 

It  is  a  curious  fact  that  the  heart  which  has  been  stopped  by  a  low 
tension  current  may  once  again  be  set  in  action  by  a  high  tension 
current. 

The  results  to  which  these  experiments  lead  are  somewhat  different 
from  those  which  are  generally  accepted. 

Mechanism  of  death, — According  to  the  nature  of  the  animal,  accord- 
ing to  the  voltage  of  the  current,  according  to  its  rhythm  if  it  is  alter- 


106  ELEMENTARY  NERVOUS  FUNCTIONS 

nating,  the  first  stoppage  may  affect  either  respiration  (high  tension), 
or  the  heart  (low  tension).  The  stoppage  of  the  heart  is  clearly  the 
only  cause  of  death,  inasmuch  as  artificial  respiration  is  possible,  and 
the  normal  respiration  may  spontaneously  be  renewed,  which  does 
not  occur  in  the  case  of  the  heart. 

Currents  of  medium  and  low  tension  should  then  be  more  dangerous 
than  those  of  high  tension.  As  a  matter  of  fact,  when  death  ensues 
it  is  always  by  stoppage  of  the  heart.  Artificial  respiration  should, 
nevertheless,  be  attempted  and  persevered  in. 

The  observations  which  have  been  made  in  cases  of  death  from 
accidents  arising  in  the  industrial  applications  of  high  tension  elec- 
tricity must  be  regarded  as  being  contradictory  ;  the  tension  of  the 
current  to  which  the  victim  has  been  subjected,  by  derivation  or  other- 
wise, not  usually  being  that  of  the  direct  current  which  circulates  in 
the  line,  but  usually  much  weaker,  its  exact  strength  being  indeter- 
minate. 


F.     NERVE    POISONS 

CI.  Bernard  was  the  first  to  analyse  the  tissues  and  their  func- 
tions by  means  of  poisons,  which  for  this  reason  he  called  the  "  reactives 
of  the  physiologist."  In  this  order  of  investigation  he  has  left  examples 
and  methods  which  his  successors  can  only  imitate  and  make  use  of 
without  essentially  perfecting  them.  He  divides  j)oisons  into  general 
and  special,  according  as  their  action  affects  every  cell,  or  only  certain 
species  of  cells  ;  or,  further,  certain  varieties  of  cells,  as  happens  in 
the  case  of  the  nervous  system. 

1.  General  poisons — Anesthetics.  —  CI.  Bernard  regarded  anaes- 
thetic substances  as  general  poisons,  capable  of  suspending  (without 
destroying,  when  their  action  is  not  indefinitely  prolonged)  the  activity 
of  all  cellular  protoplasm.  They  are  for  him  the  reactives  of  life.  The 
germination  of  cereals,  the  growth  of  plants,  the  movements  of  the 
sensitive  plant,  are  arrested  by  the  vapours  of  chloroform  or  of  ether, 
as  is  sensation  in  animals.  In  these  latter,  the  movement  of  the  vibra- 
tile  cilia,  the  contraction  of  the  muscles,  the  excitability  of  the  motor 
nerves,  in  a  word,  that  of  all  the  tissues,  may  be  paralysed  if  the  tension 
of  the  vapours  is  sufficient  and  their  action  sufficiently  prolonged. 
But  it  must  also  be  added  that,  between  the  different  species  of  cells 
and  between  the  different  systematizations  which  may  be  effected  by 
them,  there  are  well  defined  susceptibilities  and  fairly  large  gradations, 
from  which  it  results  that  in  limiting  precisely  the  doses  (tension  of 
the  vapours)   these  systems  and  these  elements  may  be  attacked  one 


NERVE  ENERGIES  107 

after  the  other  ;  hence  arises  another  form  of  physiological  analysis 
carried  out  by  the  aid  of  poisons. 

The  anaesthesia  of  chloroform  and  ether. — The  action  of  anaesthetics 
(chloroform  and  ether  being  especially  considered)  may  be  divided 
into  three  periods,  up  to  the  instant  when  insensibility  is  complete. 

The  first  period  is  characterized  by  a  sort  of  drunkenness  which,  in 
more  than  one  point,  resembles  alcoholic  drunkenness  :  vertigo,  loss 
of  equilibrium,  stimulation  of  the  different  senses  and  of  cerebral 
activity,  general  excitement.  This  is  the  so-called  period  of  excita- 
tion, which  is  never  completely  wanting,  and  which  should  not  be  con- 
founded with  a  purely  local  irritation  of  the  anaesthetic  vapours  on 
the  upper  respiratory  tract.  The  sensations,  which  are  at  first  exalted, 
are  afterwards  dulled  and,  before  consciousness  is  lost,  a  condition  is 
manifested  of  fleeting  duration  and  difficult  to  obtain  and  voluntarily 
maintain,  which  is  yet  not  anaesthesia,  but  analgesia,  and  during  which 
painful  sensations  are  alone  suppressed. 

The  second  period  corresponds  to  a  true  condition  of  anaesthesia 
characterized  by  insensibility  to  ordinary  painful  impressions,  as  well 
as  those  which  are  not  painful,  but  in  which  reflex  excitahility  is  entirely 
preserved,  if  not  increased.  The  anaesthetic  action  should  be  carried 
slightly  farther  in  order  to  ensure  the  muscular  flaccidity  which  is 
favourable  to  operation  and  to  the  manoeuvres  of  surgery. 

In  the  third  period,  that  of  complete  anaesthesia,  the  reflexes  of  the 
life  of  relation  disappear,  especially  the  winking  of  the  eyelids  con- 
secutively to  touching  of  the  cornea,  the  patellar  reflex,  the  labio- 
mental reflex  (Dastre  and  Loge).  The  muscles  of  the  limbs  are  relaxed. 
The  respiratory  reflexes,  all  those  which  maintain  the  acts  of  the  life 
of  nutrition  and  whose  sphere  lies  in  the  internal  organs,  are  preserved. 
Not  that  these  functions  do  not  receive  the  rebound  of  the  toxic  action 
which  gradually  attacks  the  nervous  system,  as  is  evident  by  the  modi- 
fications of  the  circulation  and  of  the  temperature,  but  the  more  simple 
and  more  resisting  sj^stems  which  govern  them  preserve  their  united 
action  to  a  sufficient  degree. 

Anaesthetic  syncope. — If  the  intoxication  is  puslied  farther,  a  serious  plieno- 
nienon  gradually  supervenes,  menacing  life  ;  this  is  respiratory  syncope,  the  stop- 
page of  the  movement  of  respiration  which  may  be  combated  by  the  emploj'ment 
of  passive  respiration  artificially  maintained  by  the  aid  of  movements  of  the 
thorax.  In  chloroform  anaesthesia  cardiac  syncope  may  occur  suddenly,  and 
is  almost  hopeless  ;  further,  this  accident  may  occur  at  the  very  commencement 
of  anaesthesia.  In  animals,  of  which  some,  like  the  dog,  are  liable  to  this  com- 
plication, it  may  be  prevented  by  the  previous  injection  of  a  small  dose  (half 
milligramme)  of  sulphate  of  atrojiine,  which  diminishes  the  inhibitory  action  of 
the  vagus  on  the  heart  (Dastre  and  Morat).     This  method  may  be  combined  with 


108  ELEMENTARY  NERVOUS  FUNCTIONS 

that  of  CI.  Bernard,  who  administers  morphine  to  the  animal  previously  to  its 
being  ansesthetized. 

During  complete  anaesthesia,  the  pupil  remains  contracted  even  when  the 
eyelids  are  closed.  At  the  instant  when  respiratory  asphyxia  occurs  it  abruptly 
dilates.  The  state  of  the  pupil  should  be  watched  so  long  as  anaesthesia  is 
maintained. 

Cocaine. — Cocaine  may  be  classed  amongst  the  general  poisons  of  the  nervous 
system  in  almost  the  same  category  as  the  anaesthetics.  Employed  in  watery 
solution,  wherever  it  comes  in  contact  with  nerve  protoplasm,  it  suspends  or 
destroys  its  excitability.  Sensory  nerves,  motor  nerves,  white  and  grey 
matter,  all  are  subjected  to  its  paralysing  influence.  It  is  employed  locally 
(clinicalljO  in  order  to  extinguish  for  a  time  the  sensibility  of  certain  surfaces, 
such  as  those  of  the  larynx  or  the  cornea. 

Cocaine  has  been  regarded  in  turn  by  some  (Laborde,  Arloing,  I>affont)  as  a 
special  poison,  a  sensor;/  curare  ;  by  others  (U.  INIosso,  Danilewsky,  Charpentier) 
as  a  general  poison,  a  genuine  ancesthetic.  The  first  of  these  two  opinions  is 
based  on  the  local  anaesthetic  effect,  easily  obtained  by  painting  mucous  mem- 
branes or  the  skin  with  a  solution  of  cocaine,  while  the  excitation  of  sensory 
nerves  which  leave  these  localities,  proves  them  to  be  very  sensitive  ;  the  ulti- 
mate ramifications  would  thus  alone  be  affected  and  not  the  nerve  trunks,  or 
the  cerebral  centres.  The  conclusion  is  not  accurate.  It  is  known,  through 
the  example  of  atropine,  that  an  action  which  is  purely  local  as  regards  the  pupil 
after  installation  into  the  eye  does  not  exclude  the  general  action  of  the  sanae 
substance  diffused  in  the  blood,  even  in  a  mininium  dose.  The  comparison  of 
the  relative  weight  of  the  substance  employed  on  the  one  hand  and  of  the  re- 
acting tissue  on  the  other  hand,  proves,  on  the  contrary  (for  both  poisons)  that 
local  action  is  only  produced  by  large  doses,  while  the  general  action  is  obtained 
by  doses  which  are  comparatively  verj-  small  (say  2  milligrammes  per  kilogramme 
in  the  dog). 

The  opinion  that  the  substance  injected  into  the  blood  would  only  affect  the 
peripheral  ramifications  of  sensory  nerves  cannot  be  maintained.  A  nerve  trunk 
being  isolated,  it  may  be  subjected  locally  to  the  action  of  cocaine  ;  it  then  loses 
at  this  point  its  excitability  and  its  conductivity.  The  excitations  made  above 
the  point  operated  on  are  no  longer  transmitted  to  the  terminal  sensory  or  motor 
organs.  This  effect  at  once  vanishes  with  the  elimination  of  the  substance.  In 
this  manner  a  delicate  means  of  replacing  the  section  of  the  nerves  is  available, 
and  it  allows  also  the  complete  return  of  function  (two  to  four  drops  of  the  one 
per  cent,  solution  injected  under  the  sheath  of  the  vagus  are  sufficient  to  paralyse 
it). 

The  action  of  cocaine  thus  ap23lies  to  all  varieties  of  nerve  protoplasm  (sensory, 
motor,  voluntary,  involuntary  nerves,  etc.).  It  also  applies  to  the  protoplasm 
of  the  muscle.  When  the  substance  is  brought  in  contact  with  the  muscles,  it 
modifies  their  power  of  contracting  (Sighicelli,  U.  Mosso).  The  anaesthetic 
effect,  in  the  general  sense  of  the  expression,  is  displayed  in  all  the  branches, 
whether  they  have  or  have  not  a  nervous  system  (Danilewsky).  It  hinders  the 
diapedesis  of  the  white  corpuscles,  without  however  suspending  the  chemiotaxis, 
as  does  chloroform  (Massart  and  Bordet).  It  stops  fermentation  and  germina- 
tion (A.  Charpentier). 

Thus,  therefore,  the  action  is  a  very  general  one  as  concerns  all  protoplasm, 
but  it  is  an  action  wliich  varies  unequally  according  to  the  nature  of  the  element 
of  the  tis.sue  ;  it  must  be  added  also,  that  it  is  an  action  which  varies  according 
to  the  doses  employed  (stimulating  in  a  weak  dose,  paralysing  in  a  strong  dose). 
When  diffused  in  the  organism,  cocaine  gives  rise  to  somewhat  complicated 
effects,  like  all  anaesthetics,  but  which,  on  account  of  their  special  nature,  make 


NERVE  ENERGIES  109 

this  substance  inapplicable  as  an  ordinary  anesthetic,  such  as  is  employed  surgi- 
cally. Hence  it  has  been  reserved  for  local  application,  especially  for  superficial 
application,  so  that  there  is  no  danger  of  marked  absorption  of  this  sulastance 
causing  genex'al  effects. 

It  has  been  shown  experimentally  that  cocaine  acts  on  the  grey  masses  of  the 
nervous  system  in  the  same  way  as  it  acts  on  its  terminations  or  its  conductors. 
When  applied  directly  to  the  cerebral  cortex  (motor  area),  it  diminislies  its 
excitabilitj-  (Charpentier,  Carvallo)  ;  when  injected  into  a  segment  of  the  sj^inal 
cord,  it  diminishes  its  reflex  power  (U.  Mosso).  Gaglio  has  made  use  of  it  in 
order  to  study  the  functions  of  the  semi-circular  canals. 

When  injected  into  the  general  circulation,  it  first  attacks  the  higher  functions 
of  the  nervous  system,  and  more  especially  sensation,  but  it  does  not  produce 
the  dissociation,  at  the  same  time  regular,  prompt  and  gradual,  which  gives  their 
therapeutic  value  to  ether,  chloroform  and  nitrous  oxide.  TheoreticaUy  it  is  an 
anaesthetic,  but  not  practically  (Dastre). 

2.  Special  Poisons. — Specificity  must  not  probabty  be  taken  in  the 
absolute  sense  of  the  word.  But  it  may  be  admitted  when  it  is  appHed 
to  the  action  of  agents  which  in  infinitesimal  doses  paralyse  certain 
elements,  while  in  a  large  dose  they  leave  the  properties  of  others 
intact.  This  is  the  case  with  curare  and  with  a  certain  number  of 
substances  whose  effects  are  similar  or  analogous. 

Curare. — Curare  is  employed  in  an  aqueous  solution  of  y^rr  strength 
injected  usually  under  the  skin  or  into  the  veins.  According  to  its 
equality,  its  toxicity  varies.  Curare  of  good  quality  produces  its 
ordinary  effects  in  one  centigramme  doses  (one  cubic  centimeter  of 
the  solution  of  1  in  100)  to  the  kilogramme  of  animal  injected  hypoder- 
mically  ;  when  injected  into  a  vein,  the  dose  may  be  diminished  by 
half.  In  an  ordinary-sized  frog,  two  to  four  drops  suffice,  injected 
hypodermic  ally . 

Curare  paralyses  the  motor  nerves  to  the  exclusion  of  the  other  elements  of  the 
nervous  system  and  of  those  of  the  other  tissues.  An  animal  intoxicated  by 
ciu-are  becomes  paralysed.  If  the  excitability  of  the  nerves  and  of  the  muscles 
is  immediately  investigated,  it  is  seen  that  these  last  respond  freely  to  the  electric 
stimulus,  while  the  stimulation  of  the  motor  nerves  is  without  effect. 

Intoxication  by  curare  is  effected  at  the  terminal  extremity  of  the  nerve  ;  in  the 
new  phraseology,  by  the  distributing  pole  of  the  motor  nexu'on.  This  may  be 
proved  by  the  following  experiment  :  a  frog  is  taken  and  a  ligature  is  tightly 
tied  round  the  loins  ;  thus  all  conxmunication  is  prevented  by  the  vessels  between 
the  anterior  and  the  posterior  portion  of  the  body,  but  the  lumbar  nerves  are 
left  outside  the  ligature,  and  are  thus  respected.  When  curare  is  injected  into 
the  anterior  portion,  the  anterior  members  and  the  head  are  incapable  of  move- 
ment ;  the  posterior  members  on  the  contrary  are  not  jaaralysed,  and  this  in 
spite  of  the  fact  that  the  origins  of  their  motor  nerves  and  the  spinal  cord  itself 
are  bathed  in  the  poison  which  is  diffused  through  all  the  parts  situated  in  front 
of  the  ligatm-e.  If  the  frog  is  thrown  into  water,  it  swims  with  its  posterior 
limbs  until  it  reaches  the  edge  of  the  vessel. 

In  intoxication  by  curare  the  sensory  nerves  are  respected.     If  in  the  frog  thus 


110  ELEMENTARY  NERVOUS  FUNCTIONS 

prepared  one  of  the  antei'ior  feet,  paralysed  as  regards  movement,  is  pinched, 
the  animal  reacts  by  movements  of  its  posterior  limbs. 

In  intoxication  by  curare  a  distinction  is  fnade  between  nerves  of  animal  life  and 
those  of  organic  life.  If  intoxication  is  effected  with  a  very  small  dose,  the  motor 
nerves  of  the  skeleton  are  alone  paralysed,  the  nerves  of  organic  life  remain 
active  ;  the  pupil  dilates  and  contracts,  as  also  the  vessels,  the  stomach,  the 
intestine,  etc.  But  if  the  dose  be  increased,  these  nerves  in  their  turn  will  be 
paralysed.  The  intrinsic  nerves  of  the  heart  resist  the  longest  and,  in  cold- 
blooded animals,  the  heart  preserves  its  movements  even  when  large  doses  are 
given. 

Struck  by  the  fact  that  the  paralysis  of  the  motor  nerves  is  only  produced  in 
proportion  as  ciu-are  is  administered  by  its  muscular  ending,  Vulpian  concluded 
that  this  substance  acts  locally  and  in  an  elective  fashion  on  the  terminal  plate 
of  the  motor  nerve,  the  rest  of  the  nerve  preserving  its  properties,  but  without 
the  possibility  of  manifesting  them,  on  account  of  its  temporary  separation 
from  the  muscle.  Against  this  view  CI.  Bernard  cited  the  following  fact,  the 
knowledge  of  which  is  due  to  him,  as  that  of  all  the  preceding  facts.  If,  during 
the  time  that  the  intoxication  is  in  progress,  the  excitability  of  the  different  portions 
of  the  nerves  be  investigated,  it  is  seen  that  the  latter  disappears,  not  totally  and 
at  once,  but  gradually  and  successively  from  the  spinal  cord  to  the  muscle. 
There  is  a  kind  of  paradox  in  the  fact  that  the  paralysis  commences  in  the  ex- 
tremity opposed  to  that  by  which  the  poison  is  supposed  to  enter  into  contact 
with  the  nerve  in  order  to  affect  the  latter. 

A.  D.  Waller  remarks  that  the  different  varieties  of  curare  are  not  identical. 
Having  experimented  with  curarine  chemically  isolated  from  curare,  he  finds 
that  this  substance  produces  motor  paralysis  like  curare,  but  permits  the  nega- 
tive variation  of  the  motor  nerve  to  persist.  Tlius  motor  paralysis  would  be 
due  to  a  functional  dissociation  of  the  nerve  and  of  the  muscle,  according  to  the 
hypothesis  of  Vulpian.  The  anaesthetics  or  general  poisons,  on  the  contrary, 
attack  the  nerve  protoplasm  and  suppress  the  negative  variation,  in  other  words, 
the  special  activity  of  this  protoplasm. 

Strychnine. — At  the  first  glance  strychnine  produces  effects  exactly  the  con- 
verse to  those  of  curare.  Poisoning  by  strychnine  is  rendered  evident  by  con- 
vulsive attacks,  to  which  the  most  trifling  stimulation  of  the  extremities  of  the 
sensory  nerves  gives  rise.  This  fact  is  expressed  by  saying  that  this  substance 
increases  the  reflex  excitability  of  the  spincd  cord.  When  the  convulsive  attacks 
are  violently  repeated  a  certain  munber  of  times,  the  motor  nerves  themselves 
become  inexcitable  ;  this  may  be  partially  due  to  the  fatigue  of  the  system  which 
results  from  over-stimulation.  Martin-Magron  and  Vulpian  have  nevertheless 
observed  that,  when  given  in  large  doses,  strychnine  destroys  the  excitability 
of  the  motor  nerves,  even  if  the  latter  liad  l^een  previously  separated  from  the 
spinal  cord.  This  is  a  fact  which  must  be  reckoned  with,  but  it  is  not  of  a  nature 
to  explain  the  convulsions  at  the  commencement  and  which  are  produced  by 
doses  far  from  large,  and  which  is  the  striking  fact.  Knowing,  as  will  be  ex- 
plained further  on,  that  the  spinal  cord  contains  both  motor  and  inhibitory 
elements  as  regards  movement,  it  is  easily  understood  that  naeduUary  hyper- 
excitability  is  the  result  of  a  paralysing  action,  if  this  paralysis  affects  unequally 
the  two  species  of  elements,  the  inhibitory  tnore  than  the  motor.  On  the  other  hand, 
it  is  possible  to  explain  how  moderate  closes  of  strychnine  paralyse  the  motor 
nerves  of  the  skeleton  without  convulsion,  when  these  nerves  are  separated  from 
the  cord,  as  they  do  not  contain,  like  tlie  latter,  inhibitory  elements. 

Strychnine  would  thus  be  indeed  a  cixrare,  but  one  affecting  preferably  the 
inhibitory  nerves  of  the  animal  nervous  system,  which  are  hidden  away  in  the 
interior  of  the  vertebral  column,  in  the  cord  and  the  superior  centres. 


NERVE  ENERGIES  111 

One  milligramme  of  hydrochloride  of  strychnine  suffices  to  kill  an  adult  rabbit  ; 
2|  niilligrammes  to  3  milligi-ammes  will  kill  a  moderate-sized  dog  ;  1  centigramme 
hypodermically,  2  centigrammes  taken  by  the  mouth,  will  jjlace  the  life  of  man 
in  danger  (Vulpian).  Upas-antiar  has  an  action  closely  analogous  to  that  of 
strychnine,  at  least  as  regards  certain  of  its  effects  (Doyon). 

Belladonna,  Atropine. — Atropine,  like  the  substances  which  are  still  to  be 
mentioned,  has  an  elective  action  on  the  vegetative  nervous  system,  and  more 
particularly  on  certain  of  its  nerves. — As  regards  the  secretory  nerves,  especiallj^ 
the  nerves  of  sudation  and  of  salivation,  it  acts  like  curare,  by  destroying  their 
excitability,  and  consequently  by  preventing  the  secretion  of  these  glands. 
As  regards  the  nerves  of  the  heart,  it  selects  their  inhibitory  elements  ;  it  causes 
a  sort  of  convulsion  of  the  heart,  by  hastening  its  beats.  In  this  case,  as  the 
inhibitory  cardiac  nerves  (by  the  pneumogastric)  extend  away  from  the  vertebral 
column  and  are  distinct  from  its  motor  nerves  (contained  in  the  great  sym- 
pathetic), it  has  been  possible  to  prove  directly  that  atropine  naakes  them 
inexcitable. 

A  half  milligi'amme  of  suljihate  of  atropine,  injected  hypodermically,  suffices, 
in  man,  to  demonstrate  the  effect  of  the  poison  through  a  diminution  of  the 
saliva  and  sweat  secretion  and  a  very  slight  acceleration  of  the  heart.  Substitu- 
tutes  for  atro]iine  are  hyosciamine,  daturine,  duhoisine. 

Jaborandi,  Pilocarpine. — The  effects  of  pilocarpine  are  apparently  the  exact 
reverse  of  those  of  the  preceding  substance.  It  paralyses  the  accelerators  of  the 
heart  (consequently  slowing  its  beats,  which  atropine  hastens)  ;  it  convulses  the 
sudoriparous  and  salivary  glands,  whose  inhibitory  elements,  it  must  be  allowed, 
are  paralysed.  This  antagonism  is  indeed  reversible  or,  as  is  still  said,  bilateral, 
in  this  sense  that,  by  the  alternative  and  superposed  actions  of  the  two  poisons, 
it  is  possible  to  invert  the  effects  a  certain  number  of  times  (provided  that  a 
certain  dose  is  not  exceeded).  The  antagonism  is  not  between  the  two  substances 
which  chemically  neutralize  each  other,  but  between  the  systems  of  nerves  {motor  and 
inhibitory)  which  oppose  one  another  in  their  function,  and  which  the  substances 
attack  eleetively,  the  one  preferably  to  the  other,  according  to  circmiistances. 
Substitutes  for  pilocarpine  are  eserine  and  muscarine. 

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application  a  la  determination  de  la  vitesse  des  licjuides  dans  les  organes  de  cette  plante, 
C.  R.  Acad,  sc,  1879  ;  Influence  des  feuilles  envisagees  coninie  cavise  de  la  circulation 
des  lic^uides  nutritifs,  Soc.  agricult.,  Lyon,  1883. — Cl.  Bernard,  Legons  sur  les  anes- 
thesiques  et  I'asphyxie,  Paris,  1875. — Budin  et  Coyne,  Etat  de  la  pupille,  Biol.,  1875  ; 
Arch,  de  phys. — Dastre,  Les  anesthesiques,  physiologie  et  applications  chirurgicales, 
Paris,  1890  ;  Revue  sc  med.,  art.  "  Chloral,"  1881. — R.  Dubois.  Anesthesie  physiologique 
et  ses  applications,  Paris,  1894. — Flourens,  C.  R.  Acad,  sc.,1851. — Joteyko  et  Stefan- 
owska,  Anesth.  gen.  et  anesth.  locale,  C.  R.  Acad,  sc,  1889  ;  Biol.,  1902. — Richet,  Art. 


NERVE  ENERGIES  113 

"Anesthesie"    dans   Dictionnaire,  index  bibliographique. — Soulier,  Traite  de  thera- 
peutique. — Vulpiak,     C.  R.  Acad,  sc,  1878. 

Cocaine. — Albertoni,  Protoplasma,  Arch.  ital.  de  biol.,  1891. — Von  Anrep,  Arch, 
de  Pfliiger,  1880,  p.  38. — Belmondo,  Ecorce  cerebrale,  Lo  Sperimentale,  1891. — Dastre, 
Bevue  sc.  med.,  1892. — -Ferreira  da  Silva,  Reaction  .   .   .,Journ.  de  pharm.  etde  chim., 

XII. — Fran(.ois-Franck,  Techn.  exper..  Arch,  de  phys.,  1892. — Gley,  Biol.,  1891. 

Mosso,  Arch.  ital.  de  fetoL,1891. 

Curare. — Cl.  Bernard,  Physiologie  experimentale  ;  snbst.  toxiq.  et  medic.  ;  science 
experimentale. — Bezold,  Arch.  Beich.  et  du  Bois-Beymond,  1860. — Bochefontaine 
et  Tiryakan,  Conine  .  .  .,  C.  B.  Acad,  sc,  1878. — Boehm,  Chemisch.  Stud.,  Beitrag. 
z.  Phys.  Carl  Ludvng.  Festschr.,  1887  ;  Arch,  de  Pfliiger,  1875  et  1894  ;  Arch,  de  pharm., 
1897. — Gouty,  Act.  convulsi\^,  C.  B.  Acad,  sc,  1882. — Ciu-are  et  strych..  Ibid.,  1882. — 
CouTY  et  Lacerda,  Excit.  muscul.  du  debut  .  .  .,  Biol.,  1880  ;  Le  curare,  son  origine 
son  action,  ses  usages.  Arch,  de  phys.,  1880. — Dastre,  Action  du  curare,  Biol.,  1884. — 
JoLYET  et  Pelissard,  Biol.,  1868. — Joteko,  Curare  et  poisons  curarisants.  Diet,  de 
phys.,  index  bibliogr. — Hermann,  Bevue  sc.  med.,  1879,  t.  XIV. — Kolliker,  Arch.  f. 
Anat.  und  Phys.,  1856. — W.  Mitchell,  Journ.  de  la  phys.,  1862. — A.  Moreau,  C.  B. 
Acad,  sc,  1860. — Pelikan,  Bull.  Acad,  sc,  Saint-Petersbourg,  1857,  t.  III. — Pollitzer, 
Journ.  of  Phys.,  1886. — Schiff,  Ges.  Beitr.  z.  Phys.  1896. — Tarchanoff,  Arch.de  phys., 
1875. — VoisiN  et  Liouville,  Journ.  d'anat.  et  de  physioL,  1867. — Vulpian,  Ai-ch.  de 
jihys.,  1876  ;    Lemons  sur  les  svibst.  toxicjues. 

Strychnine. — Cl.  Bernard,  Subst.  toxiq.  et  medicamenteuses. — Couty,  C.  B.  Acad, 
sc,  1883. — Delaunoy,  C.  B.  Acad,  sc,  1881. — Delezenne,  Act.  vaso-dilat.,  Arch,  de 
phys..  1894. — M.  Doyon,  Upas  antiar,  Arch,  de  phys.,  1882. — E.  Heckel,  Bevue  scient., 
1879. — Magendie,  C.  B.  Acad,  sc,  memoire,  1809. — Martin-Magron  et  BuissoN, 
Strych.  et  cxirare,  Journ.  de  Br.-Seq.,  t.  II,  III  et  IV. — Th.  Mays,  Brucine  et  strychnine, 
Journ.  of  Phys.,  1887. — A.  Moreau,  Biol.,  1865. — Ch.  Richet,  C.  B.  Acad,  s'c,  1880, 
t.  XCI,  p.  131. — ScHiFF,  Infl.  pupille.  Arch,  de  Pfliiger,  1871. — Stannius,  Mailer's  Arch., 
1837,  p.  223. — Verworn,  Arch.  f.  Anat.  und  Phys.,  1900. — Vulpian,  Arch,  de  phys., 
1870  ;  C.  B.  Acad,  sc,  1882,  t.  XCIV,  p.  555  :  Lemons  svu*  subst.  toxiq.  et  medicament., 
Paris,  O.  Doin,  1882. 

Atropine. — Heidenhain,  Arch,  de  Pfliiger,  1872. — Iveuchel,  Tliese  Dorpat,  1868. — 
A.  Marcacci,  Cinchonamine  .  .  .,  Arch.  ital.  de  biol.,  1888. — A.  Meuriot,  These  Paris, 
1868  (bibhographie). — Nuel,  Art.  (Atropine)  Diet,  de  phys.,  index  bibhogr. — Schmiede- 
BERG,  Ber.  d.  Sach.  Gesell.  f.  Wiss.,  1870. — Schiff,  Moleschotfs  Unters.,  1865. 

Jaborandi. — Pilocarpine. — Gysi,  These  Berne,  1879. — Hardy,  Bevue  sc.  med.,  t.  XI, 
1878,  p.  767. — Langley,  Stud.  fr.  the  Phys.  Labor.,  Univers.  Cambridge,  1877. — Ortille, 
Bull,  therap.,  1879. — Oulmont  et  Laurent,  Hyosc.  et  datur..  Arch,  phys.,  1870. — 
PiLiciER,  These  Berne,  1875. — P1T013,  These  Paris,  1879,  No.  162.— Rabuteau,  U7iion 
medicale,  1874. — Robillard,  These  de  Lille,  1881. — A.  Robin,  Etud.  physiol.  et  therap. 
sur  jabor.,  Paris,  Masson. — Vulpian,  Lemons  sur  les  subst.  tox.  et  medicam. 

Antagonism. — J.-N.  Langley,  Brit.  med.  Journ.,  1875  :  Journ.  of  Anat.  and  Phys., 
1880-1882. — LucHSiNGER,  Arch,  de  Pfliiger,  1877  et  suiv. — Morat,  Bevue  scient.,  1892  ; 
Diet,  de  phys.,  art.  "  Antagonisme." — Is.  Ott,  Muscar.  et  atrop.,  Journ.  of  Phys.,  1878- 
1879. — Prevost,  Arch,  de  phys.,  1877,  et  C.  B.  Acad,  sc — Rossbach,  Arch,  de  Pfluger, 
1875. — Sydney  Ringer  and  Mokshead,  Atrop.  piloc,  Journ.  of  Phys.,  1879-1880. — 
Schmiedeberg,  Elem.  de  pharmacodyn.,  trad,  franc,  1893. — Sticker,  Centralol.  f 
Jclin.  Med.,  1892. 

Anaemia. — Cl.  Bernard,  Rapport  sur  la  physiologie,  1867. — Richet,  Les  nerfs  et 
les  muscles. — Stefani  et  Cavazzani,  Arch.  ital.  de  biol.,  1888,  t.  X,  p.  202. 


FART   II 

Systematic    Functions 

The  functions  known  as  systematic  differ  from  cellular  functions  as 
the  whole  differs  from  the  part  ;  they  are  the  functions  ichich  originate 
in  the  associations  and  definite  relationships  which  are  established  between 
the  cellular  functions,  just  as  the  systems  which  thej^  sustain  arise  them- 
selves from  the  associations  and  relationships  effected  between  their 
component  cells.  These  functions  and  these  systems  form,  the  first 
from  the  dynamic  point  of  view,  the  second  from  the  static,  perfectly 
coherent  aggregations  ;  the  animal  organism  itself  is  nothing  more 
than  an  aggregation  of  this  description  whose  nervous  system  helps  to 
consolidate  all  the  separate  portions.  By  analysis  this  organism  may 
be  resolved  into  aggregations  of  the  same  nature,  genuine  partial 
systems,  of  which  the  surfaces  of  separation  are  continued  into  the 
nervous  system  in  different  directions.  The  definition  of  their  fre- 
quently changing  hmits,  their  specific  functions,  their  mutual  relation- 
ships, is  the  end  which  it  is  the  object  of  the  study  of  the  nervous 
system,  regarded  as  a  system,  to  attain  ;  an  end,  in  the  present  state 
of  knowledge,  still  very  imperfectly  realized. 

The  conception  of  the  system.  — A  system  is  a  whole  composed  of  parts  liaving 
a  determinate  imion  amongst  theniselves  whicli  gives  to  the  whole,  that  is  to  say 
to  the  system,  its  cohesion,  its  existence.  A  system  is  at  the  same  time  both 
a  unity  and  an  aggregation  :  it  is  one  or  the  other,  according  to  the  tenoiu'  of 
the  ideal  or  experimental  analysis  to  which  it  is  submitted. 

In  the  universe  nothing  is  isolated  ;  every  system  is  united  to  other  systems 
by  bonds  external  to  itself  ;  if  these  bonds  with  the  exterior  are  broken,  the 
system  appears  as  a  vmity  ;  if  again,  its  internal  ties  be  abolished,  it  is  resolved 
into  its  component  elements. 

All  the  developments  which  follow  each  other  in  the  nervous  system  show 
that  tlais  view  is  correct :  the  system  contains  bonds  of  union  by  wliich  it  is 
comiected  with  the  external  world  ;  on  the  other  hand,  its  constituent  parts  are 
united  together  in  such  a  way  as  to  form  a  unity  of  which  we  are  ourselves 
coruscious. 

The  conception  of  an  element. — Taken  in  an  absolute  sense,  the  word  element 
signifies  the  irreducible  limit  to  which  analysis  in  a  given  science  leads  vis.  Re- 
garded in  a  relative  sense,  it  signifies  some  component  part  which  analysis  has 
isolated  from  a  systematized  whole.  In  an  organized  whole,  such  as  the  living 
being,  the  component  parts  which  analysis  demonstrates  are  themselves  organ- 
ized wlioles,  are  systems  in  the  real  sense  of  the  word,  and  these  systems  may  be 


116  SYSTEMATIC  FUNCTIONS 

themselves  resolved  into  still  more  simple  systems.  Biologists  frequently 
describe  the  elements  as  the  component  cells  of  the  tissues.  In  spite  of  the 
fact  that  it  is  now  understood  that  the  cell  is  not  an  ultimate  element,  but  that 
it  is  itself  a  system  of  microscopic  dimensions,  this  term  will  be  employed,  because, 
in  biological  analysis,  the  cell  expresses  a  limit  far  better  characterized  than  any 
other  ;  this  is  dvxe  to  its  boundaries  being  well  defined  and  to  its  clearly  being  a 
\xnit. 

Thus  the  nervous  system  is  composed  of  partial  or  sub-systems,  m.ore  or  less 
resembling  it,  and  analysis  of  these  partial  systems  leads  us,  as  in  the  case  of  other 
apj^aratus,  to  cellular  elements.  These  elements  have  been  studied  in  the  first 
part  of  this  work  and  now,  being  better  known  as  regards  their  limits  and  consti- 
tution, are  described  as  neurons.  We  have  seen  that,  far  from  being  homogeneous 
and  incapable  of  subdivision,  they  present  an  internal  organization  and  differen- 
tiated functions. 

The  conception  of  function.  —  In  the  living  being  all  is  function,  because  in  it 
the  whole  tends  to  a  determinate  end.  The  idea  of  function  is  closely  connected 
with  and  is  superposed  to  that  of  system.  Function  represents  the  dynamic 
aspect  of  the  living  being,  whose  system  represents  the  static  aspect  ;  it  is 
nothing  else  than  the  bond  of  union  which  co-ordinates  the  several  portions 
of  a  system  and  confers  on  it  its  unity. 

Two  kinds  of  function.  —  The  study  of  the  organism,  that  of  its  nervous  system 
which  reproduces  its  chief  features,  that  of  the  partial  systems  into  which  it  can 
be  decomposed,  shows  that  there  are  in  it  two  kinds  of  bonds  of  union :  some 
entirely  internal,  unite  the  different  portions  of  the  system  so  that  its  unity 
results  ;  others,  external,  connect  it  with  still  larger  aggregations,  on  which  it 
depends  and  of  which  it  forms  part.  Thus,  from  the  very  nature  of  things,  there 
must  always  be  two  kinds  of  fvmctions  ;  the  first,  of  a  purely  internal  order,  are 
called  those  of  conservation,  which  in  living  beings  may  be  generally  described 
as  functions  of  nutrition  ;  the  second  are,  on  the  contrary,  functions  of  external 
relation,  or  of  relation  properly  so  called,  of  the  organism  or  of  the  system  under 
consideration  with  other  organs  and  other  systems  of  the  same  value. 

External  and  internal  relations. — It  is  perfectly  obvious  that  the  nervous 
system  possesses  these  two  orders  of  relationships  and  of  functions.  By  it  we 
are  brought  into  relationship  with  our  fellow-creatures,  and  it  connects  the  com- 
Ijonent  parts  of  our  being  by  its  internal  bonds  of  union.  But  in  proportion  as 
we  resolve  it,  by  experiment,  or  merely  by  thought,  into  its  component  sub- 
systems of  continually  decreasing  importance,  the  two  orders  of  function  become 
attributable  to  each  of  these  units  ;  each  of  these  has  its  functions  of  conserva- 
tion and  of  relation,  and  the  same  function  is  at  once  that  of  relation  and  that  of 
conservation,  according  as  to  whether  the  organs  which  it  tmites  are  regarded 
as  separate  systems  or  as  a  coherent  whole. 

Plasticity  of  the  nervous  system. — And,  as  a  matter  of  fact,  these  systems  are 
susceptible  of  isolation  and  of  fusion  ;  thanks  to  the  extreme  plasticity  of  the 
nervous  system,  they  approximate  or  separate  according  to  extremely  varied 
modes.  Without  absolutely  breaking,  the  bonds  of  union  relax  at  certain  places 
while  they  become  stronger  at  others.  On  account  of  this  mobility  and  this 
gradation,  the  study  of  the  fiinctions  of  the  systems  is  extremely  difficult,  but 
is  none  the  less  essential.  In  order  to  thoroughly  understand  it,  it  must  be  borne 
in  mind  that  the  phenomena  of  conscious  sensation  render  necessary  the  associa- 
tion of  a  large  number  of  co-ordinated  elements  ;  in  other  words,  they  are  only 
developed  in  systematized  assemblages  of  neurons.  If,  indeed,  movement  is 
everywhere  present  (whether  visible  or  invisible)  in  cellular  function,  it  is  not 
the  same  as  regards  consciousness  :  conscious  functicms  are  essentially  systematic 
functions. 


PRIMARY    DATA  117 

PRIMARY  DATA 

Relations  of  sensation  and  of  movement. — Whether  functions  express  external 
or  internal  relations  of  the  organism,  that  is  to  say,  external  or  internal  to  a 
definite  system,  they  are  all  based  on  fixed  relations  between  those  two  pheno- 
mena which  are  knowTi  as  movement  and  sensation.  On  the  more  or  less  com- 
plicated bond  of  union  which  exists  between  these  two  phenomena  depends  the 
importance  of  the  function,  and  that  of  the  system  which  brings  it  into  being. 
In  proportion  as  the  organization  becomes  more  complicated,  that  is  to  say, 
as  the  system  becomes  more  closely  united  and  superposed,  the  sensory  pheno- 
menon becomes  more  obvious  and,  in  its  turn,  presides  over  more  differentiated 
iind  more  varied  movements.  This  will  be  made  clearly  evident  by  analytical 
and  detailed  study  of  each  one  of  the  functions  of  the  system.  Only,  in  order 
to  make  this  study  more  intelligible  in  proportion  to  the  extent  to  which  it  is 
carried,  it  is  necessary  to  recall  some  definitions  and  to  clear  up  certain  pomts 
concerning  the  two  phenomena  which  are  essential  to  the  performance  of  every 
function  of  the  living  being. 

The  study  of  the  fxmction  of  innervation  brings  us  face  to  face  with  two  cate- 
gories of  facts  which  our  present  means  of  observation  and  of  analysis  are  unable 
to  further  resolve  :  these  are  on  the  one  hand  motion,  and  on  the  other  hand 
sensation.  Not  that  this  study  does  not  enable  us  to  recognize  at  every  moment 
theii-  relations  and  their  dependences  ;  but,  doubtless,  tlirough  the  imperfection 
of  the  information  which  it  supplies  concerning  both,  it  does  not  suffice  to  fill 
up  the  gap  which  separates  them  ;  hence  it  is  necessary  to  accept  the  phenomenal 
dviality  which  cUstinguishes  them. 

Origin  of  the  two  ideas. — The  idea  of  movement  comes  to  us  primarily  from 
the  exterior.  Our  o^^^l  special  movements  are  only  known  to  us  as  such  artifi- 
cially and  by  reasoning  (reciprocal  control  of  the  different  senses)  ;  as  regards 
the  inmost  movements  of  our  being,  we  can  and  shall  attain  a  knowledge  of 
them  only  by  employment  with  ever-increasing  assiduity  of  efforts  of  reasoning 
and  of  scientific  analysis. 

On  the  other  hand,  sensation  is  a  fact  internal  to  ourselves.  The  sensations 
of  others,  similar  to  those  which  we  j^erceive  in  om-selves,  are  only  kno-wTi  to  us 
artificially  and  by  reasoning  (by  comparison  of  the  motor  effects  of  these  sensa- 
tions in  ourselves  and  in  them)  ;  as  regards  the  most  elementary  sensations  of 
beings  other  than  ourselves,  they  are  and  will  be  known  to  us  only  by  continued 
efforts  of  reasoning  and  of  scientific  analysis  ;  the  method  of  study  of  the  two 
l^henomena,  however  contrary  these  phenomena  may  be,  cannot  differ  funda- 
mentally. 

In  short,  we  clearly  perceive  that  external  movement  is  continued  in  our- 
selves, and  that  sensation  exists  apart  from  ourselves  ;  but  we  do  not  succeed 
in  our  efforts  to  superpose  the  two  phenomena  (neither  in  nor  externally  to  our- 
selves) so  precisely  that  the  two  may  seem  to  us  as  being  merely  two  points  of 
view,  two  aspects,  two  varieties  of  one  and  the  same  thing,  instead  of  being  two 
distinct  categories  of  phenomena  incapable  of  resolution. 

Anatysis  of  the  two  phenomena. — In  the  present  state  of  our  knowledge,  the 
study  of  movement  is  infinitely  more  advanced  than  is  that  of  sensation.  Hence 
movement  serves  not  mereh^  as  a  control,  but  also  as  a  model  for  the  study  of 
sensation. 

We  know  that  complex  movements  are  capable  of  resolution  into  simpler  ones, 
and  that  this  decomposition  may  be  carried  to  a  greater  or  lesser  extent,  without 
om'  being  able  to  arrive  at,  in  an  absolutelj^  certain  manner,  the  first  elements  of 
movement.  It  is  the  same  as  regards  sensation  :  there  are  complex  sensations 
which  surround  elements  capable  of  isolation,  themselves  more  or  less  easily 
decomposable  into  still  simpler  elements.      It  is  obvious  at  the  first  glance  that 


118  SYSTEMATIC  FUNCTIONS 

analysis  may  be  carried  much  farther  in  the  case  of  movement  than  in  that  of 
sensation.  For  a  sensation  to  be  presented  to  ovir  consciousness,  it  is  necessarj^ 
that  it  arise  in  a  nervous  field  developed  in  a  very  complex  organization.  On 
the  contrary,  if  we  endeavour  to  study  synthetically  the  movements  which  corre- 
spond to  it,  especially  in  the  nervous  system,  we  shall  be  greatly  hindered  in  our 
efforts.!  Once  more,  the  two  orders  of  perception  approximate  one  another, 
but  the  boundaries  between  them  overlie  one  another,  but  are  not  sujjerposed. 

Process  of  association. — The  most  simple  sensation  of  which  we  are  conscious 
is  thus,  in  itself,  complex,  and  this  complexity  conceals  a  progressive  series  of 
_  ojDerations  in  some  degree  based  on  the  unity  of  the  result.  To  adopt  the  more 
concrete  language  of  anatomy,  sensation  is  not  a  cellular  phenomenon,  it  is  a  sys- 
tematic function. — If  sensation  is  real,  it  implies  the  association  of  elements  which 
proceed  from  one  of  our  senses  to  the  cerebral  cortex  ;  if  it  is  a  recalled  sensation, 
a  memory,  it  implies  the  co-operation  of  cerebral  elements  appertaining  at  least 
to  the  cortex,  and  perhaps  to  other  portions  of  the  brain,  for  in  this  case  the  limit 
is  not  easily  determined.  In  any  case  it  is  a  phenomenon  of  evolution,  which 
implies  a  process  of  association  as  regards  the  cellular  elements  of  the  nervous 
system,  or,  more  exactly,  of  the  dynamic  unities  corresponding  to  their  cellular 
unities. 

Threshold  of  consciousness. — Consciousness  has  its  degrees  just  as  its  field 
has  also  its  variable  limits.  Every  act  which  takes  place  in  ourselves  and  of 
which  we  are  not  conscious  may  become  conscious  by  the  mechanism  of  the 
internal  phenomenon  which  is  known  as  attention.  A  moment  ago,  this  act  was 
below  the  threshold  of  consciousness  ;  then  it  has  attained  the  level  in  which 
it  becomes  clearly  conscious.  This  threshold  corresponds  therefore  to  a 
degree  of  consciousness  somewhat  arbitrarily  fixed,  in  order  to  eliminate  from 
the  consciousness  everything  which  has  only  a  doubtful  value  or  is  perceptible  with 
difficulty.  Practically,  w^e  relegate  to  the  unconscious  all  bare  consciousness  of 
the  being,  and  we  retain  the  name  conscious  for  the  recognition,  more  or  less 
analytical  and  detailed,  of  the  being. 

Simple  sensation. — If  sensation  presents  degrees  and  shades  in  its  intensity,  it 
presents  yet  more  of  these  in  its  complexity.  We  accept,  as  we  have  said,  as 
elementary  a  fact  which  we  know  is  fundamentally  complex,  but  which  resists 
that  internal  analysis  to  which  we  endeavour  to  subject  it  in  ourselves.  This 
fact  is  what  is  known  as  simple  sensation.  The  prick  of  a  needle,  the  sight  of  a 
luminous  point,  the  hearing  of  a  short  sound,  supply  us  with  ordinary  examples 
of  it.  Simple  sensation  is  yet  accompanied  with  perception  ;  the  object  is  per- 
ceived as  being  such  in  its  owti  character  ;  that  is  to  say,  it  is  recognized.  If 
perception  is  wanting,  there  is  merely  crude  sensation. 

Specific  modalities. — These  different  examples  of  sensation,  touch,  light,  sound, 
etc.,  represent  what  is  known  as  specific  varieties  (incapable  of  reduction  the 
one  into  the  other)  of  sensation  ;  further,  each  one  of  thein  may  include  various 
gradations  (colour,  tonality,  etc.). 

Complex  sensations.- — Simple  sensations  of  varying  gradations  combine  among 
themselves  to  form  complex  sensations,  in  which  the  component  elements  are 
so  fvised  together  as  no  longer  to  apjDear  distinct  from  one  another  ;  every  sense 
furnishes  examples  of  this  nature.  The  sjiecific  sensations  of  the  different  senses 
are  combined,  in  their  turn,  to  form  a  jDhenomenon  which  no  longer  bears  the 

1  If  this  should  cause  surprise,  it  must  be  remembered  that  our  organism  is  constructed 
for  a  practical  and  not  for  a  speciilative  end.  Sensations  which  should  be  localized  in 
areas  which  sliould  correspond  to  our  component  cells  would  be,  by  their  excessive  accuracy 
of  localization,  useless  to  us  ;  just  as  direct  syntlietic  vision  of  movements  which  corre- 
spond to  an  ordinary  sensation  would  distract  us  from  the  consideration  of  much  more 
simple  external  movements,  which  it  is  important  for  us,  on  the  contrary,  to  be  acquainted 
with. 


PRIMARY    DATA  119 

name  of  sensation  and  wliich  marks  definite  progress  in  the  evolution  of  this 
series  of  internal  j^henomena. 

Idea. — By  their  association,  these  sensations,  whose  form,  source  and  com- 
plexity are  so  different,  give  origin  in  their  turn  to  a  new  psychical  process  still 
more  complex  than  themselves  ;  this  is  ideation.  The  origin  of  sensation,  start- 
ing from  these  elements,  is  unkno-mi  to  us  as  regards  its  mechanism,  because 
they  themselves  are  not  accessible  to  consciousness  :  in  other  words,  conscious- 
ness onh^  becomes  clear  in  proportion  as  these  elements  are  associated  in  a  sensa- 
tion :  when  isolated,  they  elude  it.  The  genesis  of  ideation,  by  the  association 
of  sensations,  becomes  on  the  other  hand  accessible  to  internal  observation. 
Psychology  has  always  extensively  employed  this  method,  in  order  to  study  the 
formation  of  ideas.  At  the  present  time  progress  in  this  direction  has  been 
made  by  causing  external  observation  and  experiment  to  be  made  use  of  in  this 
study.  In  man  and  animals  lesions  of  the  nervous  system  either  exist  or  are 
induced  experimentally,  by  which  these  complex  manifestations  of  consciousness 
are  disconnected,  the  one  being  suppressed,  the  others  being  allowed  to  continue  ; 
and  thus  we  gain  an  insight,  although  a  feeble,  and  too  often  uncertain  one, 
concerning  the  conditions  of  their  existence. 

Cognition  ;  Recognition. — The  psychical  elements  which  form  sensations  and 
ideas  are  not  merely  associated  in  an  actual  and  contemporaneous  fashion,  but 
also  tlie  regular  functional  activity  of  the  nervous  system  further  provides  them 
with  a  bond,  an  association,  originating  therefore  a  continuity  in  time.  New 
ideas  and  sensations  which  arise  in  us  recall  the  existence  of  sensations  and  of 
anterior  ideas  of  the  same  order  ;  we  recognize  the  objects,  movements,  pheno- 
mena, symbols  which  have  already  made  an  impression  upon  us,  when  this 
imjDression  is  renewed.  This  recall  of  sensations  and  of  previous  ideas,  which 
seemed  to  be  effaced,  implies  that  they  were  in  reality  preserved  in  a  latent  dis- 
sinuilated  condition,  which  is  called,  specifically,  the  unconsciotts  state.  New 
impressions  bring  them  back  to  the  tlu-eshold  of  consciousness.  This  is  the 
rememljrance  or  recognition  of  phenomena  with  which  we  have  already  been 
in  touch. 

Residue. — In  other  words,  every  impression,  every  sensation  leaves  a  residue 
in  VIS.  New  sensations  of  the  same  order  are  added  to  it,  conseqviently  are  asso- 
ciated in  it,  by  recalling  it  to  actuality.  This  identification  of  the  new  pheno- 
menon with  the  old  through  time  permits  us  to  recognize  it ;  were  tliis  identifica- 
tion wanting,  there  would  be  for  us  no  experience  of  the  past,  the  action  of  the 
external  world  on  our  senses  would  be  continually  a  new  one,  that  is  to  say,  one 
perpetually  unknown. 

Remark. — It  may  seem  that  these  data  on  psychical  processes  would  be  more 
appropriately  placed  at  the  end  of  the  study  of  the  nervous  functions,  as  being 
its  finishing  point,  and  not  at  its  commencement.  We  shall  meet  with  them 
again  in  the  analysis  of  a  certain  number  of  special  cases,  particularly  the  func- 
tion of  language  ;  but  from  the  very  first  steps  wliich  we  shall  take  in  this  study, 
it  is  precisely  these  phenomena  of  sensation  that  we  meet  with,  occurring  as  they 
do  as  the  inevitable  consequence  of  every  investigation,  of  every  analysis  of  the 
nervous  system.  In  the  study  of  moveinent  we  may,  if  we  wish,  proceed  from 
the  simple  to  the  compound  ;  in  the  order  of  sensation,  an  already  synthetized 
phenomenon  is  offered  us,  as  the  first  discernible  dattun.  Hence  we  are  com- 
pelled to  describe  it  smmnarily  at  first,  at  the  risk  of  being  forced  to  justify  ovir 
affirmations,  in  proportion  as  the  facts  resulting  from  observation  and  experi- 
ment shall  be  displayed  before  us.  Less  than  any  other  science  can  psychology 
proceed  by  deduction  ;  in  the  living  being  everything  is  allied,  everything  is 
closely  connected  ;  hence  it  results  that,  in  the  study  of  its  fiinctions,  we  must 
joroceed  from  the  comjDlex  to  the  simple  in  many  cases. 


FIRST  SECTION 
NERVOUS    ORGANIZATION 

At  the  foundation  of  nervous  organization  lies  a  bond  of  union,  a 
reciprocal  dependence  between  sensation  and  motion.  Its  perfection 
is  obtained  through  multiple  and  graduated  forms  which  affect  both 
phenomena,  as  also  from  the  numberless  associations  wliich  they  are 
capable  of  effecting.  The  centripetal  paths  convey  impulses  which 
are  from  their  origin  both  multiple  and  diverse  (sense  organs)  ;  the 
centrifugal  routes  terminate  in  muscles  (or  equivalent  organs),  them- 
selves both  numerous  and  diverse,  for  the  performance  of  visible  or 
concealed  acts,  which  indicate  the  end  of  the  evolution  of  the  nervous 
process.  From  the  commencement  to  the  end  of  the  latter  sensory 
phenomena  are  interpolated  ;  its  value  increases  with  the  complica- 
tion of  the  nervous  paths,  followed  by  the  impulse,  and  also  by  the 
length  of  time  which  it  occupies  in  these  paths. 

This  complication  is  based  on  a  regular  system  ;  it  proceeds  on 
simple  lines  and  on  a  plan,  the  object  of  which  can  be  recognized.  First 
of  aU  it  is  necessary  to  describe  this  general  plan,  by  which  the  organiza- 
tion of  impulses  is  rendered  intelligible.  By  adding  to  it  the  data 
furnished  by  experiment,  we  shall  be  able  to  observe  the  progress  of 
these  latter,  their  results  now  divergent,  now  parallel,  and  again  diver- 
gent ;  their  numerous  conflicts  ;  their  reinforcements  ;  their  divisions 
and  their  postponements  :  all  the  circumstances  which  do  not  explain 
to  us  these  results  of  internal  observation  which  we  describe  as 
sensation  and  ideation,  yet  which  manifestly  give  rise  to  them  and  give 
us  command  of  them  in  experimental  practice,  and,  nowadays,  in 
the  treatment  of  nervous  diseases. 

Its  scheme. — Anatomically  a  distinction  is  made  between  a  peri- 
pheral nervous  system  and  a  deep  nervous  system  (the  latter  being 
generally  known  as  central). 

(a)  Inferior  system. — This  distinction  is  justified  physiologically  on  the  condi- 
tion of  a  division  being  made,  not  at  the  termination  and  at  the  apparent  origin 
of  the  sensory  and  motor  roots,  but  at  their  real  termination  and  origin  in  the 
grey  substance  of  the  medulla  oblongata  and  spinal  cord.  The  conventional 
limit  of  the  two  systems  is  defined  in  this  grey  matter. 

The  long  cylinder  which  the  latter  forms  is  the  direct  rendezvous  of  periplieral 

120 


NERVOUS    ORGANIZATION  121 

impressions,  and  is  at  the  same  time  tlie  point  of  immediate  departure  of  the 
motor  reactions  ;  it  is  a  spot  in  whicli  the  imjaulses  are  systematized  and  organ- 
ized ;    it  is  the  keystone  of  the  peripheral  or  inferior  system. 

(b)  Superior  system. — Another  locality,  in  which  grey  matter,  assuming  the 
form  of  a  folded  sphere,  is  found,  is  the  surface  of  the  brain,  and  is  united  to  the 
preceding  by  connexions  in  which  the  conduction  is,  on  the  one  hand,  ascending 
and  on  the  other  descending,  by  which  impulses  are  conveyed  to  it  and  by  which 
they  are  carried  from  it.  It  has  no  communication  with  the  exterior  except  in 
an  indirect  and  mediate  manner  ;  it  works  on  the  niaterials  prepared  by  the  grey 
axis,  to  which  it  gives  a  new  organization,  and  it  reacts  on  the  exterior  by  the 
intermediation  of  this  same  grey  axis,  whose  motor  associations,  also  ready 
prepared,  it  makes  use  of :  it  is  the  keystone  of  the  deep  or  superior  system. 

T)ie  conductors  which  carry  the  impulse  (in  two  different  directions)  between 
the  periphery  and  the  grey  axis  are  the  so-called  fibres  of  projection  of  the  first 
order.  Those  which  convey  it  between  the  two  areas,  previously  pointed  out, 
of  the  grey  matter  are  fibres  of  projection  of  the  second  order. 

Extension  of  the  grey  axis  beyond  the  spinal  column. — Ganglia  of  the  great 
sympathetic. — This  very  simple  scheme  requires  some  corrections  and  additions 
in  order  to  accT.U'ately  represent  the  real  condition.  Externally  to  the  spinal 
canal,  the  gi'ey  axis  is  prolonged  in  the  form  of  small  gi'ey  disseminated  masses, 
the  ganglia  of  the  great  sympathetic,  which  jaossess  the  sensori-motor  functions 
of  the  spinal  cord. 

Superior  prolongations  of  the  grey  axis. — High  up,  above  the  medvilla  oblon- 
gata, the  grey  axis,  after  it  has  gathered  together  all  the  conductors  of  general 
sensation,  is  surmounted  by  discontinuous  masses  (the  internal  and  external 
geniculate  bodies,  the  corpora  qv/xdrigemina,  anterior  and  posterior,  the  mam- 
millary  bodies),  which  appertain  to  the  special  senses  (hearing,  vision,  smell) 
and  form,  from  a  fmictional  point  of  view,  differentiated  prolongations  of  this 
same  axis.  Still  higher  occm"s  an  important  grey  mass,  the  optic  thalamus,  which 
introduces  a  new  complication  into  this  edifice,  hitherto  apparently  so  simple. 
This  mass,  composed  of  distinct  areas,  of  which  each  belongs  to  one  of  the  modes 
of  sensation  which  are  diffused  through  the  nervous  system,  is  no  longer  placed 
at  the  union  of  the  fibres  of  projection  of  the  first  and  second  order,  but  in  the 
very  coui-se  of  these  latter.  To  express  the  matter  more  clearly,  the  ascending 
or  sensory  fibres,  which  proceed  from  the  grey  axis  to  the  cerebral  cortex,  are 
inteiTupted  in  the  optic  thalamus,  the  larger  proportion  of  them  as  regards  the 
majority  of  observers,  entirely  for  others.  This  very  obvious  interruption  is 
not  the  only  one  which  the  paths  of  ascending  imjaulses  undergo  ;  similar  inter- 
i-uptions  are  found  from  the  spinal  cord,  so  that  these  paths  are  divided  into  two 
species  :  the  one  long,  proceeding  from  the  grey  axis  to  the  cortex,  the  other 
short,  whose  length  varies  according  to  circumstances. 

Another  organ,  which  must  also  be  regarded  as  possessing  the  importance  of  a 
system,  is  the  cerebellum,  which,  through  the  connexions  uniting  it  to  the  grey 
axis  and  to  the  cortex,  comi^licates  yet  more  this  assemblage,  which  is  known, 
in  its  totality,  as  the  superior  or  dee}?  system.  In  every  case,  the  covu-se  of  the 
impulses  which  traverse  this  suj^erior  system  is  extremely  varied  and,  from  this 
point  of  view,  contrasts  with  the  relative  simplicity  of  their  progress  in  the 
inferior  systein. 

Equivalent  juxtaposed  systems. — In  addition  to  the  divsions  which  have  just 
been  pointed  out,  the  nervous  systeni  possesses  yet  others  in  a  quite  different 
direction.  In  addition  to  the  transverse  incisions  marking  its  stages,  it  displays 
fissm-es  on  its  length  which  also  have  the  value  of  differentiated  systems.  At  its 
origin  in  the  organs  of  sense,  the  nervous  system  affects  territories  as  well  as  func- 
tions which  are  distinctly  separated  ;    at  the  surface  of  the  brain,  the  cortex  (a 


122  SYSTEMATIC    FUNCTIONS 

remarkable  fact)  reproduces  these  divisions.  It  reproduces  them  by  repeating, 
not  merely  the  areas  devoted  to  each  sense,  but  certain  topographical  divisions 
and  subdivisions  of  these  territories  themselves.  The  brain  is  metamerised  like 
the  spinal  cord,  the  word  metamerised  being  used,  it  is  true,  in  its  most  general 
and  not  in  its  strictly  embryological  meaning.  The  optic  thalamus  offers  a 
similar  metamerisation,  repeating  that  of  the  sensory,  peripheral,  medullary  and, 
lastly,  cortical  sensory  territories.  The  cerebellum,  the  least  metamerised  of 
these  grey  masses,  has  more  special  connexions  with  some  senses  than  with 
others  (equilibrium,  sight,  touch). 

Association  of  the  systems. — Such  is  the  plan,  once  again  very  simple,  which 
divides  the  nervovis  system  into  systems,  no  longer  superposed,  but  juxtaposed, 
which  I'eceive  from  the  preceding  ones  their  constituent  elements.  But  once 
again,  also,  it  must  be  repeated  that  these  are  merely  the  chief  constructive 
outlines.  They  supjDort  others,  which  ensure  the  multiple  connexions  between 
these  equivalent  bvit  specifically  differentiated  systems,  \vhich  they  render  more 
obvious  to  us.  From  the  spinal  cord,  the  impulses  coming  from  the  periphery 
are  co-ordinated  by  associations  effected  in  the  grey  matter  of  the  cord,  and 
the  impulses  which,  from  the  spinal  cord  are  forwarded  to  the  muscles,  are  in  the 
same  way  organized  by  it.  Of  the  original  metamerisation  of  the  sj^inal  cord, 
but  little  remains  in  the  case  of  the  superior  mammals,  and  above  all  in  man,  at 
the  period  of  their  complete  development.  The  segments  of  the  grey  axis  are 
fused  into  more  and  more  niunerous  functional  associations,  and  special  condi- 
tions must  be  present  in  order  that  the  isolated  function  of  these  segments  may 
be  recognized.  The  optic  thalamus  presents  connexions  of  the  same  kind,  but 
still  more  marked.  This  mass  of  grey  substance  no  longer  collects  merely  the 
impressions  arising  from  a  single  sovu-ce,  like  the  spinal  cord,  the  geniculate  bodies 
and  the  corpora  quadrigemina,  but  all  those  proceeding  from  all  the  senses  which 
are  rej^resented  in  it  and  which  are  in  a  certain  measure  organized  therein.  This 
great  ganglion  is  qualified  for  the  reflection  of  these  impressions,  when  trans- 
formed, upon  the  organs  of  motion  ;  an  essential  role  is  attributed  to  it  as  regards- 
instinctive  and  emotional  manifestations. 

In  man  the  most  i:)owerful  organ  of  association  is  the  brain.  The  sensorial 
systems,  which  terminate  in  its  cortex,  find  in  it  and  in  the  tangential  fibres 
immediately  subjacent  to  it  those  internal  connexions  which  organize  them. 
These  same  systems  find  in  the  commissures  of  varying  lengths  and  direction 
which  fiU"row  the  cerebral  mass,  the  links  which,  in  their  turn,  fuse  them  into  a 
common  functional  activity. 

Functional  localizations.  —  The  nervous  system  is  composed  of  unities,  of 
elements,  which,  from  the  first  to  the  last,  have  a  differentiated  function  and  one 
in  a  certain  sense  specific.  But  this  differentiation  is  generally  progressive  and 
graduated,  and  resides  principally  in  the  connexion  of  these  elements  amongst 
themselves.  For  convenience  of  study,  we  sometimes  voluntarily  neglect  these 
graduations,  in  order  to  collect  together  the  objects  and  the  phenomena  imder 
a  common  type  ;  again,  on  the  contrary,  we  give  them  undue  imjDortance  in 
order  to  mark,  in  the  two  cases,  that  distinction  which  is  api^roj^riate  between 
them  ;  for,  otherwise,  the  infinite  detail  would  lead  to  confusion.  Hence  have 
arisen  the  discussions  between  those  who  would  localize  and  those  who  would 
not  localize  nervous  functions,  discussions  arising  miich  more  from  the  exaggera- 
tion of  the  individual  point  of  view  than  from  absolute  error. 

Three  points  of  view. — In  order  to  render  these  discussions  intelligible,  it  is 
necessary  to  clearly  understand  the  natm-e  of  system  and  of  function,  such  as- 
has  been  pointed  out  above.  As  regards  the  nervous  system,  three  points  of 
view  which  should  be  separated  have  often  been  confounded.     These  three  points- 


NERVOUS   ORGANIZATION  123 

of  view  regard,  tlie  first  the  succession  of  phenomena,  the  second  their  equivaleyice, 
the  third  their  gradation  ;  hence  arise  tliree  orders  of  locahzation  which  have 
not  ahvays  been  properly  distinguished. 

(a)  The  several  jaortions  of  the  nervous  system  transmit  acti\itj'  in  a  definite 
direction.  In  this  evolution  sensation  first  appears,  then  the  apparent  move- 
ment by  which  functions  are  exercised  ;  hence  we  recognize  in  the  nervous  system 
a  sensory  portion  and  a  motor  portion  successively  arranged. 

(6)  In  the  nervous  system  sensation  and  motion  manifest  different  modalities 
which  are  developed  in  parallel  and  equivalent  systems.  The  idea  of  localization 
corresponds  above  all  to  the  distinction  of  these  systems  as  ordinarily  under- 
stood, that  is  to  say,  in  so  far  as  these  systems  become  flush  with  the  cerebral 
cortex  at  their  superior  terminations. 

(c)  Lastly,  whatever  may  be  the  order  of  sensation  wliich  governs  the  motor 
act  (whatever  may  be  the  sensorial  organ  which  furnishes  the  impressions)  this 
sensation  manifests  degrees  according  to  the  more  or  less  deep  routes  in  which 
the  impulses  received  in  the  organs  of  sense  travel  ;  in  other  words,  according 
to  the  height  at  which  the  impulses  are  reflected  ;  whence  the  division  of  acts 
into  new  categories  of  unequal  value,  of  which  the  three  principal  are,  from  this 
jDoint  of  view,  called  automatic  (reflection  in  the  spinal  cord),  instinctive  (reflec- 
tion in  the  oj^tic  thalamus),  vohmtary  (reflection  in  the  cerebral  cortex).  Con- 
sciousness has  its  degrees,  which  are  determined  by  the  more  or  less  complex 
organization  of  impulses. 

Restriction. — None  of  these  indications  must  be  taken  in  an  absolute  sense  ; 
not  one  of  the  phenomena  to  which  they  relate  is  an  isolated  one  ;  none  of  the 
sj^stems  which  support  them  is  absolutely  inde]iendent  ;  all  mutually  influence 
each  other. 

Every  time  that  some  part  of  the  nervous  system  is  stimulated  or  suppressed 
there  is  at  all  events  a  temjiorary  reaction  of  this  modification  on  the  whole 
system.  This  reaction  is  immediate  or  remote,  and,  in  the  latter  case,  is  often 
so  weak  as  to  be  inajDpreciable.  The  pertvu'bation  thus  induced  varies  according 
to  the  jDart  of  the  nervous  system  which  has  been  modified.  Hence  the  inference 
may  reasonably  be  drawn  that  the  portions  experimented  upon  possess  different 
functions.  But  the  argument  is  often  carried  still  farther,  the  function  being 
localized  in  the  region  experimentally  modified,  which  has  been  the  point  of  depar- 
ture of  the  observed  disorder,  and  in  doing  this  it  is  clear  that  the  teachings  of 
experiment  are  overstepped.  The  ner\-ous  system  is  composed  of  parts  which 
are  at  the  same  tune  botli  conjoint  and  functionally  differentiated. 


CHAPTER  I 

SENSATION   AND   MOTION— THEIR   RELATIONSHIPS 

The  ego  in  itself  only  perceives  sensations,  outside  itself  it  only  perceives 
movements.  The  movements  of  our  own  limbs  would  be  for  it  merely 
those  of  foreign  bodies  were  it  not  for  the  sensations  which  attach  them 
to  it  and,  indeed,  they  become  such  with  regard  to  the  ego  when  they 
are  no  longer  sensitive.  How  does  our  ego  recognize  the  existence  of 
sensation  in  the  case  of  beings  other  than  ourselves  ?  By  a  process 
of  reasoning  founded  on  analogy,  and  not  otherwise. 

Analogical  proof. — If  I  wound  an  animal  and  it  begins  to  struggle  and  cry, 
I  say,  without  any  doubt,  that  it  feels  ;  seeing  that  it  manifests  the  same  reac- 
tions as  those  by  wliich  I  express  my  own  sensibility,  I  affirm  that  it  also  possesses 
the  same,  and  I  am  able  to  estimate  the  quality  and  the  amount  of  the  sensation. 
Between  it  and  inyself,  as  between  myself  and  it,  there  is  merely  movement  ; 
but  in  myself  there  is  a  definite  link  between  sensation  and  movement,  and  this 
enables  me  to  recognize  sensation  by  means  of  movement,  and  by  this  indirect 
means  to  estimate  it  as  a  fact  accessible  both  to  observation  and  experiment. 

Law  of  continuity. — The  more  closely  the  motor  reactions  of  the  being  are 
assimilated  to  mine,  the  greater  I  presume  to  be  the  resemblance  of  its  power 
of  sensation  with  my  own.  In  projDortion  as  this  resemblance  givfes  place  to  a 
more  remote  analogy,  so  does  the  an^iount  of  sensation  which  it  represents  become 
less  and  farther  removed  from  that  which  is  personal  to  myself.  If,  however, 
this  degradation  follows  a  regular  progression,  I  shall  then  be  in  a  position  to 
connect  the  fact  of  this  transformation  and  diminution  with  my  power  of  sensa- 
tion, which  is  the  only  criterion  available  to  me  for  estimating  facts  of  this  nature. 
It  is  the  same  with  sensation  as  with  life,  wliich  it  characterizes  :  we  see  its  field 
continually  increasing,  without  oiu*  being  able  to  precisely  define  its  limits  ;  and 
this  increase  is  effected,  at  each  new  stage,  by  the  adjunction  of  beings  of  a  nature 
at  the  same  time  inferior  and  analogous  to  that  of  beings  previously  considered 
as  being  of  the  most  elementary  structm-e. 

Anthropomorphic  reasoning. — Excej^t  for  the  infinitesimal  part  which  each 
one  of  us  plays  therein,  a  knowledge  of  the  living  world  is  based  on  antliropo- 
morphic  reasoning,  and  it  is  impossible  to  base  it  on  any  other  reasoning. 

Hence  it  is  necessary  to  exert  great  prudence  in  employing  it. 

A.     THE  ROOTS  OF    THE    NERVOUS    SYSTEM— THEIR    FUNCTIONS 

The  bond  of  union  between  sensation  and  motion  is,  in  a  living  being, 
an  obvious  fact. 

We  can  destroy  this  bond  ;    we  can  cause  movement  and  sensation 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    125 

to  reappear,  isolated  one  from  the  other,  bj^  making  use  of  different 
portions  of  the  nervous  system. 

I.     The  Simple  Facts  ;  General  Laws 

1.  Nerve  pairs. — The  nervous  system  with  its  superior  termination, 
the  brain  ;  its  fundamental  portion,  the  spinal  cord  ;  and  its  peripheral 
distribution,  the  nerves,  being  regarded  as  a  whole,  it  will  be  noticed 
that  these  last  are  inserted  along  the  whole  length  of  the  cord  on  each 
side  by  two  roots,  one  dorsal  (posterior  in  man,  superior  in  animals), 
the  other  ventral  (anterior  in  man,  inferior  in  animals).  These  are 
indeed  the  roots  of  the  nervous  system,  that  is  to  say,  the  paths  by 
which  the  relations  of  this  system  between  it  and  the  external  world 
and  with  the  exterior  are  established,  and  this  in  a  double  direction, 
and  conversely.  Thus  symmetrically  arranged,  they  form  nerve  pairs, 
one  on  each  side,  corresponding  to  each  of  the  metameric  divisions  of 
the  spinal  cord. 


/  P  ost.  root 


Fig.   49. — Two  nerve  pairss  at  their  origin  in  the  spinal  cord. 

roots. 


Anterior  and  posterior 


As  regards  the  upper  pair,  the  figure  shows  the  relations  of  the  roots  with  the  gvey  axis  and 
the  fluted  shape  of  the  latter.  In  the  lower  pair  is  seen  the  emergence  of  the  anterior  roots^'at 
the  surface  of  the  spinal  cord,  and  in  the  anterior  collateral  furrows. 

Distinct  functions. — For  a  very  long  time  it  was  supposed  that  these 
roots  had  different  functions,  and  h\^otheses  were  elaborated  with 
the  object  of  pointing  out  the  nature  of  these  functions. 

To  Ch.  Bell  (1811)  belongs  the  merit  of  invoking  the  aid  of  experiment 
in  order  to  solve  this  problem  ;   but,  operating  on  animals  at  the  very 


126  SYSTEMATIC  FUNCTIONS 

moment  in  which  they  were  killed  (rabbits  killed  by  distension  of  the 
medulla  oblongata),  he  was  not  able  to  determine  the  function  of  the 
posterior  roots,  which  he  considered  to  be  devoid  of  sensation,  and  he 
merely  detected  the  motor  excitability  of  the  anterior  roots,  which  he 
considered,  further,  to  be  sensitive. 

In  ordei'  to  understand  tlie  experiment  of  Ch.  Bell  and  the  signification  which 
he  attached  to  it,  it  is  necessary  to  be  cognisant  of  his  point  of  view.  Imbued 
witli  the  then  current  ideas  of  Willis  concerning  the  nervous  system,  he  endeav- 
oured to  verify  the  latter.  Willis  regarded  the  brain  as  the  centre  of  sensation 
and  of  movement,  while  the  cerebellum  presided  over  vital  actions  (circulation), 
nutrition,  secretion,  etc.).  Guided  by  anatomical  results,  Charles  Bell  described 
the  anterior  roots  as  being  conducting  paths  in  direct  continuation  with  -the 
brain  through  the  intermediation  of  the  crura  cerebri,  and  the  posterior  roots 
as  tracts  directly  connected  with  the  cerebrum  by  the  intermediation  of  the 
restiform  bodies  (it  is  now  known  that  in  reality  the  connexion  is  far  less  simple). 
The  anterior  roots  would  thus  represent  the  functions  of  the  brain  (sensation 
and  movement)  ;  the  jDosterior  roots  those  of  the  cerebellum  (phenomena  of 
nutrition). 

Experiment,  as  performed  by  Charles  Bell,  does  not  verify  all  these  assump- 
tions :  it  only  confirms  one  of  them,  the  motor  function  of  the  anterior  roots, 
but  remains  mute  as  regards  all  the  others.  On  this  account,  indeed,  it  did  not 
appear  to  liim  contrary  to  the  hypothesis  which  served  as  his  point  of  dejoarture  ; 
in  any  case,  it  seemed  to  liim  sufficient  to  support  the  doctrine  of  Willis,  which 
it  was  his  object  to  verify.  Ajiart  from  any  hypothesis,  however,  the  experiment 
of  Charles  Bell  established  a  fact  new  for  his  epoch,  namely,  that  the  anterior 
root  manifests  functions  which  are  not  displayed  by  the  posterior  root  ;  in  other 
words,  that  there  is  a  functional  difference  between  the  one  and  the  other  root. 
As  to  the  natvire  of  this  difference,  it  wholly  escaped  him.  It  did  not  become 
clearly  comprehensible  (for  him,  as  for  every  one  else)  until  some  years  later,  after 
the  researches  of  Magendie  on  this  subject. 

Nature  of  these  functions. — To  A.  Magendie  incontestably  belongs 
the  merit  of  having  ascertained  the  truth  on  this  point  through  his 
decisive  experiments  (1821).  ^ 

Exjjeriment. — The  experiment  is  easily  made  on  the  dog,  and  prefer- 
ably on  a  young  animal  (softness  of  the  bones,  length  of  the  roots  and 
the  special  arrangement  of  the  dura  mater,  which  directly  invests  the 
spinal  cord).  The  animal  is  anaesthetized  and  is  kept  insensible  during 
all  the  preliminary  operations. 

It  is  only  permitted  to  recover  consciousness  at  the  time  when  the 

1  In  France,  as  also  abroad,  the  discovery  of  the  separate  functions  of  the  nerve  roots 
is  generally  attributed  to  Charles  Bell.  As  a  matter  of  fact,  he  misconstrued  them,  and 
they  were  exactly  formulated  for  the  first  time  by  Magendie,  by  means  of  the  very  apt 
experiments  which  he  employed  to  demonstrate  them.  Tliis  has  been  recognized  and 
maintained  by  all  the  authors  wlio  have  studied  this  question  of  priority.  (Consult 
CI.  Bernard,  De  la  physiologie  generale,  pp.  15  and  216. — Vulpian,  Le(^ons  sur  la  physiologic 
ginerale  du  systeme  nerveux,  p.  109  et  suiw — Chauveau,  Journal  de  Vanatomie  et  de  la 
physiologie. — A.  Waller,  Elements  de  jjhysiologie  humaine,  p.  596.) 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    12: 


Co 


:^ 


roots  are  acted  upon.     A  limited  region  being  taken  for  investigation, 

as  that  of  the  posterior  hmbs,  the  ^ 

roots  of  the  nerves  which  correspond 

to  them  in  the  lumbo-sacral  region  of 

the  spinal  cord  are  laid  bare.     For 

example,  all  the   so-called   posterior 

roots    (superior   in   the   animal)    are 

cut  on  the  right,  and  on  the  left  all 

the  so-called  anterior  roots  (inferior 

in  the  animal). 

(a)  Effects  of  the  section  of  the 
roots. — x\s  a  result  of  these  sections, 
the  limb  on  the  right  side  continues 
to  move,  but  ceases  to  be  sensitive  ; 
it  may  be  pricked,  pressed  or  burnt 
without  provoking  reactions  on  the 
part  of  the  animal.  The  limb  on  the 
left  side  continues  to  be  sensitive, 
hut  ceases  to  move  ;  the  animal  is 
incapable  of  using  it  for  walking  or 
for  any  other  purpose. 

Hence  it  follows  that  the  posterior 
root  is  seyisory,  that  is  to  say  is 
connected  with  the  exercise  of-  sensa- 
tion ;  the  anterior  root  is  motor,  that 
is  to  say,  connected  with  the  per- 
formance of  movement. 

(b)  Effects  of  stimulation.  —  By 
cutting  the  posterior  and  anterior 
roots  we  have  not  destroyed  or  sup- 
pressed the  organs  of  sensation  and 
of  movement,  but  we  have  inter- 
rupted the  paths  by  which  the 
impulse  which  arouses  the  first  or 
excites  the  second  is  conveyed.  In- 
deed, if  the  central  end  of  a  posterior 
root  is  irritated,  the  animal  reacts, 
that  is  to  say,  feels  ;  if  the  peripheral 
end  of  an  anterior  root  is  irritated, 
the  corresponding  limb  is  moved. 

If,  conversely,  the  peripheral  end  of  a  posterior  root  is  irritated,  or 
the  central  end  of  an  anterior  root,  no  reaction  of  such  a  nature  as 


Fig.   50. — Medullary  roots  of  the  lum- 
bar and  sacral  regions  in  the  dog. 

The  diagram  shows  the  point  of  emerg- 
ence of  each  of  the  roots  from  the  spinal 
cord  in  relation  to  its  exit  from  the  inter- 
vertebral foramen.  Obliquity  and  relative 
length  of  the  sixth  and  seventh  lumbars 
and  the  first  sacral. 

Co,  last  rib.  1  to  7,  transverse  apophy- 
ses of  the  lumbar  vertebrae,  of  wliich  the 
posterior  arch  is  removed.     Is,  illiac  bone. 


128  SYSTEMATIC  FUNCTIONS 

those  which  have  just  been  referred  to,  either  sensory  or  motor,  results. 
By  this  second  test  a  new  conception,  and  a  very  important  one,  is 
added  to  that  of  separation  or  distinction  between  sensation  and  move- 
ment ;  that,  namely,  of  direction,  of  orientation,  or  of  polarization,  as 
it  is  generally  termed. 

Laws  of  Magendie.— 1.  The  posterior  or  dorsal  root  conducts  impulses 
from  the  periphery  to  the  central  portions  of  the  nervous  system,  to  the 
special  organs  of  sensation  ;   it  is  sensory. 

2.  The  anterior  or  ventral  root  conducts  impulses  from  the  central  portions 
to  the  periphery,  to  the  special  organs  of  movement ;  it  is  motor. 

Dynamic  polarity. — The  dynamic  polarity  of  the  neurons  has  no  other  experi- 
mental foundation  than  this.  We  now  say  of  the  neurons  that  which  it  has  been 
customary,  since  the  time  of  Magendie,  to  say  of  sensory  and  motor  fibres, 
nainely,  that  some  conduct  in  one  direction  and  others  in  the  other,  which 
presujjposes  two  poles  for  each.  It  is  true  that  anatomy  has  enabled  us  to 
observe  the  exact  situation  of  those  of  these  poles  which  are  located  in  the 
grey  matter,  and  this  is  an  incontestable  advance  ;  but  the  idea  of  direction  has 
been  sujjplied  by  physiology,  and  can  be  furnished  in  no  other  way. 

2.  Current  of  entry,  current  of  exit.  —  Hence,  in  the  altogether 
similar  fibres  of  these  two  parallel  nerve  trunks  (posterior  and  anterior 
root)  impulses  circulate,  of  which  some  represent  a  current  ivhich  enters 
the  nervous  system  and  others  a  current  which  leaves  it.  The  more  special 
nervous  phenomena  (psychical  phenomena  or  those  of  sensation)  mani- 
fest themselves  in  the  interval  ;  that  is  to  say,  in  the  complicated  net- 
work which  the  elements  of  the  spinal  cord  and  brain  form  between 
them.  Visible  movement  is  external,  in  the  muscles  or  analogous 
organs. 

Order  of  succession  of  the  two  phenomena,  sensory  and  motor.  —  In 
the  nervous  process  regarded  as  a  whole,  movement  ensues  after  sensa- 
tion, of  which  it  is  the  visible  consequence.  This  general  current  of 
cyclic  form,  which  commences  in  the  organs  of  sense  and  finishes  in  the 
muscles,  is  never  inverted.  I7i  the  nervous  system,  as  in  the  vascular 
system,  circulation  is  effected  in  a  definite  direction.  Temporary  checks 
may  occur,  or  different  routes  may  be  followed,  but  it  never  returns 
on  itself. 

Abbreviated  image  of  the  whole  cycle. — If  it  is  desired  to  observe 
this  cyclic  process  in  its  totality,  it  is  only  necessary  to  repeat  the 
experiment  in  different  conditions  :  between  the  posterior  and  the 
anterior  root  only  the  corresponding  segment  of  spinal  cord  is  left,  by 
cutting  the  latter  above  the  lumbar  region,  in  such  a  manner  as  only 
to  permit  reflex  action.  When  limited  in  this  way,  the  complexity  of 
the   phenomenon   disappears,  and  only  the  most  obvious  details  are 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    129 


observed  ;   but,  on  the  other  hand,  it  is  possible  to  ascertain  the  direc- 
tion which  it  follows  in  the  nervous  system. 

Comparative  Physiology. — Batrachia. — Fodera  and  J.  INIviller,  have  extended 
the  discovery  of  Magendie  to  cold-blooded  animals.  The  frog,  on  account  of  the 
shortness  of  its  spinal  cord  and  the  relative  length  of  its  lumbar  roots,  is  one  of 
the  animals  best  adapted  for  every  land  of  experiment  on  the  nerve  roots. 

Birds. — The  fact  has  been  verified  as  regards  birds  by  Schiff,  and  more  especi- 
ally by  A.  Moreau. 

Fishes.  —  A.  Moreau  has  also 
proved  it  as  regards  fishes,  making 
use  of  the  ray,  the  torpedo,  etc., 
species  in  which  the  roots,  after 
their  reunion  in  the  ganglion,  re- 
main easily  separable  for  a  certain 
length  before  forming  a  mixed  nerve. 

Invertebrata. — It  has  been  en- 
deavoured to  ascertain  if  the  in- 
vertebrata present  an  analogous 
dissociation  of  the  nerves  of  sensa- 
tion and  of  movement  at  the  spot 
where  the  peripheral  nerves  leave 
the  ganglionic  chain,  which  in  them 
represents  the  spinal  cord. 

Newjaort,  Longet,  Faivre,  Vulpian 
have  endeavoured  to  ascertain  this, 
the  first  by  dissections,  the  others 
by  cutting  experiments  and  excita- 
tion of  these  nerves  laid  bare  in 
animals  such  as  the  lobster,  crayfish, 
etc.  It  has  not  been  possible  to 
demonstrate  that  in  these  animals 
the  sensory  and  motor  elements  are 
grouped  in  distinct  bundles,  as  in 
the  vertebrata.  According  to  Vul- 
pian, the  elements  of  the  two  orders 
must  be  mixed,  inasmuch  as  all  the 
nerves  which  may  simulate  roots 
give  rise  to  manifestations  both  of 
sensation  and  of  movement. 

No  absolute  distinction  be- 
tween sensation  and  motion. — 
The  experiment  of  Magendie 
therefore  shows,  in  a  very 
clear    manner,    the   distinction 

between  sensation  and  motion.  But  how  must  it  be  interpreted  ? 
Is  it  to  be  assumed  that  there  is  an  absolute  locahzation  within  definite 
boundaries  ;  or  rather,  the  two  phenomena  being  everywhere  closely 
associated,  is  it  merely  that  there  is  an  exaggeration  of  one  or  of  the 
other  in  special  organs  ?     This  last  is  the  true  interpretation. 

P.  K 


Fig.   51. — Diagram  representing  the  medul- 
lary roots  in  the  frog. 

S,  sacrum  represented  in  dots.  Above  it  and 
also  in  dots  are  shown  the  limits  of  the  vertebrae 
between  which  the  nerve  pairs  find  an  egress  by 
the  intervertebral  foramen,  after  a  more  or  less 
oblique  course.  The  spinal  cord  is  much  shorter 
than  the  vertebral  canal  which  terminates  at  the 
base  of  the  sacrum. 

I  to  X,  spinal  nerve  pairs,  whose  posterior  root 
and  gangUon  may  be  observed  in  the  spinal 
canal,  and  the  mixed  trunk  outside  it. 


]30  SYSTEMATIC    FUNCTIONS 

Motion  concealed  under  the  sensory  phenomenon. — And  first  of  all,  as 
concerns  sensation,  it  is  only  in  an  abstract  manner  that  we  can  regard 
it  apart  from  movement.  Not  only,  indeed,  does  it  take  origin  from 
a  movement  (exciting  impulse  on  the  posterior  roots),  but,  throughout 
its  development  in  the  deep  masses  of  the  nervous  system,  it  is  accom- 
panied b}^  a  movement,  invisible,  molecular,  but  not  the  less  real. 
The  importance  of  this  movement  does  not  consist  in  its  quantity, 
which  is  infinitesimal,  but  in  its  complexity,  which  is  extreme  ;  it  is 
the  co-ordination  and  the  synthesis  of  its  component  elements  which 
give  it  its  unity.  And  it  is  this  which  makes  it  absurd  to  seek  for  the 
mechanical  equivalent  of  sensation.  Thus,  in  stimulation  of  the 
posterior  root,  the  phenomenon  of  sensation  is  so  evident,  so  marked, 
that  it  arrests  our  whole  attention  ;  but  it  must  not  prevent  us  from 
recognizing  the  phenomenon  of  motion,  on  which  it  is  superposed,  and 
which  indeed  presides  over  it. 

Sensation  disguised  under  the  motor  phenomenon. — Conversely 
when  movement  is  induced  in  the  muscles  through  excitation  of  the 
anterior  root,  every  trace  of  sensation  seems  to  be  absent  in  this  organ 
and  in  the  motor  nerve  ;  yet  both  are  composed  of  excitable  elements, 
that  is  to  say,  of  elements  possessing  the  earliest  germ  of  sensibility  ; 
so  that  here  also,  under  a  more  marked  phenomenon,  this  time  motion, 
we  must  suspect  another,  latent  and  concealed,  which  is  in  this  case 
sensation.  Both  phenomena  are  present  in  every  living  portion  of 
the  body.  But  that  which  makes  sensation  evident  is  obviously  or- 
ganization, the  synthesis  of  living  elements  into  a  co-ordinated  system. 
That  which  degrades  sensation  and  reduces  it  to  its  simplest  expression 
is  the  dislocation  of  the  system,  its  reduction  to  its  simple  elements 
in  which  movement  alone  seems  to  be  present,  as  in  non-organized 
matter. 

This  is  the  reason  why  the  stimulation  of  the  two  roots  of  the 
nervous  system  (anterior  and  posterior  root)  has  such  different  effects. 
Individually  considered,  they  have  the  same  mutual  value  as  any  other 
tract  of  the  brain  or  spinal  cord,  but  one  is  at  the  entrance  to  the 
system,  and  its  stimulation  extended  over  the  whole  of  this  system 
will  elicit  the  most  remarkable  of  its  manifestations  ;  the  other  is  at 
its  exit  and,  as  such,  can  only  manifest  the  properties  of  the  isolated 
element  which  it  governs  :  the  one  takes  part  in  a  synthetic,  the  other 
in  an  analytic  phenomenon. 

3.  Functional  bonds  of  union. — The  nerve  roots  display  distinct 
functions,  but  these  functions  are  not  independent.  The  connexion 
which  exists  between  sensation  and  motion  is  manifest,  so  far  as  it  has 
been  investigated,  in  all  the  experiments  made  on  these  roots. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS     131 

Influence  of  the  posterior  roots  on  the  excitability  of  the  anterior 
roots. — Harless,  Cyon,  Dastre  and  Marcacci  have  observed  that,  after 
section  of  a  posterior  root,  the  excitability  of  the  corresponding  anterior 
root  (by  an  induced  current)  is  modified.  The  first  of  these  authors 
has  observed  it  to  be  diminished,  the  others,  on  the  contrary,  to  be 
increased.  Belmondo  and  Oddi.  investigating  the  cause  of  these  varia- 
tions, think  that  it  Hes  in  the  fact  that  the  section  of  the  posterior  root 
acted  for  a  certain  time  as  a  more  or  less  persisting  irritation,  before 
suppressing  the  propagation  of  the  impulses  which  are  transmitted  by 
it  as  they  come  from  the  periphery.  In  order  to  overcome  the  irritat- 
ing action  of  mechanical  section,  they  cocainized  the  root  in  which 
they  wished  to  suppress  this  phenomenon,  and  they  then  found  that 
the  excitabihty  of  the  anterior  root  is  always  lowered  after  its  physio- 
logical interruption. 

According  to  these  facts,  it  would  appear  that,  in  addition  to  more 
or  less  lively  accidental  stimulations  which  are  furnished  it,  the  pos- 
terior root  is  the  seat  of  a  sort  of  shght  but  constant  flow  of  impulses, 
which  proceed  to  the  spinal  cord  and  thence  to  the  motor  roots.  \Mien 
the  diastaltic  system  is  not  interrupted  in  any  point  of  its  course  and 
the  anterior  root  is  stimulated  in  its  course,  this  impulse  is  added  to 
those  which  are  already  circulating  in  it,  and  the  effect  of  it  is  then 
greater,  if,  the  posterior  root  being  cut,  this  circulation  should  be  from 
this  fact  interrupted.  Hence  the  sensory  nerve  is  in  a  constant  state 
of  tonic  stimulation,  a  condition  similar  to  that  which  is  known  to 
exist  in  the  muscle,  and  of  which  it  is  the  exciting  cause.  \Yhen  a 
strong  excitation  arises,  and  visible  movement  is  produced,  this  tension 
is  exaggerated  ;  when  every  route  available  to  the  impulse  is  cut,  this 
same  tension  disappears,  and  the  tone  is  said  to  cease.  The  source  of 
tone  is,  in  fact,  this  permanent  current  of  impulses,  the  latter  being 
slight  and  imperceptible. 

Influence  of  the  posterior  roots  on  motor  functions. — When  only  a 
posterior  root  is  cut,  its  suppression  does  not  act  in  a  very  obvious 
manner  on  the  motor  power  of  the  corresponding  anterior  root.  This 
is  so  because  the  grey  matter  of  the  spinal  cord  is  a  locality  in  wliiclj 
a  large  number  of  other  impulses  converge,  both  those  coming  from 
the  uncut  posterior  roots,  and  those  which  have  been  stored  up  in  the 
superior  parts  of  the  nervous  system,  and  which  easily  supplement  the 
deficit  due  to  such  a  limited  lesion.  But  if  a  certain  number  of  sensory 
roots  be  cut,  for  example,  all  those  which  correspond  to  the  posterior 
extremity,  it  is  seen  that  the  movements  of  this  limb,  without  being 
abolished,  are  curiousl}^  disturbed.  CI.  Bernard,  Chauveau,  Tissot  and 
Contejean,  who  have  performed  this  experiment,  point  out  the  inco- 


132  SYSTEMATIC    FUNCTIONS 

ordination  of  the  movements  which  is  the  consequence  of  it.  In  per- 
sons suffering  from  locomotor  ataxy  a  lesion  of  this  nature,  affecting 
the  inter-medullary  prolongations  of  the  posterior  roots,  gives  rise  to 
that  inco-ordination  of  movement  which  is  so  obvious  in  their  mode 
of  progression.  And  it  has  been  proved  that  there  is  an  entirely  sen- 
sory form  of  locomotor  ataxy,  which  is  the  result  of  an  alteration  of 
the  sensory  nerves  (polyneuritis),  apart  from  any  affection  of  the  spinal 
cord. 

2.  Organic  Complications ;   Recurrent  Sensibility. 

The  very  obvious  distinction  which  exists  between  the  nerves  of 
sensation  and  of  motion,  in  the  posterior  roots,  presents,  nevertheless, 
a  paradox,  which  for  a  long  time  compromised  the  law  so  clearly  enunci- 
ated by  Magendie  concerning  the  functions  of  these  roots,  and  this 
obscurity  existed  until  a  rational  explanation  of  this  paradox  was 
given. 

1.  The  fact  and  its  conditions. — The  roots  being  laid  bare,  if,  before 
cutting  them  the  posterior  root  be  pinched,  it  is  found  to  be  very  sensi- 
tive ;  but  if  the  anterior  root  be  pinched  it  will  be  found  to  be  equally 
sensitive.  The  fact  was  in  the  first  instance  observed  by  Magendie, 
was  successively  accepted  and  denied  by  Longet  (1840-1841),  then 
re-discovered  by  CI.  Bernard,  who  propounded  the  conditions  which 
give  rise  to  it.  In  order  the  better  to  observe  it,  it  is  necessary  to  wait 
until  the  animal  shall  have  recovered  from  the  operative  shock  by  a 
suflficiently  long  repose.  The  logical  solution  of  the  paradox  is  due  to 
Longet.  The  sensory  elements  contained  in  the  anterior  root  do  not 
arise  from  the  origins  of  this  root,  but  are  nothing  else  but  elements  of 
the  posterior  root,  which,  instead  of  going  to  the  skin,  re-ascend  into 
the  anterior  root  by  a  re-current  course,  in  order  to  confer  sensation 
on  the  membranes  which  envelop  the  sjjinal  cord. 

Analysis  of  the  phenomenon. — //,  indeed,  the  anterior  root  be  cut  and 
the  two  ends  be  investigated,  the  inferior  will  be  found  to  be  sensory  (as 
also  motor)  and  not  the  superior,  irritation  of  which  gives  rise  to  no 
kind  of  result.  //  the  corresponding  posterior  root  be  cut,  all  sensation 
disappears  from  the  anterior  root,  whether  cut  or  not.  Sensation  in  the 
anterior  root  is,  then,  clearly  a  borrowed  sensation  ;  the  anterior  root 
is  only  a  place  of  passage  for  sensor^'  fibres  which  go  to  the  membranes 
either  of  the  cord,  or  of  these  roots  themselves.  Hence  the  paradox 
is  explained  ;  so-called  recurrent  sensibility  is  nothing  more  than  a  special 
case  of  general  sensation.  The  apparent  exception  to  Magendie's  law 
is  included  in  this  same  rule  and  fully  confirms  it. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    133 

Anatomical  proof. — If,  in  reality,  sensorj-  fibres  which  have  their  trophic 
centres  in  the  cells  of  the  vertebral  ganglion,  enter  by  recui-rence  into  the 
anterior  root,  it  is  possible  to  make  them  evident  by  the  method  of  Wallerian 
degeneration.  By  cutting  the  anterior  root,  these  fibres  are  cut  at  the  same  time 
as  those  incomparably  more  nmnerous  fibres  (motor  fibres)  which  have  their 
trophic  cells  in  the  anterior  cornua  of  the  spinal  cord.  Both  will  degenerate,  but 
in  opposite  dii-ections,  some  in  one  of  the  two  ends  of  the  cut  root,  the  rest  in 
the  other,  and  they  will  in  tliis  way  be  recognizable,  the  degenerated  fibres  sur- 
rounded by  healtliy  ones,  the  healthy  ones  by  degenerated.  And  this,  as  a 
matter  of  fact,  is  what  happens  :  the  medullar^'  end  of  the  anterior  root  which 
has  been  cut  contains  some  degenerated  fibres  amongst  its  healthy  ones,  and 
the  peripheral  end  some  healthy  fibres  among  the  mass  of  degenerated  motor 
fibres.  The  fibres  which  are  present  in  small  number,  and  which  have  an  orien- 
tation contrary  to  the  others,  are  clearly  the  sensory  recm-rent  fibres.  This 
experiment  was  first  made  by  Schiff  on  the  roots  (1850).  Philippeaux  and 
Vulpian  have  repeated  it  on  the  hyj50glossal  and  facial  nerves. 

Arloing  and  Tripier  also  made  use  of  this  method  of  control  when  they  investi- 
gated the  question  of  recurrent  sensibility  under  a  new  asjDect. 

2.  The  reason. — It  is  surprising  at  the  first  glance  that  sensory  ele- 
ments should  be  present  in  membranes  such  as  those  which  cover  the 
spinal  cord  or  the  coverings  of  the  nerve  trunks  ;  because,  as  a  matter 
of  fact,  these  membranes  are  generally  found  to  be  insensitive  when 
experimented  upon,  and  in  theory,  the  only  membranes  which  would 
seem  to  require  sensibility  are  those  which  face  the  exterior,  such  as 
the  skin  or  the  mucous  membrane. 

But  sensation  is  not  necessary  for  us  only  in  our  relations  with  the 
external  world,  it  is  indispensable  as  regards  the  relationship  of  all  our 
organs  to  one  another,  of  all  our  cells  between  themselves  ;  it  is  the 
great  regulator  of  function.  Only  this  sensation  is  not  conscious  in 
the  personal  sense  of  the  word  ;  and  yet  it  may  become  so  as  the  result 
of  changes  due  to  traumatism,  in  the  deep  portions  of  the  organism. 
This  is  one  of  the  reasons  which  cause  it  to  appear  (by  rendering  it 
obscurely  conscious  or  sub-conscious)  in  the  dura  mater  and  the  roots 
a  certain  time  after  the  opening  of  the  spinal  column  after  the  animal 
has  had  time  to  recover  the  shock  of  the  first  operation. 

As  regards  the  cranial  dura  mater,  it  has  been  found  that  filaments 
are  given  off  by  the  trigeminal  nerve,  and  this  membrane  was  known  to 
be  sensitive  by  former  observers.  It  possesses  great  numbers  of  nerve 
fibres,  and  these  latter  are  furnished  with  receptive  apparatus  analo- 
gous to  those  of  touch  or  of  general  sensation. 

Site  of  the  recurrence. — The  recurrence  of  the  fibres  which,  from 
the  posterior  become  involved  in  the  anterior  root,  is  not  carried  out 
at  the  union  of  the  two  roots,  in  the  mixed  trunk  which  is  the  result 
of  this  union  ;  it  is  effected  much  farther  away,  in  the  plexus  which 
arises  from  the  combination  of  these  trunks.     Section  of  the  mixed 


134  SYSTEMATIC    FUNCTIONS 

trunk  in  the  neighbourhood  of  the  roots  abohshes  sensation  in  the 
anterior  root,  just  as  if  the  posterior  root  had  itself  been  cut  (CI. 
Bernard). 

CI.  Bernard  maintains  that  every  anterior  root  acquires  its  recurrent  sensi- 
bility from  the  corresponding  posterior  root,  and  iiot  from  another.  According 
to  him,  this  correspondence  would  be  one  of  the  characteristics  of  the  physio- 
logical nerve  pair  ;  he  employs  it  more  particularly  in  the  study  of  the  bulbar 
nerves  in  order  to  determine  the  sensory  and  motor  elements  which  form  the 
functionally  active  cranial  pairs.  It  is  possible  that  this  character  may  have 
some  importance,  but  it  is  not  absolute.  Recvirrence  may  be  met  with  not  only 
from  sensory  nerve  to  iTiotor  nerve,  but  from  sensory  nerve  to  sensory  nerve 
(Arloing  and  Tripier). 

3.  Generalization  of  the  fact. — Through  the  labours  of  Arloing  and 
Tripier,  the  question  of  recurrent  sensibility  has  been  at  the  same  time 
extended  and  renewed.  Recurrence  of  sensory  fibres  is  not  a  fact 
peculiar  to  the  motor  roots,  but  is  much  more  general.  It  is  not  merely 
a  device  to  render  sensitive  the  medullary  or  deep  membranes,  but  it 
occurs  in  the  distribution  of  sensory  nerves  in  the  skin  itself  and  plays 
an  important  part  therein.  The  more  nearly  the  cutaneous  investment 
is  ajjproached,  the  greater  is  the  imj^ortance  and  the  extension  of  this 
recurrence.  It  here  presents  also  a  ncAV  character  :  instead  of  being 
confined  to  the  area  of  a  nerve  trunk,  it  mixes  the  extremities  of  the 
sensory  fibres  over  a  more  or  less  extended  surface. 

Experiment. — One  of  the  most  striking  experiments  of  these  authors 
is  the  following  :   in  a  dog  the  four  collateral  nerves  (the  two  palmar 
and  the  two  dorsal)  of  one  of  the  digits  of  an  extremity  are  uncovered. 
These  nerves  are  successively  cut,  and  after  each  section  the  sensation 
of  the  digit  is  investigated.     After  section  of  the  first,  of  the  second 
and  of  the  third,  sensation  is  found  to  be  dulled,  but  the  digit  does  not 
present  any  area  which  is  completely  anaesthetic.      But  if  the  fourth 
nerve  be  cut,  the  whole  digit  becomes  completely  insensible.     The 
conclusion  to  be  drawn  from  this  experiment  is  that  the  four  collateral 
nerves  have  not  individually  an  area  of  distribution,  but  that  they 
interchange  their  fibres  by  means  of  the  terminal  anastomoses  which 
anatomy  proves  to  exist  between  them.     These  anastomoses  are  the 
result  of  recurrence  ;  for,  after  section  of  one  of  the  nerves,  the  method 
of  degenerations  invariably  shows  the  presence  of  a  small  number  of 
degenerated  fibres  surrounded  by  healthy  fibres  of   the   central  end, 
and  conversely. 

Applications. — These  facts,  well  established  both  anatomically  and  physio- 
logically, supply  a  plaxisible  explanation  of  persistence,  or  of  rapid  return  of 
sensation,  after  section  of  more  or  less  important  nerve  trunks  (median  nerve), 
consecutive  to  nervous  suture,  as  well  as  in  the  absence  of  the  latter.     The 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    135 

re-establislament  of  sensation  is  probably  due  to  the  fact  that  the  apparent 
area  of  distribution  of  the  cut  nerve  is  invaded  by  fibres  of  neighbouring 
nerve  trunks,  thanks  to  the  recurrent  anastomoses  which  are  so  numerous  at 
the  peripliery. 

4.  Recurrent  motricity. — The  same  reasons  which  cause  certain 
fibres  of  the  posterior  roots  to  re-ascend  in  the  anterior  roots,  in  order 
to  supply  sensation  to  the  corresponding  meduhary  area,  should  also 
cause  certain  fibres  of  the  anterior  roots  to  re-ascend  in  the  posterior 
roots,  in  order  to  supply  motor  power  to  the  organs  of  movement  which 
are  present  in  the  interior  and  at  the  surface  of  the  spinal  cord.  Just 
as  sensation,  so  is  movement  everywhere,  under  a  visible  or  invisible, 
mechanical  or  molecular  form.  Visible  movement  occurs  in  the  spinal 
cord  (as  in  the  brain),  since  it  contains  (as  does  the  latter)  contractile 
vessels  to  which  vaso-motor  fibres  are  supphed.  Independently  of 
the  invisible  movements,  there  are  intrinsic  activities  in  the  fixed  cells 
of  its  membranes,  exchanges  with  the  surrounding  blood  which  imply 
stimulation  and  a  direction  imposed  by  the  motor  portion  of  the  ner- 
vous system. 

Remark. — Sensory  and  motor  elements  thus  arise  from  the  spinal  cord,  and, 
after  a  more  or  less  lengthy  course  outside  the  latter,  they  return  to  it,  having 
their  point  of  termination  (or  being  able  to  have  it)  quite  close  to  their  point  of 
departure.  The  centre  and  the  periphery  are  thus  united  in  the  same  organ,  and 
this  organ  is  the  spinal  cord.  Nothing  more  clearly  renders  evident  the  fact  that 
these  expressions,  centre  and  periphery,  have  merely  a  relative  and  conventional 
value.  It  is  important  to  remember,  indeed,  that  the  two  words  are  used  some- 
times in  an  anatomical  and  concrete  sense,  sometimes,  on  the  other  hand,  in  a 
metaphorical  and  abstract  sense.  In  a  differentiated  system,  such  as  is  the 
animal  organism,  every  organ,  every  constituent  part  is,  in  virtue  of  its  differen- 
tiation into  a  given  order  of  functions,  a  centre  for  other  parts,  which  we  then 
call  the  periphery,  for  want  of  a  better  word  ;    and  reciprocally. 

The  prolonged  course  of  these  fibres,  which  leave  the  spinal  cord  in  order  to 
return  to  it,  seems  contrary  to  the  arrangement  which  governs  the  living  organi- 
zation ;  but  this  course  is  rendered  necessary  by  a  reason  which  is  of  embryo- 
logical  natiu-e.  The  origin  of  the  sensory  fibres  is  in  the  spinal  ganglia,  that  of 
the  involuntary  motor  fibres  is  in  the  great  sympathetic  ganglia  :  it  is  necessary 
that  they  pass  tlirough  these  ganglionic  masses,  wherever  they  come  from  or 
whither  they  go. 

Vulpian  has  investigated  tMs  recm-rent  motricity  by  exciting  the  peripheral 
end  of  an  anterior  root  while  observing  the  state  of  the  cii'culation  at  the  surface 
of  the  spinal  cord  in  its  corresponding  segment.  He  has  not  noticed  any  change. 
But  it  is  possible  that  the  vaso-motors  of  the  sjainal  cord,  like  those  of  the  brain, 
have  in  the  sympathetic  chain  a  more  or  less  considerably  prolonged  course,  the 
result  of  which  is  that,  leaving  by  an  anterior  root  (or  even  a  posterior  root)  of 
the  dorsal  region,  for  example,  they  re-enter  the  spinal  cord  by  a  posterior  root 
(or  even  an  anterior  root)  of  another  region  situated  above  or  below. 

Decisive  experiment. — When  the  sympathetic  is  stimulated  in  the  neck  and 
when,  as  has  been  observed  by  several  authors,  changes  are  noticed  in  the  vas- 
cular supply  of  the  brain  (dura  mater  or  cerebral  substance),  it  is  a  question, 


136  SYSTEMATIC    FUNCTIONS 

fundamentally,  of  a  motor  recurrent  jjhenomenon.  Having  started  from  a 
nerve  centre,  which  is  here  the  spinal  cord  (which  may  receive  it  from  the  brain), 
the  motor  impulse  has  returned  in  the  interior  of  a  nerve  centre  (the  brain)  to 
the  motor  elements  which  the  latter  contains  ;  there  can  be  no  doubt  that  it 
returns  in  a  similar  way  to  the  vessels  of  the  spinal  cord,  by  routes  which  remain 
to  be  exactly  defined. 


3.  Conventional  Definitions  ;  The  Sensory  and  Motor  Field 

The  posterior  root  is  called  sensory,  not  that  it  exactly  feels,  but 
because  it  arouses  sensation  in  a  system  which  follows  it  ;  the  anterior 
root  is  called  motor,  not  because  it  moves,  but  because  it  gives  rise  to 
a  movement  in  the  organs  situated  at  its  extremity.  What  are  the 
exact  hmits  of  the  sensory  system,  and  where  does  the  motor  system 
commence  ?  Formerly  it  was  maintained  that  in  the  spinal  cord, 
and  afterwards  in  the  brain,  was  situated  a  posterior  area,  sensory  in 
function,  and  an  anterior  area,  motor  in  function  ;  both,  in  a  way,  being 
a  continuation  of  the  roots,  which  were  prolonged  without  any  great 
alteration  as  far  as  to  the  two  extremities.  But  the  data  furnished 
both  by  anatomy  and  by  physiological  experiments  in  no  way  con- 
firm such  a  supposition. 

1.  Comparison  of  the  posterior  and  anterior  portions  of  the  spinal 
cord  and  of  the  brain. — So  far  as  concerns  the  spinal  cord,  sensation 
may  be  aroused  if  certain  tracts  are  irritated,  and  as  the  result  of  irrita- 
tion of  certain  other  tracts  movements  may  ensue  ;  yet  these  pheno- 
mena are  far  from  reproducing  quantitatively  and  qualitatively  those 
which  are  due  to  stimulation  of  the  roots.  As  concerns  the  cerebral 
cortex,  the  sensory  and  motor  areas,  instead  of  being  disposed  in 
different  departments,  seem  to  be  superposed,  which  would  appear  to 
confirm  the  view  of  a  cyclic  process  substituted  for  that  of  an  isolated 
locahzation  of  sensation  and  motion. 

Indefinite  limits  of  sensation  and  of  motion. — It  is  consequently 
impossible  to  point  out  exactly  where  sensation  ceases  and  motion 
commences,  the  passage  from  one  to  the  other  being  gradual.  All  that 
can  be  said  is  that,  from  the  mgans  of  the  senses  to  the  brain  the  develop- 
ment of  the  psychical  phenomenon  of  sensation  is  progressive  ;  ivhile 
from  the  brain  to  the  muscles  it  follotvs  a  retrograde  course,  ending  by 
external  movement.  The  former  of  these  roots  are  ascending,  and  the 
custom  of  calling  them  sensory  has  become  widespread  :  the  others 
are  descending ;  they  are  generally  called  motor.  At  the  present  day 
it  would  be  impossible  to  change  these  names  for  any  better  adapted 
for  the  purpose  ;  but  it  must  be  remembered  that  they  have  but  a 
conventional  value,  and  that  the    difference  of   function  which  they 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    137 

indicate  progressively  diminishes  in  proportion  as  we  approach  more 
nearly  to  the  cerebral  cortex. 

With  regard  to  the  impulses  which  it  receives,  the  nervous  system 
first  acts  as  a  distributing  agent,  in  its  superior  regions  so  singularly 
called  centres,  later  as  a  concentrating  one  upon  the  organs  of  move- 
ment. 

The  old  criteria. — The  cause  is  easily  recognized  which  at  first  embarrassed 
authors  in  their  efforts  to  define  and  classify  the  fimctions  of  the  spinal  cord  and 
brain,  and  above  all  of  the  cerebral  cortex.  They  were  convinced  that  motion 
excluded  sensation,  and  that,  reciprocally,  sensation  excluded  motion.  As  a 
matter  of  fact,  these  two  functions  are  on  the  contrary  confovmded  and  inex- 
tricably mixed.  According  then  as  one  or  other  of  these  two  phenomena  chiefly 
attracted  then*  attention  in  some  nervous  assemblage,  they  elected  either  for 
sensation  or  motion.  When,  for  example,  with  Schiff  and  rran9ois-Franck, 
the  surface  of  the  brain  is  compared  to  a  sensitive  siu-face,  like  the  skin,  the 
analogy  is  very  true  from  the  pi^irely  experimental  point  of  view,  but  from  tliis 
point  of  view  only,  because  it  deals  with  a  very  special  case,  that,  namely,  in  which 
the  cerebral  cortex  being  put  out  of  action  as  an  apjDaratus  capable  of  transform- 
ing the  impulse,  this  latter  need  be  only  reflected  to  the  spinal  cord  in  order  to 
reach  the  motor  organs  properly  so  called.  But  if,  the  cortex  being  intact,  the 
impulse  arising  from  the  skin  passes  through  the  latter,  new  characters  are 
imposed  on  it  by  reason  of  this  transit,  and  these  markedly  svu-pass  those 
which  are  acquii'ed  in  the  spinal  cord. 

In  the  double  jom-ney  which  it  makes,  the  one  ascending  (from  the  spinal  cord 
to  the  brain),  the  other  descending  (from  the  brain  to  the  spinal  cord),  the  un- 
pulse  proceeds  from  reflection  to  reflection,  or,  better,  from  transformation  to 
transformation  ;  but  these  transformations  have  very  unequal  values  in  the 
spinal  cord  and  in  the  brain.  When  the  impulse  proceeds  from  the  fu-st  of  these 
organs  to  the  second,  the  sensory  character  predominates,  as  is  proved  by  the 
absorption  of  the  impulses  wliich  ensues  in  the  brain  without  any  motor  effect 
resulting  ;  when  the  impulse  descends  from  the  second  to  the  first,  the  motor 
character  is  that  which  predominates,  yet  it  cannot  be  said  that  it  is  entirely 
dissociated  from  sensation,  inasmvich  as  it  recalls  the  latter  in  its  inferior  degrees. 

For  the  absolute  meaning  that  these  two  words  "  sensation  "  and  "  motion  " 
have  up  to  now  preserved,  it  is  necessary  to  substitute  a  relative  one,  which  alone 
corresponds  to  the  real  state  of  affairs  ;  for  the  opposition  which  they  expressed 
a  gradation  must  be  substituted,  a  progression  which  connects  them  the  one  with 
the  other  ;  but  as,  in  the  absence  of  expressions  which  indicate  the  different 
values  of  this  gradation,  the  old  terms  are  indispensable,  we  shall  describe  by 
the  term  sensory  field  all  that  part  of  the  nervous  system  in  which  sensory  char- 
acters predominate  over  those  which  are  motor,  and  motor  field  all  that  region 
in  which  motion  predominates  over  sensation.  Arbitrary  as  it  is,  this  definition 
is  founded  on  fact. 

Sensory  and  voluntary  excitation. — Our  own  powers  of  observation  show  us 
that  sensation  may  exist  in  us  independently  of  muscular  movement,  and  they 
further  tell  us  that  movement  may  originate  in  us  in  an  apparently  spontaneous 
fashion  under  the  influence  of  certain  determining  factors  which  we  call  volun- 
tary. In  interpreting  these  two  facts,  it  seems  to  have  been  often  thought  that 
sensation  is  localized  at  the  termination  of  the  ascending  conductors,  and  the 
will  at  the  origin  of  the  descending  conductors,  just  as  if  a  plane  of  division  existed 
between  these  two  wliich  could  be  clearly  defined  in  the  nervous  system.  In 
reality  the  arrangement  is  by  no  means  so  simple. 


138 


SYSTEMATIC    FUNCTIONS 


(1)  When  an  actual  sensory  impulse  is  only  reflected  on  the  muscles,  we  have 
no  reason   to  believe  that  it  is  stopped  at  the  ideal   plane  which  has  just  been 


("  Ruban  de  Reil' 


Fillet 


Cran.  Sensory  N. 
Sens,  decussation. 


N.  of  Goll  and  of 
Burdach. 


Column  of  GoU. 


Anterior  column. 


Lateral  column. 


Ant.  commtss. 


Post.  corn. 


Spinal  If. 


Fig.   52. — Sensory  field  with  its  two  chief  orders  of  fibres  of  projectioru 


referred  to  ;    on  the  contrary,  we  have  cause  to  think  that  it  often  goes  beyond 
this  boundary.     If,  indeed,  it  does  not  produce  immediate  movement,  it  usually 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    139 

produces  a  tendency  to  movement   (sometimes    slight   tension,  of   the  'muscles), 


A.lc^J' 


Fig.   53. — Motor  field,  with  its  two  principal  orders  of  fibres  of  projection. 

arrested  in  its  effects  by  antagonistic  influences  situated  in  the  very  interior  of 
the  nervous  system. 

(2)  When,  on  the  other  hand,  the  muscles  are  put  in  action  by  a  voluntary 


140  SYSTEMATIC    FUNCTIONS 

excitation  we  have  no  reason  to  believe  that  this  latter  arises  in  this  plane  of 
separation,  and  we  are  justified  in  maintaining  that  it  proceeds  from  the  nervous 
conductors  which  precede  it.  It  arises,  in  fact,  from  a  memory  which  is  equivalent 
to  a  resuscitation  of  anterior  sensory  excitations. 

In  the  first  case,  the  imjDulse,  after  having  traversed  the  ascending  paths,  is 
extinguished  in  the  course  of  the  descending  paths,  without  reacliing  the  muscles  : 
its  effect  is  not  lost,  but  it  is  postponed. 

In  the  second  case  the  impulse,  which  traverses  the  descending  paths  in  order 
to  reach  the  muscles,  still  proceeds  from  the  ascending  roots,  but  not  from  their 
origin  in  the  organs  of  sense.  It  pays  the  arrears  of  anterior  excitations  kept 
in  reserve  in  the  nervous  system,  esj^ecially  in  the  brain. 

In  the  two  cases  the  exciting  cycle  is  formed  in  that  jaart  of  the  nervous  arc 
which  is  called  superior,  that  which  gives  to  the  phenomena  of  innervation  their 
jDsychical  value,  and  which  is  localized  in  the  brain,  although  no  precise  limits 
can  be  assigned  to  it. 

Is  not  the  process  which  maintains  the  impulse  in  the  brain  in  a  condition 
which  may  be  described  as  potential  itself  of  a  cyclic  nature,  intended  to  store  it 
up  and  causing  it  to  reappear  in  an  automatic  and  unconscious  fashion  ?  We 
may  certainly  ask  this  question,  considering  the  generality  of  the  process  and 
the  slight  expenditiu-e  of  energy  which  nerve  actions  require.  But  the  verifica- 
tion of  such  a  hypothesis  is  so  far  incajoable  of  being  effected  experimentally. 

Double  difficulty. — The  difificulty  wliich  attends  the  analysis  of  the  functions 
of  the  spinal  cord  and  brain  is  double.  The  first  arises  from  the  fact  that  the 
motor  and  sensory  characters,  which  are  so  clearly  recognizable  at  the  two  ex- 
tremities of  the  cycle,  gradually  change  in  proceeding  from  its  origin  to  its  termi- 
nation. The  second  is  due  to  the  fact  that  the  nerve  elements  which  represent 
these  functions  more  or  less  modified,  instead  of  remaining  separate  one  from 
the  other  by  forming  distinct  bundles  as  in  the  roots,  are  often  intermixed,  fibre 
by  fibre.     Further,  this  intermixture  begins  in  the  roots  themselves. 


2.  Mixture  of  the  sensory  and  motor  elements  from  the  medullary 
roots. — The  distinction  of  the  peripheral  elements  of  the  nervous 
system  into  two  classes,  of  which  one  carry  the  impulse  into  the 
nervous  system  and  the  others  convey  it  away,  is  an  absolutely  funda- 
mental principle  of  physiology,  and  one  which  has  never  been  con- 
tradicted. Nevertheless,  experiment  does  not  demonstrate  it  in  that 
clear  and  definite  manner  in  which  it  appeared  to  the  first  observers, 
because  these  latter  were  ignorant  of  certain  complications  which  have 
since  their  time  been  revealed  in  the  nervous  organs  (roots)  wliich  they 
regarded  as  simple,  and  these  complications  alter,  as  concerns  its 
anatomical  enunciation,  the  primitive  formula  of  the  law  of  Magendie. 

In  other  words,  the  distinction  of  peripheral  elements  into  centri- 
petal and  centrifugal  is  not  demonstrated  at  the  present  time  by  a 
single  crude  experiment,  but  is  deduced  by  reasoning  which  is  based 
on  a  varied  assemblage  of  experimental  facts. 

Nevertheless,  amidst  these  secondary  facts  the  experiment  of 
Magendie  remains  so  convincing,  that  it  is  customary  to  place  these 
latter  on  one  side,  by  giving  to  the  anatomical  terms  (posterior  and 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS   141 

anterior  roots)  a  symbolical  value  equivalent  to  that  of  centripetal 
and  centrifugal  nerves. 

Structural  complications. — Nerve  trunks  exclusively  formed  of 
identical  elements  do  not  exist  in  the  organism.  The  spinal  nerve 
roots  represent  those  of  these  trunks  which  the  most  closely  approxi- 
mate to  this  simplicity,  but  without,  however,  attaining  it. 

Mixed  functions  of  the  posterior  roots.- — The  posterior  roots,  com- 
posed almost  entirely  of  centripetal  elements,  contain  a  very  minute 
proportion  of  ceyitrijugal  elements.  Anatomy  proves  this  by  its  own 
special  methods.  The  posterior  roots  contain  neurons,  which  have 
the  morphological  character  (polar  orientation)  of  centripetal  elements 
(Lenhosseck,  Cajal).  The  method  of  degeneration  confirms  this.  After 
section  of  the  posterior  roots  some  healthy  fibres  are  found  amidst 
those  which  are  degenerated  in  the  medullary  end,  and  in  the  gangh- 
onic  end  some  degenerated  fibres  in  the  midst  of  the  large  number  of 
sensory  fibres  which  are  still  healthy  :    this  proves  that  the  posterior 


Axis-cyl. 


Ant.  fissure. 
Figs.   54  and  54a. — Motor  fibres  of  the  posterior  roots. 

On  the  right,  ch'awing  from  nature  (Van  Gehuchten)  from  the  embryo  of  a  fowl  ;    on  the  left 
diagram.  j 

root  contains  elements  whose  trophic  centre  is  in  the  spinal  cord 
(Morat  and  Bonne). 

3.  Physiological  proofs. — If,  after  having  laid  bare  the  lumbo-sacral 
roots  (in  the  dog),  one  of  them  be  selected  (the  sixth  lumbar,  for 
example),  and  be  cut  in  its  course,  and  if  the  peripheral  end  be  irri- 
tated, it  will  be  observed  that  the  temperature  of  the  corresponding 
hind  limb  rises  considerably  (Strieker,  Gartener). 

If  an  animal  be  chosen  whose  skin  is  not  pigmented,  and  the  colour 
of  the  pulp  of  the  toes  be  examined  after  careful  washing,  it  will  be 
seen  that  this  colour  progressively  darkens  while  the  excitation  con- 
tinues,   the   former   colour   reappearing   when   the    excitation   ceases 


142 


SYSTEMATIC    FUNCTIONS 


(Morat)  ;  this  is  a  proof  that  the  nerve  trunks  contain  a  certain  pro- 
portion of  vaso-dilator  elements.  Section  of  the  posterior  roots  is 
followed,  after  a  certain  time,  by  trophic  disturbances,  such  as 
cutaneous  ulceration,  falling  of  the  nails  and  of  the  hair,  thickening  of 
the  skin  and  of  the  skeleton,  chiefly  at  the  extremity  of  the  limb, 
disturbances  which  are  in  reality  explicable  neither  by  vaso-motor 
changes  nor  by  those  of  sensation  (Morat). 

These  phenomena  are  motor  and  as  such  under  the  domain  of  the 
centrifugal  nerves,  but  their  motricity  is  of  a  special  kind  unknown 
at  the  time  of  Magendie,  when  no  other  motion  was  known  than  that 
which  was  voluntary,  and  at  the  same  time  external  and  evident,  of 
the  muscles  of  the  skeleton. 

Root  elements  of  one  system  mixed  with  the  intercentral  elements 
of  another. — \Mien  applied  to  the  nerve  roots,  the  expressions  posterior 
and  sensitive,  anterior  and  jnotor,  are  precisely  equivalent,  on  one  con- 


Ront  Gangl. 
Post,  root 


Affer.  som.  Fibres 
Root  trunk 

Som.  eff.  F. 
Inter-vert,  nerve 


Eff.  Sp'a.-irh  F. 
Sym.  gangli- 


Aff.  splanch.  F. 


^ 


Fig.   55. — Spinal  nerve  roots,  great  sympathetic,  mixed  nerve. 

Division  between  sensitory   (blue  fibres)  and  motor  (red  fibres). 

After  their  intermixture  at  the  meeting  point  where  the  mixed  nerve  arises,  there  is  a  fresh 
division  between  consciousness  (somatic  fibres)  and  unconsciousness  (splanchnic  or  sympathetic 
fibres). 

Structural  complications  arise  from  the  presence  of  centrifugal  elements  in  the  posterior  roots, 
from  the  presence  of  sensory  recurrent  fibres  in  the  anterior  roots,  from  the  presence  of  recurrent 
sympathetic  fibres  involved  in  tlie  inter-vertebral  nerve,  and  finally  from  sympathetic  fibres 
joining  the  somatic  nerve  (not  indicated). 


dition  :    this  is   that  the  sensation  is  conscious  and  the  movement 
voluntary.     When  it   is   a  question  of  movement  and  sensation   of 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    143 

visceral  organs,  these  expressions  are  no  longer  equivalent.  As  a 
matter  of  fact,  as  will  be  explained  farther  on,  the  medullary  roots 
only  merit  the  name  of  roots  as  regards  a  portion  of  the  nervous 
system,  that,  namely,  which  is  knowTi  as  the  voluntary  conscious  side, 
or  that  of  animal  life  ;  as  regards  another  portion,  which  is  the  in- 
voluntary, unconscious  side,  and  which  is  represented  by  the  great 
sympathetic,  they  are  no  longer  roots,  but  interceniral  fibres,  extend- 
ing from  the  ganglia  of  this  system  to  the  spinal  cord,  which  they 
bring  into  reciprocal  relation  bj^  exchange  of  impulses  ;  and,  being 
such,  they  already  present  those  intricacies  which  render  the  study 
of  the  central  masses  of  the  nervous  system  so  extremely  difficult. 

Spinal  roots  or  those  of  the  conscious  voluntary  system,  and 
ganglionic  roots,  or  those  of  the  unconscious  involuntary  system. — 
The  roots  of  the  great  sympathetic  must  not  then  be  sought  for  in 
the  spinal  cord,  but  outside  its  gangha  towards  the  periphery.  It  is 
proved  (more  especially  by  histological  investigations)  that  neurons 
arranged  inversely  place  these  ganglia  in  connexion  with  sensory 
surfaces  and  motor  organs.  Indeed,  these  two  effects  may  be  physio- 
logically dissociated  by  stimulating  comparatively  the  central  and 
peripheral  end  of  a  sympathetic  branch  after  the  latter  has  been  cut  ; 
but,  in  the  sympathetic,  fasciculations  which  effect  an  anatomical 
dissociation  of  these  two  species  of  nerves,  comparable  to  that  of 
the  medullary  roots  of  the  system  of  the  life  of  relation,  are  nowhere 
to  be  found. 

B.  SPINAL  NERVES.  METAMERISM 
The  repetition  of  the  roots  of  the  nerves,  which  are  arranged  in 
graduated  order  throughout  the  length  of  the  spinal  cord,  with 
identical  characters  and  connexions,  is  a  fact  which  of  itself  ^vould 
arouse  attention.  When  connected  w^th  the  form  of  the  skeleton  in 
the  adult,  and,  above  all,  with  the  facts  furnished  by  embryology  and 
by  comparative  anatomy,  it  assumes  a  high  degree  of  significance. 
Moquin-Tandon  (1827)  had  termed  zoonites  those  segments  which  are 
so  easy  to  recognize  in  the  external  form  of  many  invertebrate 
animals.  Duges  extended  this  conception  to  all  the  ramifications,  all 
animals  being,  in  the  early  stage  of  their  development,  formed  of 
parts  ranged  in  series,  which,  in  spite  of  their  reciprocal  penetration, 
preserve  the  anatomical,  and  even  functional  traces  of  their  primitive 
separation.  The  metameres  of  the  vertebrate  (Hoekel)  are  nothing 
more  than  the  zoonites  of  the  invertebrata. 

The  segmentation  which,  in  the  adult,  is  rendered  evident  by  the 
repetition  of  the  medullary  roots  and  of  the  ganglia  of  the  great 


144 


SYSTEMATIC    FUNCTIONS 


sympathetic,  is,  in  the  beginning,  much  deeper  ;  it  divides  up  the 
muscles,  the  nerve  axis,  the  skin  itself,  into  distinct  territories  (myo- 
meres, neuromeres,  dermatomeres)  which  correspond  in  each  metamere. 
The  osseous  skeleton,  whose  development  is  slower,  reproduces  this 
arrangement  in  the  spinal  column,  in  which  it  becomes  permanent. 

To  return  to  the  adult  :  if,  starting  from  the  medullary  roots, 
their  tracts  be  followed  either  internally  in  the  spinal  cord  or  ex- 
ternally towards  the  plexuses  and  nerve 
trunks  which  arise  from  them,  the  meta- 
meric  disposition  seems  to  have  more  or 
less  disappeared,  as  the  result  of  the  in- 
tricacy of  the  peripheral  nerve  trunks  and 
of  the  enormous  expansion  of  the  roots 
in  the  medullary  tracts.  For  its  recogni- 
tion it  is  necessary  to  make  use  of  the 
analytical  devices  which  pathology  some- 
times furnishes  in  a  very  perfect  fashion. 

1.  Root  and  spinal  metamerism. — 
Brissaud,  who  has  made  a  special  and  very 
exhaustive  study  of  nervous  metamerism, 
distinguishes  between  a  radicular  meta- 
merism (that  which  is  rendered  evident 
by  the  anatomical  arrangement  of  the 
nerve  roots),  and  a  spinal  or  medullary 
metamerism  (that  which  is  based  on  the 
fact  that  the  segments  of  the  spinal  cord 
correspond  to  the  implantation  of  the 
roots  or  myomeres),  but  he  is  careful  to 
point  out  that  the  one  does  not  in  any 
way  imply  the  other  ;  and  the  reason  of 
this  difference  is  easy  to  comprehend. 
Radicular  metamerism  is  genuine  meta- 
merism :  each  nerve  pair  is  a  perfect 
reproduction  of  the  nerve  pair  situated 
above  and  below  it.  When  followed  to  the  periphery,  the  nerve  pair 
conducts  us  through  territories  (cutaneous  or  muscular)  which  are,  if 
not  entirely  independent,  at  least  clearly  circumscribed  and  capable 
of  being  defined.  On  the  other  hand,  spinal  metamerism  is  a  meta- 
merism which  is  reduced  to  a  mere  trace.  The  primitively  independent 
medullary  segments  (as  regards  phylogenetic  as  much  as  ontogenetic 
evolution)  are  mutually  interpenetrated  by  their  exogenous  elements, 
as  well  as  by  those  which  are  endogenous  and  associating,  in  such  a 


Fig.  56. — Spinal  nerves  in  the 
frog,  and  its  vertebral  cokxmn. 
(front  view). 

NO,  optic  nerve  ,  A,  atlas  ;    I  to 
X,  spinal  nerve  pairs. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    145 

manner  as  to  consolidate  them  for  the  functions  of  the  whole  ;  these 
functions  being  more  extensive,  more  definite,  and  more  perfect,  are 
substituted  for  their  uniform  and  rudimentary  function  ;  and  the 
higher  we  go  in  the  supefposed  structures  of  the  nervous  system,  the 
more  obvious  will  this  be.  The  little  independence  which  is  left  to 
the  myelomeres  is  represented  by  functional  connexions  which  unite, 
the  one  with  the  other,  the  posterior  and  the  anterior  root  of  the  same 
nerve  pair,  for  the  exercise  of  the  most  simple  reflexes.  After  isola- 
tion of  the  medullary  segment  (myelomere),  each  separate  section, 
furnished  with  its  sensory  and  motor  nerves,  can  still,  in  a  manner, 
perform  the  functions  of  a  partially  independent  system.  Apart  from 
these  elementary  acts,  it  is  intimately  consolidated  with  the  others. 

Number  of  Metameres. — In  man  there  are  seven  cervical  jiairs,  twelve  dorsal, 
five  lumbar,  five  sacral,  one  coccygeal. 

In  the  dog,  seven  cervical,  thirteen  or  fourteen  dorsal,  seven  lumbar,  five  sacral, 
several  coccygeal. 

The  spinal  cord  does  not  occupy  the  whole  length  of  the  canal,  whence  arises 
the  existence  of  a  cauda  equina,  as  in  man. 

In  the  bird  there  are  twelve  cervical  pairs,  seven  dorsal,  thirteen  lumbar,  and 
seven  caudal.  The  spinal  cord  occupies  the  whole  length  of  the  canal,  conse- 
quently there  is  no  cauda  equina,  no  fihun  terminale. 

In  the  frog  there  are  ten  spinal  pairs.  The  cord  is  very  short  with  regard  to 
the  spinal  column,  and  ends  in  a  long  filum. 

In  man  and  the  majorit%-  of  animals  the  dm*a  mater  is  separated  from  the  spinal 
cord  by  a  certain  space.  In  the  caniivora,  especially  the  dog,  the  dura  mater 
covers  up  the  cord,  with  which  It  is  in  contact.  These  two  characteristics,  the 
lengtli  of  the  cauda  equina,  and  application  of  the  dvu*a  mater  to  the  spinal  cord, 
with  an  extra-dural  space  filled  with  fat,  greatly  facilitate  section  of  the  vertebra?, 
the  laying  bare  of  the  spinal  cord  and  operations  (section,  stmiulation)  performed 
on  the  roots  in  order  to  determine  their  functions.  In  the  herbivora,  especially 
in  the  rabbit,  these  special  facilities  either  do  not  exist,  or  are  greatly  reduced. 

2.  Radicular,  cutaneous  territories  ;  areas  of  anaesthesia. — If  a 
posterior  root  is  interrupted,  an  anaesthetic  territory  (or  rather  a 
hypo- aesthetic  territory),  whose  situation  and  form  is  determinate, 
will  be  found  in  the  skin.  This  territory  is  the  corresponding  derma- 
tomere. 

In  the  case  of  the  roots  which  run  a  regular  and  non-plexiform 
course,  such  as  the  intercostal  nerves,  it  will  be  easily  understood 
that  this  territory  itself  will  be  regular,  assuming  the  form  of  zones 
or  of  girdles  ;  but  that  it  should  be  the  same  as  regards  the  roots  of 
the  lumbar,  sacral  or  brachial  nerves,  in  spite  of  the  plexuses  which 
collect  them  together,  would  certainly  be  more  unexpected  ;  as  a 
matter  of  fact  this  is  so.  If  it  be  conceived  that  an  individual 
be  placed  in  the  position  of  a  quadruped,  or  rather  that  the  limbs  are 

P.  L 


146 


SYSTEMATIC    FUNCTIONS 


separated  and  perpendicular  to  the  trunk,  the  skin  of  this  individual 
may  be  divided  into  as  many  superposed  zones  as  there  are  nerve 


-  d  J  ■ - 

■■' d's- 

"■ d'f "■ 

ZT"-'  ■  ' 

" d  3 ' 

d^^'^ 

--.    ^  ^^    ..- 

Fio.   57. — Areas  of  radicular  distribution  of  the  spinal  nerves  (after  Kocher). 

Front  view. 

pairs  (at  the  least  the  spinal).      The  dermatomeres  assume  the  form  of 
circular  bands  arranged  in  stages.     As  regards  the  upper  limb,  they 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    147 

are  prolonged  along  its  length  in  parallel  bands,  more  or  less  regularly 
arranged,  but  continuous.!     As  regards  the  lower  limb,  they  are  always 


Fig.   58. — Areas  of  radicular  distribution  of  the  spinal  nerves  (after  Kocher). 

Back  view. 

placed  lengthwise,  but  are  rendered  discontinuous  by  the  blurring  of 


148  SYSTEMATIC    FUNCTIONS 

the  territories  of  this  region  which  has  been  more  convulsed  during 
development. 

Yet  the  plexuses  are,  in  a  sense,  as  if  they  did  not  exist.  The  nerve 
trunks  which  arise  from  them  (radial,  median,  ulnar,  crural,  sciatic, 
etc.)  form  an  artificial  group  of  root  fibres,  in  which  no  very  definite 
functional  arrangement  can  be  detected.  A  knowledge  of  the  areas 
subjected  to  these  groupings  is  useful  when  their  respective  trunks 
are  individually  involved  by  paralysis  ;  or,  again,  if  it  is  desired  to 
investigate  them  experimentally.  But  the  arrangement  of  these  fibres, 
as  regards  their  course,  that  is  to  say,  far  from  their  origin  and  their 
termination,  does  not  correspond  to  any  real  systematization  ;  on 
the  other  hand,  the  relations  of  the  roots  with  their  dermatomeres 
is  extremely  simple,  the  form  of  the  dermatomere  being  generally 
obvious,  and  their  succession  in  the  order  of  that  of  the  roots  them- 
selves. 

Mutual  interpenetration  of  the  territories. — Such  is  the  very  simple 
scheme  of  the  cutaneous  territories  as  regards  their  correspondence 
with  the  spinal  roots.  Yet  these  territories  must  not  be  regarded  as 
having  determinate  boundaries.  Every  one  of  them  is  invaded,  at  its 
confines,  by  the  sensory  nerves  of  neighbouring  territories  (superior 
and  inferior),  which  are  superposed  on  its  own  territory,  some  in  one 
half,  others  in  the  other  half  of  its  surface.  It  is  obvious  that  these 
areas  of  overlapping  increase  the  size  of  the  area  of  distribution  of 
each  root,  but  they  do  not  alter  the  general  form  of  this  area,  as  it  is 
easy  to  understand.  It  merely  follows  that  isolated  section  of  a 
posterior  root  will  in  no  case  lead  to  the  precise  and  definite 
an£esthesia  of  a  dermatomeric  cutaneous  band  ;  to  express  the  matter 
more  clearly,  experiment  having  shown  that  it  is  as  described,  it  has 
hence  been  concluded  that  overlapping  zones  must  exist.  Thus  the 
isolated  section  of  a  single  posterior  root  will  not  point  out  to  us  its 
area  of  cutaneous  distribution. 

Warned  by  this  experimental  fact,  Sherrington  has  overcome  the 
difficulty  by  allowing  a  single  root  to  remain  intact,  amongst  several 
others  which  have  been  cut,  either  in  front  or  behind  it  (in  animals). 
In  this  way  a  sensitive  zone  is  defined  (that  of  the  root  which  has 
been  spared)  between  two  anaesthetic  surfaces. 

In  man,  who  is  able  to  give  an  account  of  his  sensations,  as  the 
result  of  multiple  or  isolated  lesions  of  the  roots  (confirmed  by 
autopsy),  there  may  be  observed,  not  merely  total  paralysis,  but 
diminution  of  sensibihty,  which  is  the  consequence  of  it,  and  in  this 
way  it  may  be  possible  to  deduce  the  topography  of  individual 
radicular  innervations  (Thornburn,  Allen  Star,  Head). 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    149 

The  results  thus  supphed  clinically  agree  fairly  well  with  those 
furnished  by  physiological  experiment. 

3.  Radicular  muscular  territories. — Isolated  stimulation  of  a  motor 
root  causes  the  contraction  of  several  muscles,  sometimes  of  a  fairly 
large  number,  according  to  its  size  and  the  number  of  its  component 
elements.  Hence  it  has  its  own  special  territory  of  motor  action,  just 
as  the  corresponding  posterior  root  has  its  sensory  territory  on  the 
surface  of  the  skin.     The  first  is  far  from  having  the  regularity  of  the 


illiiiuiuiuirii\lil\\li\ 


Fig.   59. — Distribution  of  the  sensory  fibres  of  the  thoracic  nerves  (diagram)   (after 

•  Sherrington).  j  ;., 

The  areas  of  the  III^'  and  the  V  dorsal  join  each  other  by  each  overlapping  half  of  the  inter- 
mediary ten-itory  of  the  IV*". 


second.  On  the  other  hand,  each  muscle  individually  generally  receives 
tnotor  elements  from  several  neighbouring  anterior  roots  ;  thus  it  follows 
that  the  territories  of  motor  muscular  innervation  interpenetrate  (Hke 
the  sensory  zones  of  the  skin),  and  this  interpenetration  has  no  longer 
in  the  myomeres,  the  regularity  which  distinguishes  it  in  the  derma- 
tomeres. 

From  the  practical  point  of  view  (diagnosis  of  motor  paralysis, 
surgical  intervention  in  nerves),  a  series  of  tables  maybe  constructed, 
displaying,  by  a  given  number,  the  muscular  area  to  which  each 
anterior  root  is  distributed,  and  the  cutaneous  territory  presided  over 
by  each  posterior  root.  So  far,  treatises  on  anatomy  have  preferably 
prepared  tables  which  point  out  the  field  of  muscular  and  cutaneous 
distribution  of  the  nerve  trunks  (radial,  ulnar,  median,  crural,  sciatic, 
etc.),  arising  from  the  plexuses,  that  is  to  say,  after  the  intermixture 
of  the  roots  in  these  plexuses,  and  which  are  of  use  in  the  case  of 
lesion  of  the  trunks,  or  of    surgical  intervention  in  connexion  with 


150  SYSTEMATIC    FUNCTIONS 

them.  A  knowledge  of  the  second  in  no  sense  dispenses  with  that 
of  the  first  ;  because,  as  is  thus  seen,  they  are  not  superposed  in 
any  way. 

A  radicular  trunk  is  not  a  functional  unity. — Have  the  roots  which 
numerically  follow  one  another  at  the  origin  of  a  nervous  whole,  such 
as  the  brachial  plexus,  individual  special  functions,  such  as  extension, 
flexion,  adduction,  abduction,  for  the  motor  roots  of  the  superior  ex- 
tremity ?  Ferrier  and  Yeo,  P.  Bert  and  Marcacci,  who  were  the  first  to 
study  this  question  experimentally,  have  answered  in  the  affirmative. 
But  their  results  have  been  contradicted  by  Lannegrace  and  Forgue,  who 
have  not  been  able  to  find  between  each  motor  root  and  its  muscular 
territory  anything  beyond  a  purely  anatomical  or  topographical  cor- 
respondence, without  any  suggestion  of  function.  The  component 
elements  of  the  same  root  resemble  one  another,  in  that  they  all 
possess  a  motor  function  ;  but  these  elements  enter  into  the  com- 
plexus,  which  makes  use  of  their  function  in  a  variety  of  ways.  The 
natural  movements,  even  the  simplest,  imply,  indeed,  an  action  which 
is  at  the  same  time  gradated  and  successive  of  the  muscles  which 
execute  them  ;  in  other  words,  in  order  to  effect  the  movements,  a 
co-ordination  both  as  regards  time  and  space  of  the  contraction  of 
these  muscles  is  necessary  ;  this  is  the  result  of  associations,  carried 
out  in  the  grey  matter,  between  neurons  which  are  more  or  less 
approximated  or  separated,  and  hence  which  do  not  necessarily  belong 
to  the  same  group  of  original  cells  giving  origin  to  a  root. 

Dissociation  of  the  root  in  its  bundles. — In  fact,  the  total  artificial 
excitation  of  an  isolated  anterior  root  may  certainly  produce  a  defined 
movement  in  the  corresponding  limb  (flexion,  extension,  adduction, 
etc.),  but  this  is  simply  due  to  the  fact  that,  the  excitation  acting 
upon  a  collection  of  fibres  whose  functions  are  different  or  antago- 
nistic, the  resulting  effect  arises  as  regards  the  strongest  muscle,  or 
that  which  receives  the  strongest  stimulation. 

If,  as  Russell  has  done,  an  anterior  root  be  dissociated  into  its 
component  bundles,  and  each  one  of  these  be  separately  stimulated, 
different  and  sometimes  antagonistic  movements  will  be  aroused  by 
these  localized  excitations.  This  proves  that  the  same  root  is  dis- 
tributed to  several  muscles  whose  function,  further,  is  not  univocal.  Con- 
versely, the  same  inuscle  receives  the  fibres  of  several  roots.  Practically, 
these  results  explain  how  it  is  that  isolated  paralysis  of  an  anterior 
root  only  causes  transitory  disturbances  of  movement. 

These  facts  are  in  agreement  with  those  of  the  same  order  observed 
clinically  (Allen  Star,  Mills,  Kaiser). 

4.  Mixed  nerves. — The  anterior  and  the  posterior  roots  intermingle 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    151 

their  fibres  just  beyond  the  spinal  ganghon,  and  thus  form  a  mixed 
nerve. 

At  the  spot  where  the  mixed  trunk  of  the  nerve  pair  emerges  from 
the  inter-vertebral  foramen  it  receives  from  the  ganglia  of  the  great 
sympathetic  sensori-motor  elements  of  a  new  order,  which  still  further 
complicate  its  composition.  Thus  it  is  mixed,  not  only  by  the 
addition  of  sensory  and  motor  elements,  but  also  by  that  of  elements 
possessing  different  varieties  of  sensation  and  of  motion. 

Thus  constituted  and  completed,  the  mixed  trunks  to  which  the 
nerve  pairs  give  origin  extend  to  the  periphery,  where  they  are 
distributed  to  definite  territories  which  are  arranged  in  gradated 
order  corresponding  to  that  (or  nearly  so)  of  the  roots  from  which 
they  arise. 


Am.  roof. 


Sinu-vert.  V .  .  . / 


Symp.  Gangli. 


Int.  branch. 


Common  Br. 


-     La'.er  br. 


Fig.   60. — General  arrangement  of  a  spinal  nerve  (diagram). 
An  intercostal  nerve  is  taken  as  a  type. 


These  territories  are,  some,  cutaneous  {dermatomeres) ;  others  mus- 
cular {myomeres),  and  yet  others  visceral  (these  may  be  called 
{splanchnomeres) . 

Definitions  and  Distinctions. — These  divisions  are  not  so  absolute  as  would  at 
first  sight  appear.  The  skin  does  not  wholly  represent  the  tactile  sense,  of  which, 
it  is  true,  it  is  the  accredited  organ  ;  the  viscera  penetrate  it  to  a  marked  degree 
under  the  form  of  vessels,  glands  or  other  organs,  whose  function  is  iinconscious 


152  SYSTEMATIC    FUNCTIONS 

and  involuntary.  The  muscles  do  not  represent  solely  animal  movement  ;  the 
vessels  equally  penetrate  them  ;  and,  further,  a  kind  of  sensation  is  acqmred  by 
them  which  is  intermediate  between  that  of  the  skin  and  that  of  the  viscera.  As 
regards  the  viscera,  properly  so-called,  if  they  send  prolongations  to  the  skin 
and  the  muscles,  they  do  not  in  return  receive  anything  from  these  organs,  to 
which  tl;ey  serve  a?  a  fundamental  and  indispensable  base.  The  words  derma- 
tomere,  myomere,  splanchnomere,  will  thus  possess  different  senses,  according 
as  to  whether  the  essential  function,  or  the  totality  of  the  functions,  which  are 
represented  in  them  are  considered  ;  according  also  as  to  whether  the  essential 
part  of  an  organ,  or  the  prolongations  which  it  furnishes  to  others,  is  taken  into 
account. 

The  constitution  of  the  metamere,  above  all,  that  of  its  nervous  system, 
explains  these  distinctions.  The  really  fundamental  portion  of  this  latter  consists 
of  the  ganglia  of  the  great  symjoathetic.  From  the  vertebral  ganglion  branches 
arise  which  proceed  to  the  viscera,  and  which,  following  the  vessels  wherever 
they  penetrate,  finally  attain  the  whole  field  of  the  metamere  ;  this  is  the  origin 
of  the  vegetative  system.  As  regards  the  intestine  (and  the  large  viscera),  these 
branches  continue  isolated.  As  regards  the  skin  and  the  muscles,  they  are  indeed 
duplicated  by  others,  which  skirt  them,  and  which  represent  conscious  sensibility 
and  voluntary  movement  :  this  is  the  oi'igin  of  the  animal  system.  Their  origins 
are  distinct  from  those  of  the  preceding,  and  are  in  the  spinal  ganglia  and  the 
grey  matter  of  the  spinal  cord.  They  accompany  the  sympathetic  branches  (as 
they  become  preponderant,  it  is  generally  said  that  they  are  accompanied  by 
them)  in  the  myomere  and  the  dermatomere.  They  form  with  regard  to  the 
others  a  supplemental  and  perfected,  differentiated  system.  They  assume  the 
function  of  external  life,  and  from  this  fact  have  notliing  in  common  with  the 
viscera,  which  are  organs  of  nutrition,  while  the  converse  is  not  so. 

When,  in  order  to  define  the  portions  of  the  nervous  system  which  (develop- 
ment being  finished)  have  retained  the  metameric  arrangement,  we  call  the  roots, 
medullary,  we  omit  an  important  portion  of  the  nervous  system  which  has  pre- 
served this  disposition  ;  these  are  the  branches  (direct  or  intermingled  with  the 
mixed  trunk)  which  arise  from  the  ganglia  of  the  sympathetic  chain,  and  which 
have  the  same  distribution  as  the  corresponding  roots.  On  the  other  hand, 
when,  in  order  to  furnish  an  example  of  true  metamerism,  we  bring  forward 
these  same  roots,  the  designation  is  only  correct  so  far  as  we  restrict  it  to  the 
conscious  voluntary  elements  of  these  roots  ;  these  alone  obey  the  usual  laws 
of  metamerism,  while  the  unconscious  or  vegtative  elements  elude  them.  These 
latter  indeed  have  not,  like  the  first,  a  direct  com-se  from  the  segment  of  the  cord 
to  the  peripheral  nerve  for  which  they  are  destined  by  the  corresponding  roots  ; 
but,  arising  either  above  or  below  the  ganglion  which  collects  them,  they  pass 
for  a  certain  distance  vertically  into  the  chain  of  the  great  sympathetic.  The 
chain  of  the  sympathetic  destroys  the  metamerism  of  the  vegetative  system,  just  as 
the  organization  of  tlie  spinal  cord  destroys  tJiat  of  the  animal  system. 

Trophic  disturbances. — Among  the  facts  which  indicate  metamerism  of  the 
nervous  system,  trophic  disturbances  of  the  skin  have  often  been  emphasized. 
Trophic  troubles  are  motor  phenomena  of  a  special  order.  It  is  proved,  both 
experimentally  and  clinically,  that,  in  many  cases,  their  appearance  depends  on 
the  nervous  system.  The  existence  of  nerves  whose  function  is  solely  and  speci- 
fically trophic  is  no  longer  admitted,  but  trophicity  is  regarded  as  a  function  of 
the  nervous  system.  The  disorders  of  nutrition  may  sometimes  affect  the  same 
distribution  as  the  areas  of  anaesthesia  ;.  some  are  accompanied  with  pain,  as  for 
instance,  herpes  zoster.  These  peculiarities  have  led  to  them  being  regarded  as 
arising  from  an  alteration  of  the  sensory  trunks,  especially  the  ganglia  of  the 
posterior  roots  (Baerensprung).     It  has  been  thought  that  from  this  alteration 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    153 

of  the  sensory  nerves  it  would  be  justifiable  to  infer  the  origin  of  the  nervous 
action ;  in  this  case  the  action  would  be  strongly  reflsx  ;  and  would  be  reflected 
on  the  skin  (Brissaud). 

Centrifugal  cutaneous  nerves. — But  the  posterior  roots  contain  centrifugal 
fibres  ;  and  it  is  i^ossible  that  certain  of  these  fibres  proceed  to  the  fixed  elements 
of  the  skin,  just  as  there  are  those  which  go  to  the  glandular  cells  of  this  structure. 
The  alteration  of  these  fibres  and  the  perversion  of  function  in  the  cutaneous 
covering,  which  is  the  result  thereof,  leads,  in  the  end,  to  a  modification  of  its 
structvu-e  (trophic  disturbance).  The  areas  of  these  neuro-trophic  dermatoses 
may  then  be  superposed  on  those  of  the  anaesthetic  zones,  if,  as  is  probable,  the 
centrifugal  fibres  of  the  posterior  root  have,  more  or  less  accvirately,  the  distribu- 
tion of  the  centripetal  fibres  of  the  same  root. 

Segmentary  alterations  of  sensation  and  of  nutrition. — Trophic  disturbances 
and  jDartial  anesthesia  affect  an  equally  regular  form  in  certain  cases,  but  have 
an  orientation  altogether  different  to  that  of  the  preceding.  Instead  of  being 
zonal,  the  cutaneous  lesions  are  segmentary.  This  arrangement  is  particularly 
striking  in  the  limbs  (dermatoses  assuming  the  form  of  a  glove,  that  of  a  sleeve. 


Hand 


Fig.   61. — Diagram  of  the  metameric  and  segmentary  distribution  of  the  nerves  of  the 

upper  limb  (after  Brissaud). 

The  cervical  enlargement  of  the  si^inal  cord  is  divided  bj-  horizontal  lines  into  three  metameres 
to  which  the  roots  Ri,  R2,  Rs^  going  to  the  thoracic  limb,  correspond  ;  by  vertical  lines  into 
three  segments  Mi,  M2,  il-,  of  whicli  the  deepest  gives  off  nerves  of  the  arm,  the  middle  one 
nerves  of  the  forearm,  and  the  most  superficial  nerves  of  the  hand. 


etc.).  In  order  that  such  forms  may  be  the  result  of  limited  lesions  of  the  grey 
substance  of  the  spinal  cord,  they  must  be  inscribed  there  in  the  arrangement 
of  the  origins  of  the  nerves.  According  to  Brissaud,  the  spinal  cord  is  not  only 
formed  of  superposed  neurotomes  (corresponding  primitively  to  the  roots  super- 
posed in  the  same  order),  but  its  grey  matter  presents,  in  its  lateral  thickness, 
superadded  layers,  which  reinforce  it  at  the  site  of  equally  superadded  portions 


154  SYSTEMATIC    FUNCTIONS 

(which  are  the  superior  and  inferior  extremities)  by  giving  origin  to  its  enlarge- 
ments (cervical  and  lumbar).  In  these  enlargements  the  most  superficial  layers 
are  those  which  sujoply  the  nerves  of  the  hand  or  foot ;  the  deepest,  those  which 
furnish  the  nerves  of  the  shoulder  and  of  the  hip.  Hence  it  is  easy  to  iinderstand 
how  isolated  alterations  of  these  nerves  may  give  rise  to  lesions  of  a  form  also 
singular  in  its  regularity.  Anaesthesia  also  is  subservient  to  the  same  disposi- 
tion. 

Sensory  visceral  areas. — When  the  large  viscera  are  the  seat  of  a  lesion  (especi- 
ally inflammatory),  their  ordinarily  unconscious  sensibility  becomes  conscious, 
and  we  perceive  the  pathological  excitation  of  their  sensory  nerves  under  the 
form  of  pain.  But  this  excitation,  on  arriving  at  a  medullary  segment,  is  (in 
consequence  of  its  abnormality  and  of  the  error  to  which  it  gives  rise)  often  ex- 
teriorized in  the  cutaneous  nerves  which  terminate  in  this  segment.  Head  has 
made  use  of  this  circumstance  in  order  to  ascertain  the  medullary  segments  which 
correspond  to  each  of  the  large  viscera  and  to  each  of  their  principal  portions. 

Clinical  phenomena  of  this  kind  have  been  long  known,  for  example,  pairh 
in  the  left  arm  and  the  left  little  finger  in  angina  pectoris  ;  pain  in  the  right 
shoulder  in  hepatic  colic,  that  in  the  testicle  in  renal  colic.  Mackenzie  has  also 
observed  that,  in  intestinal  obstruction,  cutaneous  pain  is  situated  above  the 
umbilicus,  when  the  obstacle  is  situated  in  the  small  intestine,  and,  on  the 
contrary,  between  this  point  and  the  symphysis  pubis  when  the  obstruction  is 
in  a  portion  of  the  large  intestine. 

In  order  to  determine  the  visceral  sensoiy  areas.  Head  takes  into  account  not 
merely  these  painful  radiations,  but  also  the  hypercesthesia  which  is  obvious  in 
certain  cutaneous  zones  under  the  influence  of  slight  stimulation  (pressure).  He 
has  proved  the  existence  of  a  large  number  of  hyperagsthetic  zones,  which  are 
very  diversely  situated,  and  whose  relation  to  the  roots  of  nerves,  and  hence,  to 
the  corresponding  medullary  segments,  he  has  endeavoured  to  ascertain. 

The  reasoning  on  which  these  researches  are  based  is  the  following  :  these 
hypersesthetic  zones  (according  to  Head)  can  be  superposed  on  the  anaesthetic 
zones  which  are  observed  in  the  lesion  of  the  roots  and  of  the  corresponding 
medullary  segments,  and  whose  areas  have  been  determined  by  physiological 
and  anatomical  clinical  methods.  The  hyperaesthetic  zone  indicates  the  affected 
root.  Clinical  experience,  on  the  other  hand,  showing  that  such  and  such  a  zone 
is  hyperaesthetic  when  such  and  such  a  viscus  is  diseased,  we  are  hence  justified 
in  concluding  that  the  sensory  nerves  of  this  viscus  and  of  the  hyperaesthetic 
zone  (although  topographically  they  may  be  far  removed)  terminate  in  the  spinal 
cord  in  common  nuclei.  It  is  these  common  nuclei  which,  receiving  the  patho- 
logically exaggerated  irritations  of  the  inflamed  viscus,  exteriorize  them  in  the 
skin.  This  external  manifestation  may  thus  become  a  diagnostic  aid  as  regards 
the  affected  viscus. 

Such  is  the  principle  of  this  method.  Practically  it  still  presents  too  much 
uncertainty,  and  the  results  have  proved  too  discordant  for  us  to  be  able  to  give 
here  a  detailed  table,  this  table  still  requiring  very  important  revision.  It  may 
be  added  that  the  proofs  are  too  indirect  in  nature,  and  lend  themselves  to  too 
many  objections,  to  be  accepted  without  discussion. 

The  relations  pointed  out  between  the  hyperaesthetic  zones  of  Head  and  vis- 
ceral lesions  may,  however,  retain  their  symptomatological  value,  while  still 
leaving  untouched  the  problem  of  the  systematization  of  the  sensory  visceral 
nerves. 

C.     CRANIAL  NERVES— FUNCTIONAL  DETERMINATIONS 
1.  Morphological  regularity  of  the  spinal  cord. — In  the  spinal  cord, 
the  origins  of  the  sensory  and  motor  nerves  are  systematically  arranged 


SENSATION  AND  MOTION— THEIR  RELATIONSHIP      155 


in  a  simple  and  regular  manner,  so  that  they  can  be  recognized  at  first 
glance,  it  being  assumed  that  experiment  has  determined  their  func- 
tions. Every  nerve  pair  has  its  component  elements  arranged  in  the 
same  manner,  and  experiments  carried  out  on  one  are  applicable  to  all. 

2.  Irregularity  of  the  medulla  oblongata. — In  the  medulla  oblongata 
this  systematic  arrangement  has  disappeared,  or  has  become  almost 
unrecognizable  ;  it  is  on  this  account  that  there  is  a  question  con- 
cerning the  cranial  nerves.  The  sensory  and  motor  elements  form  in 
it,  indeed,  irregular  groups  which  destroy  the  systematic  arrangement 
by  which  they  can  be  so  easily  recognized  elsewhere,  by  merely 
regarding  their  relative  position  ;  hence  it  is  necessary  to  investigate 
these  elements  of  diverse  function  by  experimenting  directly  on  each 
of  the  nerve  trunks  which  arise  from  the  medulla  oblongata. 

New  superadded  formations. — The  medulla  oblongata  is  a  place  of 
transition  ;  the  symmetrical  and  regular  medullary  cylinder  ends  in 
it  ;  the  cerebral  ex- 
pansion commences  in 
it,  or  is  more  or  less 
prepared  in  it  by  acces- 
sory formations. 
These  new  masses,  of 
different  function  and 
type,  at  fu-st  sight  upset 
the  primitive  scheme  of 
the  medullar}"  edifice. 
Nevertheless,  modified 
traces  of  it  may  be  re- 
cognized, but  for  this 
it  is  not  too  much  to 
unite  the  data  furnished 
by  experiment  \vith 
those  of  morphology. 

Vertebral  Theory  op 
THE  Cranium. — The  classi- 
fication of  the  cranial 
nerves  is  connected  with 
the  old  theory  of  Goethe 
and  Oken,  a  theory  often 
fiirbished  up,  and  which 
we  will  attempt  to  describe 
in  a  few  words. 

So  far  as  concerns  the  cranial  nerves,  tliere  is  a  double  problem  :  ( 1 )  to  recog- 
nize the  equivalents  of  the  anterior  and  posterior  roots  ;  (2)  the  nerve  pairs 
being  constituted,  to  ascertain  their  metamerism. 


Mei.  Spinal. 


Fig.   62. — Topography  of  the  nuclei  of  the  cranial 
nerves  situated  in  the  floor  of  the  4th  ventricle. 
The  motor  nuclei  in  red  the  sensory  nuclei  in  Ijlue. 


156 


SYSTEMATIC    FUNCTIONS 


Ventral  and  dorsal  nerves. — In  the  spinal  cord  each  pair  is  formed  by  a  ventral 
nerve  (the  anterior  root)  and  a  dorsal  nerve  (the  posterior  root).  The  ventral 
nerve  is  exclusively  connected  with  the  muscles  ;  or,  in  other  words,  it  is 
functionally  motor.  The  dorsal  nerve  is  connected  with  the  skin  ;  in  other 
words,  it  is  sensory.  It  must  be  added  that  in  the  dorsal  nerve  some  centrifugal 
elements  exist,  but  in  limited  number,  which  thus  make  it  (however  small 
their  number  and  their  importance)  a  mixed  nerve. 

The  ventral  nerves  (motor  nerves)  arise  from  the  cells  of  the  anterior  cornua, 
emerge  from  the  ventral  path  of  the  nerve  axis,  and  are  distributed  to  the  muscles 
taking  origin  in  the  myotomes. 

The  dorsal  nerves  (sensory  nerves)  arise  from  the  cells  of  the  spinal  ganglia, 
penetrate  the  spinal  cord  by  the  dorsal  portion  of  the  nerve  axis,  and  are  func- 
tionally related  to  the  organs  of  touch  situated  in  the  skin.     Their  motor  fibres 


.  Spinal  access. 


Hypogl. 


Fig.  63. — Apparent  origin  of  the  cranial  nerves  at  the  base  of  the  brain  (after  Hirschfeld). 


are  very  few  and  have  only  been  studied  so  far  as  regards  their  function  in  those 
varieties  which  make  their  classification  difficult  (vaso-motor  elements). 

In  the  cranium,  the  series  of  ventral  nerves  would  be  represented  by  the  motor 
nerves  of  the  eye  (oculo-motor,  external  oculo-motor  or  sixth  nerve,  pathetic 
or  fourth  nerve)  and  the  hypoglossal.  But  the  fourth  nerve  is  still  under  dis- 
cussion on  account  of  its  posterior  exit  ;  the  series  of  dorsal  nerves  would  be 
represented  by  the  trigeminal,  the  facial,  the  glosso-pharyngeal,  the  pneumogastric 
and  the  spinal  accessory. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    157 

The  nerves  of  special  sense  are  generally  left  unclassified,  on  account  of  their 
extremely  pronounced  differentiation. 

Comparative  morphology. — In  the  case  of  man,  the  arrangement,  dorsal  and 
ventral,  of  these  two  series  is  not  very  obvious,  but  it  is  much  more  so  in  that  of 
the  inferior  vertebrata.  In  any  case  the  ventral  series  represents  those  nerves 
which  are,  in  the  cranium,  the  continuation  of  those  which  arise  from  the  antero- 
external  group  of  the  anterior  horn  of  the  spinal  cord,  and  which  are  distributed 
to  the  muscles  originating  in  the  myotomes.  Difficulties  and  objections  arise, 
on  the  other  hand,  when  the  dorsal  cranial  nerves  are  compared  with  the  posterior 
spinal  roots.  The  motor  elements  which  enter  the  trigeminal,  facial,  pneumo- 
gastric  and  spinal  accessory,  are  of  such  great  importance  that  they  can  scarcely 
be  compared  to  the  few  centrifugal  fibres  of  the  posterior  roots.  Fiirther, 
while  the  latter  have  a  connexion  only  with  the  skin,  the  sensory  cranial  nerves 
are  distributed  to  the  digestive  mucous  membrane. 

Superadded  nervous  apparatus,  branchial  nerves. — This  difference  is  explained, 
according  to  Kupj^fer,  by  the  existence,  in  the  region  of  the  dorsal  cranial  nerves, 
of  a  superadded  system,  the  system  of  branchial  nerves,  which  is  wanting  in  the 
spinal  nerves.  This  branchial  nerve  distributes  its  motor  ramifications,  not  to 
the  muscles  derived  from  the  dorsal  segmented  portion  of  the  mesoderm  (somites, 
myomeres,  myotomes),  which,  in  the  craniun:i,  as  in  the  head,  are  innervated  bj' 
the  ventral  nerves  (eye  and  tongue  muscles  ;  oculo-motor  and  hypoglossal  nerves), 
but  to  other  muscles,  which  are  wanting  in  the  trunk  and  are  present  in  the  head, 
and  which  originate  from  the  lateral  mesodermic  nerve,  segmented  by  the 
branchial  clefts. 


Buccal  foss. 
Olfact.  foss. 


Myotome 


Branchial  arches 
{lateral  plates) 

Branchial  cleft 


Fig.   fi4. — Diagrammatic  representation  of  the  cephalic  extremity  of  an  inferior  verte- 
brate (after  the  description  of  Van  Wijhe). 
The  cejahalic  mesoderm  (myotomes  and  lateral  plates)  in  red. 

The  dorsal  nerves,  in  the  cranial  region,  are  thus  the  result  of  the  union  of  a 
postei'ior  root  with  a  branchial  nerve. 

Metamerism. — In  the  trunk,  primitive  metamerisation  of  the  individual  is 
rendered  evident,  in  the  adult,  by  the  vertebral  bodies  and  the  corresponding 
nerve  pairs  which  emerge  in  the  interval  between  them.  In  the  other  organs, 
including  the  nerve  axis  and  the  whole  of  the  muscles,  there  is  no  trace  of  this 
arrangement.  In  the  cranivim,  the  skeleton,  as  also  the  muscles,  are  a  very 
untrustworthy  and  arbitrary  evidence  if  examined  in  the  adult.  It  is  necessary 
to  have  recourse  to  the  antecedent  arrangements  in  order  to  recognize  metameri- 
sation in  this  region,  and  Huxley,  and  after  him  Gegenbaiu",  find  the  evidence 
of  this  in  the  disposition  of  the  branchial  apparatus,  each  of  the  visceral  arches 
of  wliich  would  correspond  to  a  metamere  provided  with  its  nerve  pair. 

Myomeres  and  branchiomeres. — But,  with  Van  Wijhe,  it  is  necessary  to  take 
into  account  the  segmentation  of  the  cephalic  mesoderm,  which  gives  rise,  in  the 
skvill  as  in  the  trunk,  to  a  certain  nvunber  of  somites  or  myomeres ;  and  this  so 
nuich  the  more  as,  the  strict  and  exclusive  relationship  of  the  somites  with  the 


158  SYSTEMATIC    FUNCTIONS 

ventral  roots  being  allowed,  we  shall  thus  be  supplied  with  a  fixed  base  for  the 
numeration  of  the  metameres.  The  solution  of  the  question  would  be  clear  and 
definite  were  it  possible  to  be  certain  as  to  the  exact  number  of  the  segments. 
But  the  rapid  changes  which  ensue  in  the  couj-se  of  evolution  upset  at  every 
moment  the  actual  condition,  certain  of  the  myomeres  falling  into  a  state  of 
atrophy  very  soon  after  their  appearance.  Yet  further,  the  parallelism  between 
the  somites  and  the  visceral  arches  is  itself  of  short  duration  and  gives  rise  to 
micertainty,  the  myomerism  and  the  branchiomerism  not  proceeding  equally. 
It  thus  results  that  the  dorsal  and  ventral  nerves  can  only  be  classed  separately, 
without  endeavouring  to  collect  them  together  into  exactly  corresponding  pairs ; 
and  hence  the  determination  of  the  ventral  nerves  is  difficult  from  the  metameric 
point  of  view. 

(a)  Physiological  characters  of  the  nerve  pair. — Physiology, 
which  is  based,  above  all,  on  the  study  of  function,  allots  to  the 
constitution  of  the  nerve  pair  other  characters  chiefly  drawn  from 
experiment.  The  nerve  pair  is  in  this  respect  essentially  made  up  of 
elements  which  are  functionally  associated  in  the  constitution  of  a  simple 
reflex  axis,  as  they  are  in  the  metamere.  CI.  Bernard  emphasized 
another  character,  which  expresses  the  signification  of  the  preceding 
one  :  Tico  nerves,  one  sensory  and  the  other  motor,  form  a  ^physiological 
pair,  tvhen  the  first  gives  to  the  second  its  recurrent  sensibility.  When 
it  is  remembered  that,  as  CI.  Bernard  holds,  the  terminal  apparatus 
of  this  recurrent  sensibility  is  situated  at  the  surface  of  the  spinal 
cord  and  of  its  membranes  regarded  as  receptive  of  excitation,  in  the 
very  region  of  the  roots  under  consideration,  the  functional  associa- 
tion of  the  two  nerves  will  be  seen  to  be  strengthened. 

Contingence  of  the  associations  in  the  course  of  functional 
activity. — But  the  physiologist  also  knows  that  these  connexions  are 
changeable,  according  to  the  progress  and  the  necessities  of  the  func- 
tions, and  he  is  therefore  the  less  surprised  on  learning  of  the  diffi- 
culties which  prevent  a  rigid  classification  of  these  associations.  For 
him  the  conception  of  the  nerve  pair  has  a  symbolical  value,  or  one 
for  convenience  of  description.  Having  made  these  reserves,  it  may 
be  useful  to  point  out  those  amongst  the  cranial  nerves  which 
approach  the  most  closely  to  the  primitive  and  ideal  scheme  which 
has  been  studied  with  regard  to  the  spinal  roots. 

Thus  we  find,  in  the  trifacial  or  trigeminal  those  characters  which 
are  most  clearly  characteristic  of  a  sensori-motor  nerve  pair,  but  of 
a  nerve  pair  which  has  already  lost  its  regularity  and  its  symmetry, 
and  which  must  be  completed  or  dissociated  if  it  is  desired  to  re- 
estabhsh  in  it  equilibrium  between  the  sensory  and  motor  elements. 

Nerve  pair  approximating  the  spinal  type. — The  trigeminal  nerve 
takes  origin  in  the  medulla  oblongata  through  the  pons  by  two  roots, 
the   one   sensory,   bearing  a  ganglion   {Gasserian  ganglion),   which  is 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    159 

obviously  the  equivalent  of  the  ganglion  of  a  posterior  spinal  root ; 
the  other  motor,  which  proceeds  to  form  with  the  preceding  a  mixed 
nerve  by  interminghng  of  its  fibres.  This  is  not  merely  an  induction 
from  the  resemblance  of  form  ;  if  an  experiment  is  made  (with  more 
difificulty,  it  is  true)  on  the  roots  of  the  trigeminal  similar  to  that 
on  those  of  the  spinal  nerves,  sensory  and  motor  paralysis  may  be 
induced  by  the  section  of  the  nerve  ;  by  the  stimulation  of  each  of 
the  two  roots  sensation  and  motion  may  be  elicited. 

But  this  nerve  (as  its  name  points  out)  has  three  branches,  cor- 
responding to  the  three  large  subdivisions  of  the  face,  and  of  these 
three  branches  the  third  only  (inferior  maxillary  nerve)  receives  the 
elements  of  the  motor  root.     Hence  the  trifacial  pair  must  be  com- 


Op'it.  n 


escend.  Motor  R. 


;  -  Princ.  Mnior  N. 


Desc.  Spiiuil  R. 


Sup.  Max.  X.         Inferior  Max.  y. 

Fig.   65. — Diagram  of  the  real  origins  and  the  constitution  of  the  trigeminal   (after 

Van  Gehuchten). 

pleted  by  the  addition  of  motor  elements.  These  elements  are  found 
in  the  purely  motor  trunks,  which  are  distributed  to  the  muscles  of 
the  orbit  and  which  supplement  the  first  branch  of  the  trigeminal 
(ophthalmic  branches),  which  confer  sensation  on  the  ocular  region  ; 
these  are  the  oculo-rnotor  nerve,  the  external  oculo-motor  nerve,  and  the 
pathetic. 

Functional  association  of  the  radicular  elements. — The  trifacial 
pair  is  obviously  sensori-motor.  It  corresponds  to  the  same  sense  as 
the  posterior  roots,  namely,  to  the  tactile  sense  or  that  of  general  sensa- 
tion. The  other  cranial  pairs,  more  or  less  strictly  so-called,  which 
take  origin  from  the  medulla  oblongata,  have  as  a  basis  either  purely 
sensory  nerves,  as  the  olfactory,  the  acoustic,  or  the  optic  ;    or  nerves 


160 


SYSTEMATIC  FUNCTIONS 


in  which  sensorial  elements  are  mixed  with  sensory  elements,  as  the 
glosso-pharyngeal  ;  or,  finally,  trunks  in  which  general  sensation  is 
mixed  up  with  obtuse  and  subconscious  sensation,  as  the  pneumo- 
gastric  and  spinal  accessory. 

Their  complexity. — These  associations  between  sensory  nerves  or 
those  of  special  sense,  and  motor  nerves,  are  from  the  point  of  view 
of  function,  both  multiple  and  variable.  Hence  they  are  in  no  sense 
exclusive  the  one  of  the  other.     The  motor  nerves  of  the  eye,  which 


Trij.  (G.  Gasser). 


Wrisberg. 
Acoustic  {Scarpa). 
61.  Ph.  (Andersh). 
Pneumo.  gust  [G.  PIe.c) 


L^<- 


Mot.  tri;.  (Mast.) 


Cervic  N. 


Fig. 


00. — Ganglia     of     origin 
sensory  cranial  nerves. 


of     the       Fig. 


Their  roots,  and  the  ascending  and  descend- 
ing branches  of  these  roots. 


GOa. — Nuclei  of  origin  of  the  cranial 
motor  nerves  (diagram). 

The  nuclei   are  seen  laterally  through  the 
cerebral  trunk  supposed  to  be  transparent. 


are  connected,  by  the  ophthalmic  branch  of  the  trigeminal,  Avith 
general  sensation,  are  equally  so,  by  the  optic  nerve,  with  the  sense 
of  vision,  and  may  be  connected  with  that  of  hearing,  or  of  any  other 
by  the  special  conducting  tracts  of  these  senses.  And  it  must  not  be 
forgotten  that  it  is  the  same  in  the  spinal  cord  ;  the  functional  bond 
of  union  Avhich  subsists  between  the  posterior  and  the  anterior  root, 
and  which  is  manifested  by  a  reflex  act,  is  interesting,  because  it 
illustrates  the  rough  sketch  of  the  nervous  system  ;  but  it  is  not 
strictly  necessary,  and  the  muscles  of  the  limbs  or  of  the  trunk,  as 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    161 

well  as  those  of  the  face,  are  functionally  associated  at  every  moment 
with  the  superior  senses. 

Another  example. — The  jacial,  with  its  two  roots,  of  wliich  one  (small  root) 
l^ears  a  small  ganglion  {geniculate  ganglion),  is  also  often  compared  to  a  spinal 
nerve  pair. 

Tlie  large  root  is  obviously  motor  ;  the  small,  known  as  the  nerve  of  Wrisberg, 
is  regarded  as  a  nerve  of  special  sense  ;  it  shares  with  the  glosso-pharjmgeal  the 
faculty  of  conferring  the  sense  of  taste  ;  by  the  chorda-tympani  it  proceeds  to 
the  tip  of  the  tongue,  while  the  glosso-pharyngeal  is  distributed  to  the  root  of 
the  tongue  ;  the  tip  and  the  root  of  the  tongue  comprise  the  area  of  the  sens© 
of  taste. 


Facia!  A'. 


Intern.  A', 


SolU.  F. 


aetnc.  Gangl 


Fig.   G7. — Facial  ner\e  and  intermediary  nerve  of  Wrisberg.     Facial  pair. 


Multiple  associations  of  the  original  elements. — The  motor  portion  of  the  facial 
nerve  does  not  go  to  the  muscles  of  the  tongue,  but  to  the  cutaneous  muscles  of 
the  face,  and  it  is  consequently  not  cormected  with  the  sense  of  taste  except  in  a 
wholly  contingent  manner.  The  motor  portion  of  the  facial  is,  on  the  contrary, 
connected  in  a  more  direct  manner,  although  a  still  very  partial  one,  with  the 
sense  of  hearing  by  the  branches  which  it  supplies  to  certain  muscles  of  the  ear 
(muscles  of  the  external  ear,  muscle  of  the  stapes).  The  acoustic  nerve  is  closely 
attached,  at  its  origins,  to  the  two  roots  of  the  facial,  and  passes  through  the 
same  orifice  as  the  latter  (internal  auditory  meatus)  before  separating  from  it  m 
order  to  proceed  to  the  internal  ear.  From  the  functional  point  of  view,  the 
facial  is  also  associated  with  the  sense  of  smell,  in  order  to  ensure  the  movements 
of  the  nostrils  connected  with  the  exercise  of  this  sense  ;  with  the  sense  of  sight, 
in  order  to  perform  the  movement  of  the  upper  lid  ;  and  very  generally  with 
the  tactile,  or  general  sensibility,  of  the  trigeminal. 

The  hypoglossal  nerve,  its  small  inconstant  root. — The  motor  nerve  of  the 
tongue,  whose  mvicous  membrane  is  supplied  with  the  organs  of  taste,  is  the 
hypoglossal.     Usually  it  is  formed  of  a  single  order  of  roots  (motor  roots)  ;   but 

P.  M 


162  SYSTEMATIC  FUNCTIONS 

sometimes  it  is  svipplied  with  a  small  root  bearing  a  ganglion,  and  thus  repro- 
duces the  tj'pe  of  the  spinal  nerve  pairs. 

Glosso-pharyngeal  ;  pneumo-spinal. — The  glosso -pharyngeal,  the  pneiuno- 
spinal  (formed  by  the  union  of  the  origins  of  the  pneumogastric  and  of  the  spinal 
accessory)  originally  contained  motor  and  sensory  elements  of  different  nature, 
which  have  caused  them  to  be  assimilated  to  the  fxinctional  pairs.  Their  centri- 
fugal and  centripetal  elements  are  mixed  from  their  exit  from  the  medulla  ob- 
longata ;  the  ganglia  which  they  pass  through  (ganglion  of  Elii-emitter  and 
ganglion  of  Andersch  in  the  first  ;  jugular  ganglion  and  plexiform  ganglion  in 
the  second)  are  partially  comparable  to  the  spinal  ganglia  of  the  i30sterior  roots. 
Overlapping  and  reciprocal  penetration  of  areas. — In  short,  all  the  motor, 
sensory,  nerve  trunks  and  those  of  special  sense  to  which  we  have  just  referred 
are  distributed  to  areas  wliich  overlap  each  other,  fit  together,  penetrate  each 
other,  and  are  more  or  less  superposed  ;  to  such  a  degree,  indeed,  that  only  by 
experiment  is  it  possible  to  determine  their  limits  and  to  unravel  the  complicated 
skein  formed  by  every  kind  of  fibre  which  is  woven  in  the  tissues  of  the  face  and 
of  the  neck  throvigh  their  multiple  anastomoses. 

As  they  present  themseh^es  to  our  observation  and  to  experiment  in  the  adult 
animal,  the  cranial  nerves  are.  some  of  them,  isolated,  such  as  the  olfactory  and 
the  acoustic  ;  while  others  reproduce,  more  or  less  definitely,  the  arrangement 
of  the  sj^inal  nerves  (trigeminal,  facial)  ;  others,  again,  have  their  sensori-motor 
elements  mixed  from  their  emergence. 

Method  of  study  and  description. — The  method  of  study  of  these  anatomical 
groujDings  is  based  on  a  double  analysis  ;  ( 1 )  it  is  necessary  to  separate  in  them 
the  sensory  from  the  motor  elements  ;  (2)  further,  to  separate  in  these  groups, 
the  different  sensory  and  motor  elements.  From  this  second  j^oint  of  view  the 
elements  are  divided  into  two  new  general  categories,  that  of  the  conscious  and 
that  of  the  unconscious,  as  will  be  explained  further  on.  Anatomically,  the 
imconscious  is  represented  by  the  great  sympathetic  and  its  bulbar  equivalents. 
On  account  of  the  intimate  intermixture  of  these  elements  with  the  majority  of 
these  nerves  whose  anatomical  arrangement  is  morjahologically  irregular,  it  is 
necessary,  in  order  to  obtain  perspicacity,  to  now  describe  the  cranial  sympa- 
thetic at  the  risk  of  repeating  this  description  when  we  commence  the  study  of 
the  unconscious  svstem  as  a  whole. 


(&)  Relations  with  the  Great  Sympathetic— In  the  spinal  cord 
each  nerve  pair  is  attached  to  a  ganghon  of  the  great  sympathetic  and 
is,  in  a  way,  completed  by  its  connexions  with  this  special  system. 
It  is  precisely  the  same  in  the  medulla  oblongata  ;  only  the  determi- 
nation of  the  elements  which  belong  to  it  presents,  in  this  region, 
greater  difficulties.  In  fact,  the  great  sympathetic,  in  its  strictly 
vertebral  portion,  follows  the  same  typical  and  regular  arrangement 
as  the  nerve  pairs  with  which  it  exchanges  communicating  branches. 
In  the  cranial  portion,  the  shocks  which  have  dissociated  the  primi- 
tive nerve  pairs  have,  at  the  same  time,  changed  the  morphological 
characters  by  which  they  are  recognizable,  and  compel  us  to  identify 
them  by  the  direct  authentication  of  their  functions. 

Normal  Type  of  these  Relations. — Yet,  the  normal  type  of  the  rela- 
tions of  the  great  sympathetic  with  the  other  nerves  has  not  entirely 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    163 

disappeared,  and  it  is  again  in  the  subordinate  divisions  of  tlie  tri- 
geminal that  we  recognize  it.  To  the  three  branches  of  distribution 
of  this  nerve  (ophthalmic  branch,  superior  maxillary  nerve,  interior 
maxillary  nerve)  are  attached  three  ganglia  {ophthalmic  ganglion, 
S'pheno-palatine  ganglion,  otic  ganglion)  ;  further,  a  fourth  ganglion 
{submaxillary  ganglion)  is  attached  to  a  large  branch  of  the  sub- 
maxillary nerve,  the  lingual  nerve,  all  of  these  ganglia  being  clearly 
those  of  the  great  sympathetic. 


Fig. 


(58. — Diagram  representing  the  principal  cranial  nerves  and  their  chief  anastomoses 
by  means  of  tlieir  ganglia,  in  the  dog. 


Ill,  oculo-motor  ;  V,  trigeminal  ;  VII,  facial  ;  IX,  glosso-pharyngeal  ;  X,  pneumogastric  ; 
XII,  hypoglossal. 

The  great  sympathetic  forms  •a^  common  trunk  (vago-sympathetic)  with  the  pneumogastric  in 
the  neck,  and  becomes  distinct  before  tlirowing  itself  into  the  superior  cervical  ganglion.  In 
the  skull,  the  sympathetic  cham  is  represented  by  a  branch  proceeding  from  the  superior  cervical 
gangUon  to  the  ganghon  of  Gasser,  and  from  thence  to  the  ophthalmic  spheno-palatine  and  otic 
gangha  of  the  trigeminal. 


The  trifacial  pair,  which  may  be  looked  upon  as  condensed,  when 
its  roots  and  its  Gasserien  ganglion  (the  equivalent  of  a  spinal  gang- 
lion) are  taken  into  consideration,  is,  on  the  contrary,  found  to  be 
dissociated,  when  its  sympathetic  ganglia  are  regarded. 

Cranial  sympathetic. — The  three  first  of  these  gangha  are  attached 
to  the  chain  of  the  great  sympathetic  by  a  double  branch,  which, 


164  SYSTEMATIC  FUNCTIONS 

leaving  the  superior  cervical  ganglion,  proceeds  to  join  them  ;  one 
of  these  branches  forms  the  carotid,  plexus  and  goes  to  seek  them 
separately  ;  the  other  (and  it  is  this  which  I  consider  to  form  the 
cranial  prolongation  of  the  cervical  cord)  terminates  in  the  Gasserien 
ganglion,  is  distributed  to  the  three  branches  of  the  trigeminal,  and 
by  the  intermediation  of  these  latter  comes  into  relationship  with  the 
three  gangHa  (ophthalmic,  spheno-palatine,  and  otic).  The  reality  of 
these  connexions  is  shown  by  experiment  :  excitations  applied  to  the 
cervical  cord  pass  through  these  ganglia  in  order  to  dilate  the  pupil, 
to  cause  certain  glands  to  secrete,  and  to  act  on  the  circulation  of 
certain  areas  of  the  face. 

Branches  of  distribution  and  branches  of  origin  of  the  sympathetic 
in  the  skull. — Like  the  spinal  pau's,  the  trigeminal  receives  elements 
from  the  great  sympathetic,  which  are  intermixed  with  its  branches 
of  distribution  and  proceed  to  the  apparatus  whose  function  it  pre- 
sides over  (vessels,  glands,  involuntary  muscles)  ;  but,  hke  the  spinal 
pairs,  it  supplies  in  its  turn  original  branches  to  the  ganglia  which 
correspond  to  it,  and  this  is  proved  by  experiment  :  the  stimulation 
of  the  origins  of  the  trigeminal  in  the  skull  has  the  same  effect  as 
that  of  the  cervical  sympathetic  ;  it  reacts  on  the  pupil,  on  certain 
vessels,  and  on  certain  glands. 

Connexions  with  the  oculo-motor  nerves. — The  motor  nerves  of  the 
eye  are  also  connected  with  the  great  sympathetic  ;  from  it  they 
receive  slender  branches  which  are  destined  for  the  vessels  of  the  muscles 
which  they  supply  ;  further,  by  means  of  the  oculo-motor,  they  give 
to  it  more  than  they  receive  from  it,  because  it  is  through  it  that  the 
thick  and  short  branch  is  furnished  which  is  one  of  the  roots  of  the 
ophthalmic  ganglion,  and  which  represents  the  constrictor  nerve  of  the 
pupil.  The  long  and  slender  branch  which  is  supphed  by  the  ophthalmic 
division  is  its  dilator  nerve. 

Connexions  with  the  hypoglossal. — At  the  other  extremity  of  the 
meduUa  oblongata  the  connexions  of  the  hypoglossal  are  established 
with  the  superior  cervical  ganglion,  which  supplies  it  with  a  very 
obvious  anastomosis  and  one  whose  function  is  weU  defined  (con- 
strictor nerve  of  the  vessels  of  the  tongue).  On  the  other  hand,  the 
hypoglossal  supplies  few  or  no  original  elements  to  the  great  sympa- 
thetic (experiment  does  not  reveal  their  presence). 

Ganglionic  elements  of  the  facial. — In  the  interval  which  separates 
the  hypoglossal  from  the  trifacial  pair,  the  relations  of  the  great 
sympathetic  with  the  facial,  the  glosso-pharyngeal  and  the  pneumo- 
spinal  nerves,  appear  to  be  altogether  interrupted.  Yet  these  rela- 
tions exist,  but  in  order  to  demonstrate  them,  it  is  once  again  necessary 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    165 

to  resort  to  experiment.  The  facial  sends  to  three  of  the  gangha  of 
the  trigeminal  three  important  branches  :  the  two  superficial  petrosal 
nerves  (large  and  small)  for  the  spheno-palatine  and  otic  ganglia,  and 
the  chorda  tympani  for  the  submaxillary  ganglion.  It  is  obvious  that 
these  branches  act  on  the  vessels  (dilatory  nerves)  and  on  the  glands 
(secretory  nerves)  of  the  corresponding  localities.  They  are  then 
origins  of  the  great  sympathetic,  which  must  be  added  to  those 
referred  to  above. 

Geniculate  ganglion  :  its  nature. — It  is  usually  considered  that  these 
three  branches  arise  from  the  nerve  of  Wrisberg  through  the  inter- 
mediation of  the  geniculate  ganglion.  The  question  to  be  determined 
is  if  this  ganglion  is  purely  sensory,  or  whether  it  is  mixed  in  function. 
Even  for  the  ganglia  of  the  posterior  roots,  this  question  is  not  abso- 
lutely settled.  According  to  Onodi,  the  ganglia  of  the  great  sym- 
pathetic and  the  spinal  ganglia  take  origin  in  immediate  proximity 
the  one  to  the  other,  and  are  only  separated  afterwards  ;  is  it  possible 
that  a  portion  of  the  first  remains  incorporated  in  the  mass  of  the 
second  ?  This  question  may  be  propounded,  but  it  has  not  been 
answered. 

Ganglion  of  Andersch  :  Jugular  and  Plexiform  Ganglia. — The  glosso- 
pharyngeal and  the  pneumogastric  nerves  pass  through  ganglia, 
to  which  may  confidentl}^  be  attributed  the  sensory  nature  of  the 
spinal  ganglia  ;  but,  it  being  admitted  that  these  two  nerves  have 
important  vaso-motor  and  secretory  functions,  and  that  they  possess 
these  functions  from  their  origin,  it  is  probable  that  these  ganglia  are 
also  mixed,  that  is  to  say,  half  sensory  like  the  spinal  ganglia,  half 
motor  of  the  vegetative  life,  like  those  of  the  great  sj^mpathetic. 

1.   Nerves  of  Special  Sense 

Those  organs,  and  therefore  those  nerves,  are  called  seyisoYial,  which 
subserve  the  special  senses  other  than  the  tactile  sensibility,  known 
as  general.  This  convention  might  lead  to  the  supposition  that  the 
tactile  sense  is  only  an  element  common  to  the  other  senses,  which 
represent  it  merely  in  a  differentiated  condition.  As  a  matter  of 
fact,  touch,  properly  so  called,  is  itself  a  sensation  differentiated  in 
a  special  direction.  That  which  earns  it  the  name  of  general  sensi- 
bility is  not  its  more  simple  physiological  modification,  but  its  more 
extensive  anatomical  distribution.  Just  as  the  other  senses,  it  also 
presents  numerous  gradations. 

Amongst  the  nerves  of  special  sense,  or  sensorial  nerves,  there  are 
some  which  in  the  medulla  oblongata  really  reproduce  the  arrange- 
ment of  a  posterior  root  ;    such  are  the  glosso-pharyngeal  and  the 


166 


SYSTEMATIC  FUNCTIONS 


auditory,  which  have  nuclei  of  origin  analogous  to  those  of  the  tri- 
geminal, itself  the  bulbar  nerve  of  touch  ;  but  there  are  others,  such 
as  the  olfactory  and  especially  the  optic,  whose  morphology  has 
entirely  broken  away  from  this  arrangement  of  nerve  roots.  These 
nerves  are  in  reality  tracts  of  the  spinal  cord  or  of  the  brain  pro- 
longed to  the  neighbourhood  of  the  organs  of  sense  (neurons  of  pro- 
jection of  the  second  degree),  at  the  extremity  of  which  grey  matter  is 
found  (retina),  and,  arising  from  the  latter,  microscopical  nerve  elements 
(rods,  cones),  which  represent  neurons  of  the  first  or  peripheral  order. 

a.     Olfactory  Nerve 
This  name  must  be  limited  to  the  collection  of  nerve  filaments  which 
creep  in  the  pituitary  mucous  membrane,  and  are  prolonged  to  the 


Saso-p'ilaiive      Int.  branch  of 
N.  the  olf.  N. 


Oil   Hnlb 


F.thmoid  F. 


Deep  hranch  of  the 

ethinoid  i.racl. 


Fig.   69. — Branches  of  the  olfactory  nerve. 
This  figiire  only  shows  the  branches  which  are  distributed  to  the  internal  sui'face  of  the  nasal 
fossa  (after  Hirschfeld). 


olfactory  bulb,  by  passing  through  the  perforations  of  the  cribriform 
plate  of  the  ethmoid.  These  bundles  have  no  ganglion  in  their  course, 
but  their  fibres  take  origin  from  cells  which  have  persisted  in  the 
olfactory  mucous  membrane,  together  with  epithelial  elements  which 
cover  the  latter.  This  is  an  arrangement  which  is  common  to  the 
neurons  of  special  sense,  and  distinguishes  them  from  the  neurons  of 
general  sensation.  This  arrangement  is,  further,  that  usually  found 
as  regards  the  nerves  of  sensation  in  the  invertebrata. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    167 

It  is  allowed  without  dispute  that  the  olfactory  nerve  is  the  con- 
ductor of  olfactory  impressions,  and  that  it  is  the  only  conductor 
thereof.  Yet  its  function  has  been  caUed  in  question  by  Magendie, 
who  beheved  that  the  sense  of  smell  was  preserved  in  animals  after 
he  had  destroyed  the  olfactory  bulb.  The  sense  of  smell  would  then 
have  appertained  to  the  fifth  pair,  whose  filaments  are  distributed  in 
the  nasal  mucous  membrane,  together  with  those  of  the  olfactory 
nerve.  But  the  substance  which  was  made  use  of  (annnonia)  was  an 
irritating  vapour  which  acted  on  the  terminations  of  the  nerve  of 
touch ;  and  this  explains  the  evidences  of  disgust  which  the  animals 
evinced.  On  the  other  hand,  section  of  the  trigeminal  induced,  after 
a  certain  period,  trophic  changes  in  the  sensory  apparatus  to  which 
branches  of  this  nerve  are  distributed.  Hence  result  secondary  sen- 
sorial paralyses  or  pareses,  which  are  the  result  of  a  mechanism 
entirely  different  from  that  which  causes  paralyses  or  pareses  of  the 
sensorial  nerve  itself,  but  which  may  be  attributed  to  the  latter  if 
this  circumstance  is  not  taken  into  account. 

CI.  Bernard,  Le  Bee,  Testut  liave  ascertained  the  absence  of  the  olfactory  bulb 
and  the  olfactory  tract  (formerly  known  as  the  olfactory  nerve)  in  persons  in 
whom  the  sense  of  smell  was  present  diiring  life.  Le  Bee's  case  has  been  sub- 
mitted by  M.  Duval  to  histological  investigation.  This  author  has  ascertained, 
on  the  one  hand,  the  presence  in  the  pituitary  membrane  of  olfactory  filaments  ; 
and,  on  the  other,  in  the  brain,  the  existence  of  a  real  olfactory  tract ;  whence 
the  conckision  follows  that  the  intermediate  conductors  must  have  been  present, 
although  following  an  abnormal  covirse. 

b.  Optic  Nerve 
Just  as  the  olfactory  tract  must  not  be  described  by  the  name  of 
olfactory  nerve,  so  the  optic  nerve  should  no  longer  be  regarded  as 
l^eing  the  extended  link  between  the  retina  and  the  brain  passing 
through  the  chiasma,  but  only  the  neurons  which  directly  receive  the 
luminous  impression  and  communicate  it  to  the  ganghonic  elements 
of  the  retina.  In  the  limited  thickness  which  separates  the  retinal 
surface  from  these  ganghonic  cells  two  superposed  layers  of  neurons 
maybe  defined  :  (1)  the  rods  and  the  cones,  (2)  the  bipolar  cells ;  and 
there  is  a  discussion  as  to  whether  it  is  the  first  or  the  second  which 
represents  the  sensory  nerve  of  vision,  and  which  is  therefore 
equivalent  to  the  neurons  of  the  posterior  roots  in  the  exercise  of  the 
sense  of  touch.  The  function  of  these  elements  must  not  be  sepa- 
rated from  that  of  the  retina,  to  which  we  shall  several  times  have 
to  return. 

c.     Auditory  Xerve 
The  auditory  nerve  suggests,  far  more  than  the  preceding  forma- 


1(;8  SYSTEMATIC  FUNCTIONS 

tions,  the  typical  arrangement  of  an  ordinary  sensory  nerve.  It  is 
massed  together  into  a  trunk  which,  from  the  internal  ear,  is  distri- 
buted to  the  lateral  portions  of  the  medulla  oblongata,  it  runs  side  by 
side  with  the  facial  nerve  and  the  intermediary  nerve  of  Wrisberg  in 
the  interosseous  portion  of  its  journey  through  the  internal  auditory 
canal.  Like  the  other  nerves  of  special  sense,  it  has  nevertheless  its 
cells  of  origin  at  the  periphery,  in  the  ganglia,  included  in  the  interior 
of  the  special  apparatus  of  the  sense  of  hearing.  In  reality  this  nerve 
is  double,  and  corresponds  to  two  distinct  functions  :  that  of  audition 
or  reception  of  sounds  by  a  special  apparatus  contained  in  the  cochlea 
and  that  of  the  reception  of  special  impulses  connected  with  the  idea 
of  movement  or  of  fosition  in  space  by  another  equally  special  apparatus 
contained  in  the  semicircular  canals.  One  is  the  cochlear  nerve,  the 
other  the  vestibular  nerve  ;  the  cells  of  origin  of  the  first  are  situated 
in  the  ganglion  of  Corti  or  spiral  ganglion  ;  those  of  the  second  in  the 
ganglion  of  Scarpa. 

d.  Nerves  of  Taste 
The  elements  of  the  gustatory  special  sense  are  contained,  as  regards 
their  greater  portion  (base  of  the  tongue  and  isthmus  of  the  throat) 
in  the  glosso-pharyngeal^  and  as  regards  a  smaller  part  (tip  of  the 
tongue)  in  the  chorda  tympani,  a  branch  of  the  facial  mixed  with 
elements  whose  functions  are  diverse.  Their  experimental  study  is 
included  in  that  of  the  nerve  trunks. 

2.  Sensory  and  Motor  Nerves 
In  a  first  natural  group  are  included  the  motor  nerves  of  the  eye, 
namely  :  the  oculo-motor  (3rd  pair),  the  pathetic  (4th  pair),  the  ex- 
ternal oculo-inotor  (6th  pair)  ;  then  important  and  complicated  nerves 
like  the  trigeminal  (5th  pair),  the  facial  (7th  pair),  the  glosso-pharyngeal 
(9th  pair),  the  vagus -or  pneumogastric  (10th  pair),  the  spinal  accessory 
(11th  pair),  the  hypoglossal  (12th  pair).  As  applied  to  the  cranial 
nerves,  the  expression  "  nerve  pair  "  is  devoid  of  all  physiological 
signification,  in  the  sense  of  that  which  is  given  to  it  in  the  case  of 
the  spinal  nerves  (union  of  a  sensory  and  motor  root)  ;  it  simply 
describes  the  two  nerves  which  are  symmetrically  detached  from  the 
medulla  oblongata  at  the  same  level. 

a.     Oculo-motor 
The  oculo-motor  nerve  supplies  the  levator  palpebrae  superioris,  and 
in  addition  four  (out  of  the  six)  of  the  muscles  of  the  eyeball,  namely, 
the  superior  rectus,  the  internal  rectus,  the  inferior  rectus,  and  the 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS     109 

inferior  oblique.  Paralysis  of  this  nerve  is  rendered  evident  by  ex- 
ternal strabismus  (a  non-compensated  contraction  of  the  external 
rectus),  and  a  displacement  of  the  eye  both  downwards  and  inwards, 
together  with  a  slight  rotation,  due  to  the  superior  oblique.  Down- 
ward and  upward  movements  are  impossible.  The  dipper  eyelid  falls 
on  account  of  the  predominant  action  of  the  orbicularis  palpebrarum. 

Borrowed  sensory  elements. — The  oculo-motor  nerve  receives  an 
anastomotic  fibre  from  the  ophthalmic  branch,  which  is  of  sensory 
function  (muscular  sense). 

Original  ganglionic  elements. — At  its  origin  this  nerve  includes  tlie 
highest  root  of  the  great  sympathetic.  It  separates  from  it  in  the 
form  of  a  thick  and  short  filament,  which  proceeds  to  the  ophthalmic 
ganglion  and  thence,  by  the  ciliary  nerves,  to  the  muscular  apparatus 
of  the  iris  and  to  that  of  accommodation.  In  addition,  therefore,  to 
the  movements  of  the  muscles  referred  to  abos^e,  stimulation  of  the 
oculo-motor  causes  contraction  of  the  iris  and  protrusion  of  the 
crystalline  lens.  The  antagonistic  action  (dilatation  of  the  iris  and 
flattening  of  the  crystalline)  is  effected  by  the  slender  branch  of  the 
nasal  nerve,  which  originally  arises  either  from  the  great  sj'^mpathetic 
or  from  the  trigeminal  itself.  The  oculo-motor  nerve  receives  gang- 
lionic elements  not  only  through  its  proper  roots,  but  also  by  its 
anastomoses  with  the  chain  of  the  great  sympathetic  properly  so  called. 

b.     External  Oculo-motor  and  Pathetic 

The  external  oculo-motor  is  distributed  to  the  external  rectus 
muscle  ;  its  paralysis  causes  internal  strabismus.  The  pathetic  is 
distributed  to  the  superior  obUque  ;  its  paralysis  is  followed  by  a 
deviation  of  the  globe  of  the  eye  upwards  and  outwards. 

The  oculo-motor  nerve  alone  of  the  motor  nerves  of  the  globe  of 
the  eye  appears  to  supply  branches  of  origin  to  the  cranial  ganglia 
of  the  great  sympathetic,  but  all  receive  from  this  nerve  branches  of 
distribution  which,  without  any  doubt,  are  destined  for  the  vessels 
of  the  muscles  of  the  eye. 

Sensory  elements. — All  the  motor  nerves  of  the  eye  are,  on  the 
other  hand,  in  an  anastomotic  relation  with  the  ophthalmic  branch, 
as  much  by  recurrence  near  to  their  extremities,  as  directly  at  the 
level  of  the  cavernous  sinus.  These  sensory  elements  are  destined 
for  the  ocular  muscles,  whose  degree  of  contraction  they  estimate  and 
measure,  so  that  it  may  be  proportioned  to  the  movement  about  to 
be  undertaken. 

c.     Facial 
The  facial  nerve  arises  from  the  medulla  oblongata  by  two  roots  : 


170  SYSTEMATIC  FUNCTIONS 

the  one  larger,  motor  ;    the  other  very  small  {pars  intermedia  of  Wris- 


Oeiilo-  Er  oculO' 

nuitor  N  motor  A 


Inj.  max.    Opiu.    .bup.         Spfieii.         UplU.  In/.     CiUary  bub.  orb. 

N.  N.      max.  Pal.  G.    obliq.  Branches  N. 

N.  G.  Branch 

Fig.   70. — rrincipal  nerves  of  the  eye,  motor,  sensory,  sensorial  and  ganglionic.    Their 

anatomical  relations. 
Ophthalmic  ganglion  ;    direct  and  indirect  ciliary  nerves. 

herg),  terminating  in  the  ganglion  {geniculate   ganglion),  situated    on 
one  of  the  angles  of  the  nerve  in  its  transit  through  the  intrapetrous 


■  Svp.  ocitlo-motor  Br. 


Cav.  plez. 


Br.  of  orijin 
oi  the  eir  it.  plexus. 


Sup.  cervical  O. 


Irido-constrict.  Fibres. 
.Contract.  Fibres  of  the  ciliary  muscle. 
„  Vaso-constrict.  fibres  of  the  eye. 

Irido-dilating  fibres. 
,  Relaxing  fibres  of  the  ciliary  muscle. 
.  Vaso-dilating  fibres  of  the  ant.  segm.  of  (he  e««. 


Fig.   71. — Constitution  of  the  ophthalmic  ganglion  (diagram  after  Cuneo). 

portion  of  the  temporal  bone,  and  which  would  appear  to  be  sensory. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    171 

The  facial  has,  further,  vegetative  sensori-motor  functions  resembling 
those  of  the  great  sympathetic  :  this  nerve  was  the  S7nall  sym'patJipMc 
of  older  observers. 


--.  Right  inf  nbliqne. 
Ophthal.  O. 
—  ^  Oc.  iiiolor. 

Frontal  .V. 

^ Lachrymal  }J. 


■<iip.  max.  S. 
..,-'•,    Men.  br.  of 


Inf.  max. 


Men.  br.  of 
inf  max.  Hf. 

Fig.   72. — Principal  nerves  of  the  eye  and  their  anastomoses. 

More  especially,  branches  of  the  superior  inaxiUary  branch  of  the  trigeminal  proceeding  to  the 
dura  mater. 


Intracranial  Section. — The  facial  nerve  may  be  cut  in  several  ways  ;  the  follow- 
ing method  is  preferable  :  an  incision  is  made  behind  the  ear  and  the  space 
between  the  condyle  and  the  superior  curved  line  of  the  occipital  bone  is  laid  bare. 
Then  the  occipital  bone  is'perforated,  being  very  thin  in  this  locality'.  The 
neurotome  slides  along  the  petrous  portion  to  the  internal  auditory  meatus, 
where  the  nerve  is  cut  (necessarily  also  the  auditory  nerve). 

Intracranial  section  of  the  nerve  thus  effected  reproduces  the 
symptoms  of  paralysis,  at  the  same  time  'peripheral  and  deep,  of  the 
facial  nerve. 

A.  Peripheral  Portion. — The  paralysis  known  as  peripheral  is 
that  which  involves  the  muscles  of  the  face  when  the  section  of  the 
nerve  is  effected  (experimentally  or  pathologically)  at  its  exit  from 
the  skull  at  the  stylo-mastoid  foramen.     These  muscles,  inserted  by 


172 


SYSTEMATIC  FUNCTIONS 


one  of  their  extremities  in  the  skin  of  the  face,  produce  in  the  latter, 
or  disturb   in    it,  certain    folds,  and  give   to  the  physiognomy  that 


Te  np.  Branch 


I  III    Wri.fberg. 

N.  to  the  stapes 

Chorda,  tympani 

Br.  ant.  glusso. 

Br.  to  the  vagus. 

Post  auric.  N. 

Dij.  N. 

Linjua'  R. 

Cervio-facial  br. 


Te.np.  branch. 


Front  and  sup. 
P'llp.  branches. 


I   Sup.  palp.  br. 


Great  and  small  sup. 
petrosal  N. 


Sub.  orbital  br. 


Sup.  buccal  br. 


j  Inf.  buccil  br. 

Ment.  br. 

\ ..     Cervical  br. 

Fig.   73. — Diagram  of  the  facial  (after  Cuneo). 
The  terminal  branches  are  in  black,  the  collateral  branches  in  grey. 


particular  expression  which  externally  displays  each  of  our  emotions. 
Hence  the  facial  is  known  as  the  nerve  of  expression. 

In  addition  to  these  distinctive  or  emotional  junctions,  there  are 
other  voluntary  functions,  as  we  can  easily  prove  on  ourselves  ;  there 
are  also  purely  reflex  or  automatic  functions,  such  as  the  closure  of 
the  eyelids  which  is  effected  by  the  orbicularis  on  the  threatened 
entrance  of  a  foreign  body,  the  dilatation  of  the  nostrils  which  accom- 
panies each  inspiration,  the  movements  of  the  lips  which  accompany 
mastication. 

1.   Deviation    of    the  features. — In  unilateral  paralysis,  the  loss  of 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    173 


muscular  tone  on  the  side  corresponding  to  the  paralysis  causes  a 
drawing  over  to  the  opposite  side  by  the  non-paralysed  muscles. 
Owing  to  the  paralysis  of  the  orbicularis,  the  eye  remains  wide  open. 
Paralysis  of  the  buccinator  muscle  causes  the  cheek  to  be  distended 
at  each  expiration,  which  is  expressed  by  the  saying  that  the  patient 
is  smoking  a  pipe  (/wme  le  pi'pe).  The  ear,  but  only  in  animals,  drops, 
in  consequence  of  the  weakness  of  some  of  the  external  muscles. 

When  the  paralysis  is  bilateral,  the  face  resembles  a  mask. 

2.  Elements  of 
general  sensation  : 
sensation  by  recur- 
rence and  by  anas- 
t  o  m  o  s  i  s  .  —  The 
peripheral  portion  of 
the  facial  contains 
elements  of  general 
sensation.  If,  after 
having  cut  this  nerve 
at  its  exit  from  the 
stylo-mastoid  fora- 
men, its  peripheral 
and  central  ends  are 
successively  pinched, 
it  will  be  noticed 
that  both  are  sensi- 
tive ;  the  first  by 
recurrence  of  the 
fibres  of  the  trigemi- 
nal, whichform 

plexuses  with  the  terminal  branches  of  the  facial  ;  the  second  by 
anastomosis  of  the  branch  arising  from  the  jugular  fossa  (auricular 
branch  or  nerve  of  Arnqjd)  of  the  pneumogastric,  which  thus  supplies 
some  sensory  fibres  to  the  facial  nerve  (CI.  Bernard). 

B.  Deep  Portion. — The  deep  portion  of  the  facial  is  represented  by 
branches  which  it  supplies  in  its  transit  through  the  petrous  portion, 
or  immediately  on  its  exit  from  this  bone. 

1.  Motor  Elements. — As  regards  the  motor  function,  paralysis  of 
these  branches  (the  result  of  intra-cranial  section  of  the  nerve)  is 
rendered  evident  by  a  difficulty  of  sicallowing,  by  a  nasal  tone  of  voice 
and  by  a  deviation  of  the  uvula  to  the  side  opposite  to  that  paralysed. 
The  difficulty  of  swallowing  is  due  to  the  paralysis  of  the  digastric, 
and  of  the  stylo-hyoideus,  and  also  of  the  palato-glossus  and  of  the 


/Jt     c 


Fig.   74. — Superficial  nerves  of  the  head  in  the  dog  (after 
Ellenberger  and  Bamn). 

a,  facial  ;  b,  posterior  auricular ;  c,  internal  auiieuiar  ; 
d,  branch  of  the  digastric  ;  e,  inferior  buccal  ;  /,  superior  trans- 
verse cervical  ;  g,  zygomatico-temporal  branch  of  the  facial  ; 
h.  superior  buccal  ;  i,  its  temporal  branch  ;  k,  its  zygomatic 
branch  ;  k\  its  branch  for  the  lower  eyelid  ;  k" ,  for  the  upper 
eyeUd  ;  I,  superficial  temporal  ;  m,  malar  or  parotid  branch  ; 
n.  buccinator  ;  o,  branch  of  the  mylo-hyoid  ;  p>  orbital  branch 
of  the  superior  maxillary  ;  q,  lachrymal ;  r,  frontal  :  s,  sub- 
trochlear  ;    t,  sub-orbital. 

1,  styloid  apophysis  ;   2,  digastric  ;    3,  pinna  of  the  ear  ;  4, 
masseter  ;   5,  large  zygomatic  :   6,  scutellar  ;   7,  zygomatic  arch 
8,  superior  maxillary. 


174  SYSTEMATIC  FUNCTIONS 

palato-pharyngeus,  the  nasal  tone  of  the  voice  to  that  of  the  levator 
palati  ;    the  deviation  of  the  uvula  to  that  of  the  azygos  uvulae. 

The  fibres  which  proceed  to  the  soft  palate  and  to  its  pillars  are 
conducted  thither  by  the  posterior  palatine  nerves,  which  proceed 
from  the  geniculate  ganglion  by  the  intermediation  of  the  large  super- 
ficial petrosal  nerve,  and  of  the  spheno-palatine  ganglion.  It  is  a 
question  whether  these  nerves  are  not  closely  united  to  these  ganglia, 
or  whether,  as  Longet  holds,  they  actually  form  a  component  part 
of  them.  The  exact  origin  of  the  motor  nerves  of  the  soft  palate  is 
not  clearly  known. 

2.  Sensory  elements. — The  soft  palate  receives  for  its  pillars  some 
sensory  gustatory  elements  which  come  to  it  through  the  palatine 
branch  of  the  nerve  of  Wrisberg  (Vulpian). 

3.  Ganglionic  elements  :  superficial  petrosal  nerves. — The  facial 
contains  a  notable  proportion  of  nerves,  really  ganglionic  (vegetative 
in  function),  which  it  derives  from  its  own  origins  (small  root,  nerve 
of  Wrisberg).  The  same  palatine  nerve,  which  has  just  been  con- 
sidered, like  the  great  superficial  petrosal  7ierve  which  gives  rise  to  it, 
contains  secretory  elements  destined  for  the  glands  of  the  mucous 
membrane  of  the  soft  palate  ;  it  also  contains  vaso-dilator  fibres  for 
the  same  structure.  The  vaso-constrictor  fibres  are  distributed  to  it 
by  the  filament  of  the  great  sympathetic,  which  is  closely  united  to 
the  large  petrosal  in  order  to  form  the  Vidian  nerve.  The  small  super- 
ficial petrosal,  which  from  the  facial  proceeds  to  the  otic  ganglion,  is, 
as  regards  its  function,  but  imperfectly  known. 

Deep  petrosal  nerves. — The  great  and  small  superficial  petrosal  nerves  each 
receives  from  t'he  glosso-pharyngeal,  by  Jacobson's  branch,  an  anastomotic 
branch,  which  is,  as  regards  the  first,  the  small  internal  deep  petrosal  and,  as 
regards  the  second,  the  small  external  deep  petrosal.  The  function  of  the  first 
is  but  little  known  ;  the  second  contains  secretory  and  vaso-dilator  elements  of 
the  parotid  gland.  Leaving  the  glosso-pharyngeal,  they  then  follow  a  branch 
of  the  facial  ;  having  passed  through  the  otic  ganglion,  they  enter  the  auriculo- 
temjsoral  branch  of  the  inferior  maxillary  and  then  pass  into  the  parotid.  Thus 
the  glosso-pharyngeal  and  the  facial  both  take  part  in  the  A'aso-motor  and  secre- 
tory innervation  of  the  salivary  glands  and  of  the  soft  palate.  This  is  proved 
by  stimulating  these  two  nerves  at  their  cranial  origin  (Vulpian). 

Branch  to  the  muscle  of  the  stapes. — The  facial  supplies  a  small 
branch  which  proceeds  in  the  middle  ear  to  the  muscle  of  the  stapes. 
Its  action  is  antagonistic  to  that  of  the  filament  to  the  internal  muscle 
of  the  malleus,  which  takes  origin  in  the  trigeminal  ;  it  relaxes  the 
membrana  tympani  and  lowers  pressure  in  the  labyrinth. 

Chorda  tympani. — An  anastomotic  branch   extends  from  the  facial 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    175 

to  the  lingual  and  skirts  the  internal  surface  of  the  membrana 
tympani  ;  for  this  reason  it  is  known  as  the  chorda  tympani.  Dis- 
tributed to  the  tongue,  to  the  sub-maxillary  and  to  the  sub-lingual 
glands,  this  branch  is  vaso-dilator  as  regards  these  three  organs  ;  it 
is  secretory  in  function  for  the  two  glands.  We  shall  see  a  little 
further  on  that  this  important  branch  also  contains  centripetal 
elements.  With  the  two  superficial  petrosal  nerves  it  is  regarded  as 
the  principal  continuation  of  the  small  root,  or  nerve  of  Wrisberg. 


5  Jl*  V  V      .; 


Great  sup.  petrosal  N. 

Small  iitp  pelrosil  N. 


^~r~^^\      Spheno- 

pnl.  ganjlion. 

Inf.  dent.  A'. 

Gln<isn  phart/njeal  N. 
(  hordi  tympani  If. 

Lingual  M. 


Fig.  75. — Deep  branches  of  the  facial. 

More  especially  the  chorda  tympani ;    the  superficial  petrosal  nerves,  the  branches  of  the 
Styloid  muscles  and  their  anastomosis  with  the  glosso-pharyngeal. 


C.  Origins. — This  analysis,  which  is  effected  as  we  ascend  from  the 
periphery  to  the  centre,  leads  us  to  the  origins  of  the  facial  nerve, 
these  being  formed  by  the  trunk,  properly  so-called,  of  the  seventh 
pair,  or  the  larger  root,  and  the  nerve  of  Wrisberg,  or  the  smaller  root. 

I ntra-cra7iial  excitation.  The  isolated  stimulation  of  the  two  roots 
of  the  facial  (even  after  the  skull  has  been  opened)  is  not  easily  effected. 
But  at  least  we  may  inquire  if  in  either  of  the  elements  general  sensa- 
tion be  present.  CI.  Bernard  denies  this,  basing  his  opinion  on  the 
fact  that  this  stimulation  was  painless,  while  the  root  of  the  trigeminal 
of  the  same  animal  was  very  sensitive. 


176 


SYSTEMATIC  FUNCTIONS 


Meckel's  G. 


Vid.  N. 

Great  sup.  pet.  n. 

Small  sup.  pet.  n. 

ot.  G. 

Chorda  tyin. 

Jacobs  iV. 

Glosso-pharyi^ 


V 


Hence   the  elements  of  ordinary  sensation  will  be  present  in  very 

small  number.  On 
the  other  hand, 
this  stimulation 
brings  into  action, 
tolerably  easily, 
the  voluntary  and 
involuntary  motor 
elements  which 
have  been  c  o  n- 
sidered  above. 

Gustatory  Sense. 
— The  opinion 
which  has  p  r  e- 
vailed  concerning 
the  function  of 
the  small  root  of 
the  facial  or  nerve 
o  f  Wrisberg  i  s, 
that  it  represents 
an  aberrant  origin 
of  the  gloss  o- 
pharyngeal  nerve, 
which  is  destined  for  the  tip  of  the  tongue  by  the  path  of  the  chorda 

tympani,  and  for  the  soft  palate  by  the 
large  superficial  petrosal  nerve  and  the 
posterior  palatine  nerve,  which  is  one 
of  its  branches  of  continuation.  Its 
bulbar  nucleus  appears,  indeed,  to 
continue  the  nucleus  of  the  ninth  pair 
above  and  in  front  (M.  Duval,  Vul- 
pian). 

Intracranial  paralysis  of  the  facial 
and  section  of  the  chorda  tympani  are 
accompanied  with  a  marked  diminu- 
tion  of  taste  at  the  tip  of  the  tongue  and 
of  the  jnllars  of  the  soft  palate . 


Pneumogas. 


Cervico-faciil  br. 


Fig.  76.-— Diagram  of  the  anastomoses  of  the  facial  with 
the  trigeminal,  the  glosso-pliaryrgeal,  and  the  pneumo- 
gastric.     Superficial  and  deep  petrosal  nerves. 

The  colours  do  not  represent  function.?,  but  merely  anatomical 
nervous  groups. 


Fig.   77. — Sensory     areas     of     the 
branches  of  the  trigeminal. 

The  area  of  the  ophthalmic  in  red  ; 
that  of  the  superior  maxillary  in  yel- 
low ;  that  o  the  inferior  maxillary  in 
blue. 


Secretory  and  Vaso-dilatory  Action. — As 
regards  movement,  intracranial  stimulation 
of  the  facial,  besides  the  contraction  of  the 
muscles  of  the  face,  of  the  digastric,  of  the 
stylohyoid  of  the  tensor  palati,  of  the  azygos 
uvulae  muscle,  etc.,  induces  secretion  of  the  sub-maxillary  and  sub-lingual  glands. 


SENSATION  AXD  MOTION— THEIR  RELATIONSHIPS    177 

as  also  of  those  of  the  soft  palate  ;  it  causes  congestion  of  these  same  organs 
and  of  the  mucous  membrane  of  the  tongue  and  of  the  soft  palate. 

Indirect  action  on  several  senses. — Thus  the  facial  is  directly  coiuiected  with 
the  sense  of  taste,  at  least  as  regards  the  tip  of  the  tongue  and  the  soft  palate. 

But  its  paralysis  may  also  induce,  in  a  roundabout  way,  disorders  of  the  other 
senses.  The  eye  is  deprived  of  its  protective  %vinking  of  the  eyelid  ;  neverthe- 
less it  does  not  become  inflamed  as  it  does  after  section  of  the  trigeminal.  One 
of  the  muscles  of  the  middle  ear  is  paralysed.  The  sense  of  smell  is  itself  em- 
barrassed by  the  absence  of  dilatation  of  the  nostrils  and  by  paralysis  of  the 
palate  (Longet). 

Mixed  nature  of  the  geniculate  ganglion  and  of  the  nerve  of  Wrisberg. — The 
geniculate  ganglion  has  been  sometimes  described  as  a  gangUon  of  the  great 
s\Tnpathetic,  sometimes  as  a  spinal  ganglion,  and  those  who  hold  one  of  these 
opinions  reject  the  other  ;  they  are  not.  however,  incompatible,  and  it  is  probable 
that  the  nerve  of  Wrisberg  contains  both  vegetative  elements  and  those  wliicli 
are  sensitive,  or  rather,  sensorial,  as  is  the  case  with  tlie  posterior  spinal  roots 

d.  Trigeminal. 
The  sensory  distribution  of  the  trigeminal  corresponds  to.  the  whole 
of  the  face  (including  the  forehead),  as  also  the  corresponding  cavities 
(this  distribution  is  that  of  its  sensory  or  ganglionic  root).  It  causes 
contraction  of  the  raasseter.  temporal,  internal  and  external  pterygoid 
and  mylo-hyoid  muscles,  \\hich  take  an  essential  part  in  the  act  of 
mastication  (this  function  appertains  to  its  small  root,  motor  root, 
masticatory  root  of  Bellingeri). 

Intracranial  section  of  the  trigeminal. — Intracranial  section  of  the  trigeminal, 
the  animal  sm-viving,  was  first  performed  bj'  Magendie,  and  it  has  become  one 
of  the  classical  operations  of  neurologj*.  It  is  easily  performed  in  the  rabbit, 
in  which  the  cranial  walls  are  tliin,  and  may  be  effected  also  in  the  dog.  The 
neurotome  made  use  of  has  a  fine  blade  ending  in  a  triangle,  which  is  adapted 
both  for  pricking  and  cutting  ;  with  this  the  cranial  wall  is  perforated  in  the 
middle  temporal  fossa  immediately  beliind  the  condyloid  tubercle  of  the  lower 
jaw.  "Wlien  the  instrument  is  once  in  the  skull  it  is  directed  against  the  anterior 
face  of  the  petrous  portion  of  the  temporal  bone,  at  the  point  where  tlie  depression 
in  wliich  the  trigeminal  with  its  ganglion  is  situated.  The  instrument  is  then 
turned  downwards,  and  is  at  the  same  time  withdrawn  in  order  to  catch  the 
nerve  and  to  cut  it  by  the  steel  triangle  in  which  the  neurotome  ends.  At  tliis 
instant  the  animal  ^^tte^s  cfies.  and  the  eyeball  protrudes. 

A.  Sensory  and  motor  functions. — Anatomically  considered,  the 
trigeminal  has  the  constitution  of  a  spinal  pair  :  this  view  is  verified 
in  every  way  by  experiment. 

Sensory  paralysis. — After  section  of  the  fifth  pair,  it  is  found  that 
the  cornea,  the  conjunctiva,  the  tongue,  the  skin  of  the  face,  and  the 
mucous  membranes  of  these  cavities  are  insensible  on  the  side  operated 
on,  except  as  regards  their  deeper  portion  where  the  distribution  of 
the  trigeminal  is  mingled  with  that  of  other  nerves.     The  ear  remains 

p.  N 


178 


SYSTEMATIC  FUNCTIONS 


sensitive  on  account  of  the  important  branches  which  it  receives,  both 
from  the  cervical  plexus  and  the  pneumogastric. 

Borrowed  sensorial  element. — Isolated  section  of  the  lingual  nerve 
causes  the  disappearance  in  the  tip  of  the  tongue  both  of  general 
sensation  and  of  the  sense  of  taste.  But  while  the  tactile  elements  of 
this  area  arise  from  the  origins  of  the  trigeminal,  its  gustatory 
elements  are  supplied  to  it  by  the  nerve  of  Wrisberg  by  the  aid  of  the 
facial  and  of  the  chorda  tympani. 

Motor  paralysis. — If  both  trigeminals  are  divided,  mastication 
becomes  impossible.     If  the  section  is  unilateral,   inasmuch  as  the 


Fio.   78. — Diagram  of  the  ophthalmic  nerve  and  of  its  branches. 

two  halves  of  the  lower  jaw  form  a  consolidated  whole,  mastication 
may  stiU  be  partially  effected  by  means  of  the  muscles  of  the  intact 
side  ;  but  the  jaw  is  deviated  and  drawn  to  the  sound  side  ;  the  teeth 
no  longer  correspond  ;  one  incisor  of  the  upper  jaw  opposes  a  single 
incisor  of  the  lower  ;  the  two  others,  being  no  longer  kept  in  place  by 
mutual  opposition  and  regular  use,  grow  unduly  long. 

Intracranial  excitation. — If  the  roots  of  the  trigeminal  in  the  skull 
be  exposed,  direct  excitation  will  show  that  the  large  root  is  endowed 
with  acute  sensibility,  while  the  small  root  is  m,otor  for  the  m,uscles  of  the 
jaw  (masseter,  temporal,  internal  and  external  pterygoid,  and  mylo- 
hyoid). 

B.  Connexions  with  the  great  sympathetic. — Like  all  the  nerve 
trunks  proceeding  from  the  spinal  cord  or  the  medulla  oblongata,  the 
trigeminal  contains  elements  originating  in  the  great  sympathetic,  and 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS     179 

receives  branches  of  distribution  from  this  nerve.  These  sensori-motor 
elements  (of  sub-conscious  sensation  and  of  involuntary  movement) 
fulfil  very  diverse  functions,  aU  of  which  relate  to  the  connexions 
between  organs,  and  which  on  this  account  have  a  bearing  on 
nutrition. 

Secretory  elements. — To  speak  here  only  of  the  secretory  elements, 
the  trigeminal  supplies  these  to  the  lachrymal  gland,  to  the  sudoriparous 
glands  of  the  face,  and  to  the  eye  itself  for  the  regulation  of  its  internal 
tension  ;  they  proceed  to  it  either  from  the  cranial  sympathetic,  or 
from  its  own  origins.  It  furnishes  secretory  elements  to  the  glands 
of  the  velum  palati  and  to  the  submaxillary  and  sublingual  glands, 


Genie,  gang 


N.  to  mm.  nf  stave 


Chorda-tympam 


Post-aunc  N 


^^ 


.w^^ 


0.^'' 


Opht.  N. 

Sup.  max.  Jf. 

N.  to  Int.  mus.  mil. 

Otic.  G. 

Chorda  tympani. 

Auric,  temp.  N. 
Lingual  N. 

f.  dental  N. 


Fig.   79. — Innervation  of  the  muscles  of  the  ossicles  and  chorda  tympani. 

Internal  muscle  of  the  malleus  receiving  a  branch  of  the  trigeminal  nerve  through  the  otio 
ganglion.     Muscle  of  the  stapes  receiving  a  branch  of  the  facial. 


which  come  to  it  from  the  nerve  of  Wrisberg.  It  supplies  the  same 
to  the  parotid  and  the  molar  gland,  the  so-called  gland  of  N  tick,  which 
proceeds  to  it  from  the  glosso-pharyngeal,  A\ithout  its  origins  or  the 
cranial  sympathetic  taking  any  part.  But  the  nerve  of  Wrisberg  and 
the  glosso-pharyngeal  take  some  part,  like  the  pneumogastric,  in  the 
formation  of  the  ganglionic  system.  The  vaso-dilator  elements  of  the 
same  organs  have  the  same  origin.  Generally  speaking,  the  con- 
strictors are  supphed  from  the  cervical  sympathetic. 

C.  Trophic  disturbances. — Intracranial  section  of  the  trigeminal 
reacts  in  different  ways  on  the  nutrition  of  the  face  in  a  more  or  less 
direct  or  indirect  manner.     Magendie  observed  that,  after  section  of 


180 


SYSTEMATIC  FUNCTIONS 


this  nerve,  the  eye  loses  its  briUiancy  and  its  polish.  The  change, 
which  is  visible  some  hours  only  after  the  operation,  usually  com- 
mences in  the  centre  of  the  cornea  in  the  form  of  a  spot  which  pro- 
gressively becomes  more  and  more  opaque.  At  the  same  time  a  kind 
of  cloud  appears  in  the  anterior  chamber.  And  after  some  days 
an  invasion  of  the  cornea  by  a  vascular  network,  which  starts  from 
its  edge  and  stops  abruptly  at  a  certain  distance  from  its  centre,  may 
be  seen.  In  the  case  of  weak  or  badly  nourished  animals,  destruction 
of  the  eye  may  ensue  through  perforation  of  the  cornea  and  escape 
of  the  crystalline  lens  and  of  the  humours  (CI.  Bernard).  In  certain 
cases  Magendie  observed  the  gangrene  to  extend  to  the  whole  of  the 
face. 


Sphen.  Nas.   Front.  Tact, 
pal  G.    A".        N. 


Orbito-lachrymo  arc. 


PImryn.  N. 
Has.  pi!.  N. 

Post.  pal.  N. 

Middle  pa! 
Ant.  pal.  N. 


Sub-orbit   N. 


Ant  dent.  N. 


Pout.  dent.  N. 


Midd'e  dent.     Dent. 
N.  Plexus. 


Fig.   80. — Diagram  of  the  superior  maxillary  nerve  and  its  branches. 

Their  contingency. — In  man,  trophic  disturbances  of  the  eye 
analogous  to  those  which  have  been  described,  though  less  severe, 
have  been  several  times  observed  to  ensue  after  lesions  of  the  tri- 
geminal nerve.  However,  these  troubles  do  not  appear  of  necessity, 
and,  especially  in  surgical  intracranial  section,  they  have  been 
moderated  or  avoided.  It  must  not  be  forgotten,  horweve,  that  the 
vulnerabihty  of  the  parts  deprived  of  their  nerve  supply  is  increased, 
and  that  these  disturbances  may  thus  appear  under  the  influence  of 
ordinary  and  sometimes  slight  causes. 

Different   locality.— Magendie,  CI.  Bernard,  all  those  who  consecu- 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    181 

tively  to  them  have  performed  intracranial  section  of  the  trigeminal 
nerve  on  animals,  have  often  observed  ulceration  of  the  upper  and 
lower  lip  and  changes  in  the  conjunctiva,  as  also  in  the  naso-buccal 
mucous  membrane,  affecting  the  vascularization  and  secretion  of  these 
surfaces. 

Photophobia. — When  the  eye  is  inflamed,  especially  the  iris  and  the 
cornea,  a  particularly  painful  sensitiveness  to  light  arises,  which  com- 
pels the  patient  to  avoid  luminous  rays  by  closing  the  eyelid.  Although 
light  is  the  irritant,  the  origin  of  this  painful  sensation  does  not  lie 
in  the  retina.  Photophobia,  indeed,  may  occur  in  amaurosis,  in  which 
the  visual  sense  no  longer  exists.  When,  in  animals,  the  optic  nerve 
has  been  previously  cut,  a  wound  of  the  cornea  induces  photophobia 
(CI.  Bernard,  Castorani).  Photophobia  does  not  occur  when  the 
conjunctiva  is  alone  inflamed. 

The  iris  seems  to  possess  a  special  sensitiveness  to  light,  and  can 
contract  directly  under  the  influence  of  luminous  rays  (Brown-Sequard). 
The  sensitiveness  of  the  cornea  is  supplied  by  the  ciliary  nerves  known 
as  indirect,  which  pass  through  the  ophthalmic  ganglion  ;  that  of  the 
iris  by  both  the  direct  and  indirect  ciliary  nerves  (CI.  Bernard). 

Ophthalmic  ganglion  :  its  nature. — Certain  authors  have  discussed  the 
question  whether  the  ophthalmic  ganglion  (which  some  call  also  ciliary 
ganglion)  is  the  equivalent  of  a  sympathetic  or  of  a  spinal  ganglion. 
It  is  probable  that  its  sympathetic  functions,  very  definitely  elicited 
by  experiment,  are  not  exclusive  of  conscious  sensory  functions,  of  the 
kind  of  those  possessed  by  the  ganglionic  root  of  the  trigeminal,  of 
which  it  would  represent  an  aberrant  mass  of  very  small  dimensions. 

In  man,  a  complete  sensory  paralysis  of  the  trigeminal,  with  the 
exception  of  the  cornea,  has  been  observed  ;  this  would  be  explained 
by  an  alteration  of  the  nerve  not  involving  the  ophthalmic  ganglion 
(Thesis  of  Demaux,  1843). 

Classification  of  the  elements. — In  all  these  complicated  nerve  trunks 
forming  the  cranial  nerves,  experiment  demonstrates  the  existence  of 
three  orders  of  elements  :  some  sensory  or  of  special  sense,  others 
motor,  others  which  are  known  as  ganglionic  or  of  the  great  sympathetic. 
Fundamentally,  these  latter  are  also  sensory  and  motor  elements,  but 
of  a  special  order  ;  they  have  a  double  anatomical  and  physiological 
character.  The  neurons  which  compose  them,  instead  of  proceeding 
from  a  single  point  of  the  spinal  cord  to  the  organs,  are  interrupted  in 
their  course  by  the  grey  matter  of  the  ganglia  ;  and,  on  the  other 
hand,  their  sensitiveness  is  obscure  and  their  motor  power  automatic, 
that  is  to  say,  involuntary. 

The  different  disturbances  mentioned  above  agree  with  those  of  the 

N* 


182 


SYSTEMATIC  FUNCTIONS 


elements  of  diverse  functions  originally  contained  in  the  trigeminal, 
or  yielded  to  its  branches  of  distribution  by  the  anastomoses  which 
come  to  it  from  the  great  sympathetic  :  vaso-motor  elements,  secre- 
tory elements,  together  with  other  elements  whose  nature  is  but 
ill-determined. 

Vaso-motor  elements. — The  trigeminal  contains  vaso-motor  elements 
supplied  to  it  by  the  great  sympathetic  and  whose  origins  are  in  the 
second,  third,  fourth  and  fifth  roots  of  the  dorsal  spinal  cord.  Some 
of  these  elements  are  of  constrictive  and  others  of  dilatory  function  as 
regards  the  vessels  of  the  face  (Dastre  and  Morat).  They  are  unequally 
distributed  in  its  different  regions  or  cavities  (see  Great  Sympathetic). 


Mid.  deep  temp.  N. 

'-■■Opht.  X. 
-.  Sup.  max.  N. 
Ant.  deep  temp.  X 


Inf  dent.  A'. 
Mylu-hyoid  N. 


Digasi.  Er. 


Fig.   81. — Diagram  of  the  inferior  maxillary  nerve. 

They  regain  the  trunk  of  the  fifth  pair  by  passing  chiefly  by  the 
anastomosis  which,  from  the  superior  cervical  ganglion,  proceeds  to 
the  Gasserien  ganglion.  A  section  made,  either  through  this  last 
ganglion,  or  in  front  of  it,  interrupts  the  continuity  of  these  elements 
and  explains  the  vascular  disorders  which  are  the  consec^uence  of  this 
section  in  the  deep  and  superficial  portions  of  the  eye,  as  also  in  the 
nasal  mucous  membrane  and,  in  a  lesser  degree,  the  mucous  membrane 
of  the  mouth. 

(a)  Constrictor  elements. — The  great  sympathetic  supplies  constrictor 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    183 

elements,  both  to  the  branches  and  to  the  trunk  of  the  trigeminaL 
The  retina,  the  bucco-facial  region  receives  branches  from  it  through 
the  anastomosis,  which  proceeds  from  the  superior  cervical  ganglion 
to  the  Gasserien  ganglion.  The  anterior  segment  of  the  eye  seems  to 
receive  them  by  a  route  which  is  independent  of  this  anastomosis 
(Morat  and  Doyon). 

(b)  Dilator  elements. — The  cranial  prolongation  of  the  great  sym- 
pathetic, which  proceeds  from  the  superior  cervical  ganglion  to  the 
Gasserien  ganglion,  contains  the  larger  portion  of  the  dilators  supplied 
by  the  great  sympathetic  to  the  trigeminal  (Morat). 

Elements  whose  function  is  undetermined. — The  tropliic  disturbances  of  the 


Lachrym.  S, 


Temp.  Br. 


J/o'.  Br. 


—  Inf.  Br.  of  00. 
motor. 


Sub.  orbit.  iV. 


H 

PnH.      Midil'd  "'-'"^ 

dent.       de.it.     BucctI  faciil 
^V.  .V.  Br. 


Fig.    82. — Superior  maxillary  nerve  :    its  superficial  branches. 

eye  and  of  the  face  which  ensue  consecutively  to  the  section  or  paralysis  of  these 
nerve  trunks  are  not  satisfactorily  explained  either  by  the  fact  that  sensation 
is  abolished,  or  by  the  circumstance  that  the  circulation  has  been  disturbed,  or 
even  because  these  parallel  alterations  of  sensibility  and  of  blood  supply  occur 
concruTently.  INIany  authors  have  considered  this  a  proof  that  there  must  be 
in  the  nervous  system  particular  elements,  regulating  in  a  specific  manner  the 
cellular  nutrition,  and  which,  for  this  reason,  they  call  trophic  nerves. 

Position  of  the  question. — Presented  in  this  manner,  the  question  is  not  well 
propounded,  and  it  is  necessary  to  recast  it  in  its  proper  aspect.  That  cellular 
activity  is  dominated  by  the  nervous  system  is  a  fact  which  is  perfectly  clear 
and  incontestable  ;  but  this  acti\'ity  presents  itself  under  diverse  aspects  ;  it  is 
resolvable  into  multiple  phenomena  having  between  them  bonds  of  dependence. 
We  assert  in  principle  that  the  nervous  system  does  not    intervene  in  a  separate 


184  SYSTEMATIC  FUNCTIONS 

manner  as  regards  each  of  these  phenomena  by  distinct  elements,  but  that  it  merely 
supplies  to  the  cell  that  initial  impulsion  tvhich  causes  them  to  display  themselves 
in  the  order  which  is  imposed  upon  them  by  their  serial  arrangement. 

Typical  example. — As  a  definite  example,  we  may  take  a  muscle.  When  the 
nerve  of  this  organ  is  stimulated  it  manifests  :  ( 1 )  an  elimination  of  heat, 
(2)  apparent  movement,  (3)  interchanges  of  its  substance  with  the  blood  which 
passes  through  it.  The  bond  of  imion  between  all  these  internal  and  external 
phenomena  is  in  itself  so  evident  that  we  do  not  attribute  them  to  three  orders 
of  nerves,  which  would  be  distinguished  according  to  each  one  of  these  special 
ijhenomena,  but  to  a  single  order  of  fibres  whicli  we  call  motor,  in  accordance 
with  the  most  obvious  phenomenon  and  that  longest  known,  which  results  from 
their  stimvilation.  These  phenomena,  in  their  totality,  are  often  massed  together 
under  the  name  of  nutrition,  which  implies  an  exchange  of  substance  and  of 
energy  with  the  medivmi  which  makes  good  the  waste  due  to  muscular  work. 

Degeneration. — It  must  be  added  that  it  is  not  a  matter  of  indifference  whether 
a  muscle  receives  stimulations  or  is  dej^rived  of  them,  whether  it  acts  normally 
or  is  condemned  to  a  definite  repose.  Absokite  privation  of  stimulation  induces 
an  alteration  of  the  composition  and  of  the  intimate  structure  of  the  muscular 

cell. 

Tliis  structural  change  is  known  as  degeneration  or  trophic  alteration  when  it 
has  become  marked  in  the  muscle  element  which  has  continued  too  long  inactive. 
The  motor  nerve  which  presides  over  the  chemical  and  molecular  phenomena 
which  bring  about  these  consequences  is  thus  at  one  and  the  same  time,  a  nerve 
of  movement,  a  nerve  of  heat  production,  a  nerve  of  chemical  metabolism,  and 
a  nerve  of  nutrition.  Every  nerve  which  has  an  influence  on  any  one  cell,  in 
the  sense  of  arousing  it  to  its  specific  activity,  exerts  by  this  very  fact  a  control 
over  a  series  of  analogovis  or  equivalent  phenomena  which  follow  one  another 
in  the  same  order,  and  of  which  some  are  immediate  and  others  remote.  On 
the  other  hand,  these  phenomena  may  not  be  equally  visible  ;  the  first  (func- 
tional phenomena)  owing  to  their  very  nature,  may  in  certain  cases  elude  our 
observation,  while  the  latter  (structm-al  alterations)  are  necessarily  obvious. 

Function  which  is  not  visible  externally. — Tliis  is  probably  what  happens  as 
regards  organs,  such  as  the  skin  and  the  cornea,  whose  fixed  cells,  epithelial  or 
otherwise,  have  a  wholly  internal  activity  which  is  not  manifested  in  any  case 
by  visible  movement.  Doubtless  this  activity  is  controlled  by  nerves  in  a  manner 
similar  to  that  of  the  glands  ;  only  the  stimulation  of  these  nerves  has  no  directly 
visible  effect  ;  while  the  definite  loss  of  this  activity,  consecutive  to  the  sup- 
pression of  these  nerves  is  shown,  after  some  time,  by  the  alterations  which  are 
its  usual  result. 

Conclusion. — The  skin  and  the  cornea  possess  no  other  trophic  nerves  than  those 
which  preside  over  the  functional  activity  of  their  elements.  The  details  of  this 
activity  elude  our  actual  methods  of  observation.  It  can  only  be  said  that  the 
cessation  of  this  activity  reveals  itself  by  a  structural  disorder,  the  result  of  the  loss 
of  nutritive  equilibriuin. 

Functional  analogies. — If  this  explanation  is  admitted,  if  the  existence  of 
centrifugal  nerves  proceeding  to  the  fixed  elements  of  those  tissues  which  are 
still  considered  to  be  deprived  of  such  an  innervation  is  accepted,  their  elements 
should  take  their  place  alongside  those  which  terminate  in  the  glandular  cells. 
The  epithelia  known  as  those  of  investment,  whose  function  is  certainly  not 
limited  to  that  of  mechanical  protection,  which  is  the  one  attributed  to  it,  are 
just  as  much  entitled  as  the  glands  to  be  excited  and  directed  in  their  functional 
activity  by  impulses  distributed  by  the  nervous  system.  These  centrifugal 
nerves,  analogous  to  the  secretory  nerves,  belong,  without  any  doubt,  like  the 
Jatter,  to  the  ganglionic  system. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS  :  185 

Section  of  the  posterior  roots,  trophic  disturbances. — Section  of  the  posterior 
lumbar  and  sacral  roots  often  indvices  in  the  corresponding  posterior  limb  ulcera- 
tions, witli  falling  off  of  the  nails  and  tlie  hair  of  this  region,  thickening  of  the 
skin  witli  hypertrophy  of  the  metatarsal  bones  and  phalanges.  These  facts 
resemble  those  which  follow  section  of  tlie  trigeminal  nerve.  Like  the  trigeminal, 
the  posterior  roots  of  this  region  contain  sensory  elements,  and  amongst  them 
centrifugal  elements  whose  vaso-dilator  function  with  regard  to  the  correspond- 
ing limb  has  been  demonstrated.  But  here  again  the  trophic  disturbances  do 
not  seem  to  be  in  constant  relationship  with  the  modifications  of  sensation  and 
of  vascularization.  Hence  here  once  more  the  existence  of  centrifugal  elements 
must  be  allowed,  elements  which  are  no  longer  destined  merely  for  the  vessels,  but 
also  for  tlie  tissues  of  the  skin,  and  wliicli  also  belong  to  tlie  ganglionic  system. 

D.  Indirect  action  on  the  senses. — The  trigeminal  distributes 
its  ramifications  in  the  four  cavities  of  the  face  containing  the  organs  of 
the  four  important  senses  :  the  orbital  cavity  (vision),  the  nasal  cavity 
(sense  of  smell),  the  cavity  of  the  mouth  (taste),  the  auricular  cavity 
(hearing).  All  these  sensory  organs  are,  as  it  were,  enclosed  in  a  field 
of  general  sensation,  whose  territory  belongs  to  it  (the  trigeminal). 
The  tactile  sense  is  thus  indirectly  called  upon  to  render  assistance 
to  the  complicated  functions  of  the  superior  senses. 

The  trigeminal  takes  part  in  tlie  exercise  of  these  senses,  not  only  by  its  sen- 
sory elements,  bvxt  also  by  the  involimtary  motor  elements  which  appertain  to 
it,  both  as  regards  its  origins  and  its  anastomoses  with  the  great  sympathetic. 
Without  speaking  of  the  vaso-motor  elements  which  regulate  the  circulation  in 
all  these  oi'gans,  it  takes  part  in  a  series  of  reflexes  of  adaptation  and  defence  of 
"wliich  the  principle  may  here  be  inentioned. 

a.  Vision. — The  ophthalmic  ganglion  supplies  ciliary  nerves  to  the  eye,  some  of 
which  are  constrictors,  the  others  dilators  of  the  pupil  ;  tlie  first  come  from  the 
oculo-motor,  the  second  from  the  trigeminal,  which  recei^^es  them  both  from  the 
great  sympathetic  and  from  its  origins.  The  first  act  chiefly  by  increasing  the 
eurvatm-e  of  the  lens,  and  thus  by  accommodating  the  eye  to  near  vision  ;  the 
second  act  in  the  opposite  manner,  namely,  by  diminishing  the  curvature  and 
accommodating  it  to  distant  vision  (Morat  and  Doyon). 

Intraocular  tension  is  maintained  in  its  normal  condition  by  a  kind  of 
equilibrium  between  the  internal  secretion  of  the  humours  of  the  eyeball  and 
the  depletion  of  the  latter. 

b.  Hearing. — -The  otic  ganglion  supplies  a  filament  to  the  middle  ear,  which 
proceeds  to  the  internal  muscle  of  the  malleus  and  regulates  the  tension  of  the 
membrana  tympani.  At  its  entrance  into  the  muscle,  this  branch  jjasses  through 
a  small  ganglion  which  is  the  equivalent  of  the  ciliary  plexus. 

c.  Smell. — ^Secretory  elements  of  the  spheno-palatine  ganglion  regulate  the 
degree  of  moisture  of  the  nasal  mucous  membrane. 

d.  Taste. — By  its  lingual  branch,  the  trigeminal  gives  off  an  important  branch, 
the  chorda  tympani,  which  controls  the  secretion  of  the  submaxillary  gland,  and 
by  it  the  condition  of  humidity  of  the  tongue  most  favoiu'able  to  the  sense  of 
taste.  The  chorda  tympani  is  a  borrowed  branch  which  comes  originally  from 
the  facial  and  ends  in  the  sub-maxillary  ganglion. 

e.     Glosso-pharyngeal. 
From  its  origins  the  glosso-pharyngeal  is  a  mixed  nerve ;  fibres  of 


186 


SYSTEMATIC  FUNCTIONS 


general  sensibility,  gustatory  fibres  and  motor  fibres  of  all  kinds  run 
side  by  side  in  it  in  radicular  bundles,  in  which  it  would  be  impossible 
to  separate  them  experimentally.  Yet  these  fibres,  whose  functions 
vary  so  greatly,  have  nuclei  of  origin  and  of  termination  which  are 
distinct  in  the  grey  bulbar  substance. 

1.  Section  :  Gustatory  paralysis. — Intracranial  section  of  the  glosso- 
pharyngeal nerve  cannot  be  performed  in  an  isolated  manner.  Section 
of  the  nerve  at  its  exit  from  the  skull  abolishes  gustatory  sensation 
in  the  posterior  portion  of  the  tongue,  that  is  to  say,  in  all  the  area 
situated  behind  the  lingual  V.  The  tip  of  the  tongue  receives  its 
sensory  fibres  from  the  lingual  trunk,  but  in  reality  by  the  inter- 


Jnenhann  N 

G.  «t  Aiiuer. 

Int.  nir^il 


Sup  cen  ic 
bymp.  0. 


Fig.   83. — Superior  maxillary  nerve  ;  its  branches  and  deep  anastomoses. 

mediation  of  the  chorda  tympani,  which  obtains  them  from  the  nerve 
of  Wrisberg. 

Sensory  paralysis. — Along  with  its  gustatory  fibres,  the  glosso- 
pharyngeal contains  elements  of  general  sensation.  Section  of  the 
nerve  at  its  exit  from  the  foramen  lacerum  is  painful,  and  its  excita- 
tion by  pinching  is  accompanied  with  cries  and  defensive  movements. 
The  ninth  pair  presides  over  general  sensibility  of  the  base  of  the 
tongue  and  partly  over  that  of  the  pharynx,  the  pharyngeal  plexus 
being  made  up  of  elements  coming  from  the  glosso-pharyngeal,  from 
the  vagus  and  the  great  sympathetic. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    187 

2.  Stimulation  within  the  skull. — By  the  stimulation  of  its  roots 
within  the  skull,  it  can  be  shown  that  the  glosso-pharyngeal  contains 
motor  elements  of  different  categories  from  its  very  origin. 

Animals  are  operated  on  which  have  just  been  killed,  the  animal 
employed  being  as  large  as  possible  ;  the  motor  power  in  these 
circumstances  persists  for  a  certain  time  after  every  kind  of  sensation 
is  extinct,  which  allows  a  sufficient  time  to  elapse  in  order  to  study 
it  and  eliminates  the  reflex  effects  which  might  be  due  to  sensation. 
Chauveau  has  observed  in  these  conditions  that  stimulation  of  the 
roots  of  the  glosso-pharyngeal  causes  contraction  of  the  inferior  con- 


SmnH  xnv.  pet.  n.  2V.  to  tensor  tympani. 

A  uric    temp. 


opht  .V.  -ji 

Sup.  max  N. 

Otic  G 
N.  to  tensor  palati. 


Chorda  tymp 
Int.  pteri/gind  .V 

Inf.  dent.  N. 


Lingual  .V. 


Chorda  tympani. 


Post,  auric.  X. 


Ext.  symp.  carot, 
plex. 


.■<>i>v;',;..', 


Mylo-liyoid  y 


Fig.   84. — Inferior  maxillary  nerve  (internal  aspect.) 


stridor  of  the  pharynx,  and  of  a  portion  of  the  muscles  of  the  soft  palate. 

Vaso-dilator  elements. — Just  as  the  gustatory  fibres  of  the  l-ngual 
and  of  the  chorda  tympani  are  accompanied  by  vaso-dilator  elements, 
so  also  are  those  of  the  glosso-pharyngeal.  By  stimulating  without 
or  within  the  cranium  the  ninth  pair  in  animals  whose  circulation  is 
intact,  Vulpian  has  observed  a  marked  congestion  at  the  base  of  the 
tongue  in  the  area  of  distribution  of  this  nerve.  There  is  also 
dilatation  of  the  parotid  vessels. 


188  SYSTEMATIC  FUNCTIONS 

Secretory  elements. — The  same  author  has  noticed  that  this  stimula- 
tion (made  within  the  skuU)  causes  the  parotid  glands  to  secrete.  By 
combining  this  result  with  those  previously  obtained  by  CI.  Bernard, 
Schiff,  etc.,  the  course  of  the  secretory  nerve  of  this  gland  is  found 
to  be  the  following  :  origin  of  the  glosso-pharyngeal,  the  ganghon  of 
Andersch,  Jacobson's  branch,  small,  deep  external  petrosal,  otic 
ganglion,  auriculo- temporal  branch,  of  which  certain  ramifications  are 
distributed  to  the  parotid. 

Ganglia  ;  their  functional  nature. — The  same  remark  may  be  made 
concerning  the  ganglia  of  the  glosso-pharyngeal  (ganglion  of  Ehren- 
ritter  and  ganglion  of  Andersch)  as  concerning  those  of  the  greater 
portion  of  the  cranial  nerves  ;  these  ganglionic  masses  are  without 
doubt  the  partial  equivalent  of  the  spinal  ganglia  of  the  posterior 
roots  (sensory  and  sensorial  fibres)  ;  but  it  is  probable  that  they  also 
represent  the  ganglia  of  the  great  sympathetic.  Jacobson's  nerve, 
which  is  given  off  by  the  ganglion  of  Andersch,  is  clearly  a  nerve  of 
vegetative  Ufe,  as  is  shown  by  its  connexions  with  one  of  the 
salivary  glands. 

f.     Pneumogastric 

The  pneumogastric  nerve  (still  called  the  median,  sympathetic,  vagus 
nerve,  or  nerve  of  the  tenth  pair),  ramifies  in  the  head,  neck,  thorax, 
and  the  abdomen,  that  is  to  say,  in  numerous  and  important  organs 
which  subserve  very  varied  functions.  It  includes  seiisory  and  motor 
elements,  both  of  the  life  of  relation  and  of  the  organic  life,  and  this 
from  its  very  origins  in  the  lateral  furrow  of  the  medulla  oblongata. 

A  Typical  arrangement. — In  the  constitution  of  the  metamere,  such  as  that 
which  corresponds  to  a  spinal  nerve  pair,  or  even  to  the  trigeminal,  the  separa- 
tion of  the  sensory  and  motor  functions  on  the  one  hand,  conscious  and  uncon- 
scious on  the  other,  affects  a  typical  arrangement  which  much  facilitates  the 
analysis  and  the  detailed  description  of  these  f mictions.  In  the  pneumogastric 
nerve,  this  externally  apparent  systematization  has  almost  disappeared,  through 
the  intermixture  and  intricacy  of  the  different  elements  after  leaving  their  place 
of  origin. 

Nucleus  of  origin. — The  nucleus  of  origin  of  the  tenth  pair  is  a  mixed  nucleus, 
enclosing  elements  whose  functional  value  differs  greatly.  It  receives  a  large 
number  of  centripetal  fibres,  among  which  the  elements  of  unconscious  sensation 
predominate,  along  with  fibres  of  conscious  sensation.  It  is  the  point  of  origin 
of  a  certain  mmiber  of  terminal  neurons  which  proceed  to  the  voliontary  muscles  ; 
it  gives  off  a  much  larger  mmtiber  of  which  the  terminations  are  arranged  in  a 
graduated  manner  in  the  ganglionic  masses  belonging  to  the  great  sympathetic, 
thus  showing  in  an  obvious  way  the  functional  relations  wliich  this  nerve  main- 
tains with  the  system  of  vegetative  life. 

Jugular  and  plexiform  ganglia. — At  its  exit  from  the  skull,  the  pneumogastric 
presents  two  ganglionic  enlargements  (jugular  ganglion  [ganglion  of  the  root]  and 
plexus  gangliforniis  [ganglion  of  the  trunk]),  which  their  structure  designates  as  the 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS      189 

•equivalents  of  a  spinal  ganglion,  at  least  as  regards  the  larger  portion  of  their 
•elements,  but  without,  nevertheless,  it  being  possible  to  affirm  that  they  do  not 
partially  correspond  to  a  great  sympathetic  ganglion. 

Field  of  distribution, — Taking  origin  in  the  medulla  oblongata  and  soon  anas- 
tomosing with  important  nerves,  among  which  is  the  spinal  accessory  which 
yields  to  it  its  internal  branch,  the  pneumogastric  exhausts  itself  in  ramifying  suc- 
■cessively  in  the  neck,  the  thorax  and  the  abdomen.  Its  inferior  limits  are  not 
well  determined  because,  falling  into  a  complicated  system  made  up  of  ganglionic 
relays  which  also  contain  fibres  passing  tlirough  them,  we  have  no  anatomical 
■or  experimental  method  wliich  is  well  adapted  to  determine  the  localities  in 
which  its  fibres  terminate  ;  these  terminations  being,  further,  arranged  in  a 
graduated  series  over  a  certain  number  of  these  relays.  The  pneumogastric  is 
formed  of  fibres,  some  of  which  are  myelinated,  others  non-myelinated.     These 


Great  sup.  pet.  xV.     Spheno.  pal.  Q. 
Tub.  br. 


Small  deep  petr.  n 
Great  deep.  petr.  n. 
Carol,  tymp.  Br. 


Br.  fen.  oi 

Br.  fen.  rot 

Jacobson  N 

O.  of  A  ndersch 

Spinal  ac 

Int.  jug.  rein 
Jhjp.  A 

Sup   cervic.  G 

Ext.  carat.  A 
3rd  cerv.  N 

Pneumog 


Glosso-pharyngeal  nerve  (after  Hirschfeld). 


latter  are  present  in  it  in  great  number,  and  the  former  are  in  it  much  reduced  in 
size.     These  characters  approximate  them  to  those  of  the  great  sympathetic. 

Protoneurons  and  intercentral  neurons. — The  elements  of  conscious  sensation 
and  of  voluntary  movement  which  the  pneumogastric  contains  are  confined  to 
the  neck  and  proceed  chiefly  to  the  larj-nx.  Hence  they  are  obedient  to  the  law 
of  metamerism,  which  demands  that  their  terminations  should  be  contained  in 
the  same  segment  of  the  body  as  that  which  includes  their  origins,  or  nearly  so. 
They  are  initial  or  terminal  neurons,  or  protoneurons.  On  the  other  hand,  the 
elements  of  unconsciovis  and  involuntary  function  break  altogether  with  meta- 
merism ;   in  doing  this  they  reproduce  the  arrangement  of  the  great  sympathetic 


190  SYSTEMATIC  FUNCTIONS 

chain,  wliich  forms  coinmixnications,  no  longer  between  the  organs  of  a  meta- 
mere,  but  between  the  different  metaraeres  themselves,  for  the  functions  as  a 
whole.  The  gi-eater  portion  of  the  fibres  of  the  pneumogastric  are  thus  equiva- 
lent to  intercentral  fibres,  which  connect  an  important  region  of  the  grey  axis 
(medulla  oblongata)  with  the  nuclei  directly  naotor  in  function,  of  organs  which 
are  essential  to  life  (ganglion  of  the  great  sympathetic). 

Specific  functions. — If,  in  the  pneumogastric,  the  line  of  division  between 
sensation  and  motion,  and  even  between  the  conscious  and  unconscious,  is  not 
obvious  at  first  sight,  there  is  another  which  concerns  the  specific  nature  of  the 
functions,  and  which  is  on  the  contrary  very  evident.  This  large  assemblage 
of  nerves  exhausts  its  ramifications  in  three  great  apparatus  :  that  of  respira- 
tion,  that  of  circulation,  and  tliat  of  digestion,  whicli  it  helps  to  individually 
govern,  and  also  to  mutually  harmonize  amongst  themselves,  in  union  with 
other  portions  of  the  great  sympathetic  system.  Yet  the  elements  of  specific 
functions,  apart  from  the  fact  that  they  are  each  of  them  of  different  modalities 
(centripetal,  centrifugal,  motor,  inhibitory,  secretory,  etc.),  before  they  attain 
their  ternninations,  are  mixed  in  the  branches,  which  often  contain  them  tmited 

Vdcia'.      -■  T  /■■--■-•'  Facial. 

Great  sup.  pet.n.  --    "'^jA."" '"',                                  ^_-A_    ''     ""-^'-  /""•  •'"/'•  "»"/• 

Small  deep  pet.  n.  -  "M»mT^>*'-^^~^;;5^,____^^^^^^^              ^^^T'>^o5=""~i-iCJ'"  '    "  ^«'"-  '"^^-  ^■^-  '^'*''^-  P'* 

Great  deep  pet.n.   i?^-&'-^^\^  ■  (^VP^'^-^^~~^-'-~^-N.pet..pr.min.(Ar»,\ 

Small  sup.  pet.  n.       -- «-  V ^^^^  Y  ^V ^-  V^t.  sup.  min. 


Y                \                                   y               yr^  G.  olicum. 
k                A                          ^~>J|  \-    -  Chorda  tympani. 

G.  of  A  ndersch.    ■  ■  — ^  \  a .A   . .  G.  petrosum. 


Chorda  tympani. 


Diagram  A.  Diagram  B. 

Fig.   86. — Diagram  of  the  terminal  branches  of  the  branch  of  Jacobson. 
A,  French  nomenclature  ;   B,  German  nomenclature. 

one  with  another.     Thus  we  are  forced  to  make  an  analytical  and  detailed  review 
of  them  in  connecting  them  only  with  their  chief  fvinctions. 

A.  Respiration. — Respiration  is  represented  in  the  vagus  by  the 
nerves,  some  centripetal,  others  centrifugal,  which  preside  over  very 
diverse  kinds  of  acts. 

Superior  laryngeal  branch. — The  upper  portion  of  the  larynx,  the 
arytseno-epiglottidean  folds,  the  epiglottis,  the  posterior  and  inferior 
portion  of  the  tongue,  derive  from  this  nerve  (chiefly  by  the  superior 
laryngeal  branch),  the  acute  sensibility  with  which  these  regions  are 
endowed,  and  which  gives  rise  to  the  expulsive  cough  following  the 
introduction  of  the  least  drop  of  liquid  falling  on  the  aperture  of  the 
glottis. 

The  trunk  of  the  vagus,  when  the  nerve  is  cut  in  the  region  of  the 
neck,  is  but  slightly  sensitive  ;  it  contains  nevertheless  a  large 
quantity  of  subconscious  sensory  elements  which  are  distributed  to 
the  inferior  portion  of  the  larynx  and  the  trachea  {inferior  laryngeal 
or  recurrent  nerve),  the  oesophagus,  the  pulmonary  tissue,  the  stomach, 
and  doubtless  also  the  intestine  and  the  liver. 

By  the  anastomosis  of  Galen,  which  connects  the  superior  laryngeal 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    191 

nerve  to  the  recurrent,  the  lower  portion  of  the  larynx  and  the  trachea 
receive  sensory  elements  from  the  first  of  these  nerves  (Philippeaux 
and  Vulpian  ;  Fr.  Eranck),  in  addition  to  those  which  they  receive 
from  the  second. 

Sensitiveness  of  the  different  portions  of  the  larynx. — The  great 
difference  which  exists  between  the  sensitiveness  of  the  superior  and 
the  inferior  portions  of  the  larynx  can  be  shown  experimentally  : 
water  injected  from  above  downwards  (upon  the  opening  of  the 
glottis)  gives  rise  to  a  loud  expulsive  cough  ;  when  injected  from 
below  upwards  (by  an  opening  made  in  the  trachea),  this  defensive 
reflex  does  not  arise. 

Dyspnoea. — No  more  than  it  suppresses  hunger,  does  section  of  the 
two  vagus  nerves  in  the  neck  do  away  with  the  necessity  of  breathing. 
On  the  contrary,  it  may  be  said  that  it  increases  that  necessity. 
Respiration  becomes  slower  and  deeper,  assuming  the  characteristics 
of  that  which  is  known  as  dyspnoea. 

Eeffcts  of  the  stimulation  on  the  respiratory  movements. — Stimula- 
tion of  the  superior  end  of  the  cut  vagus  hastens,  on  the  contrary,  the 
respiratory  rhythm,  and  this  so  much  the  more  as  the  stimulation 
itself  is  the  more  intense  ;  it  may  arrest  the  movements  of  the 
diaphragm  and  of  the  thorax,  either  in  inspiration  or  in  expiration, 
according  to  the  branches  excited,  or  according  to  the  gaseous  com- 
position of  the  blood.  This  arrest  is  due  to  a  tetanic  contraction  of 
one  of  the  two  orders  of  muscles,  combined  with  inhibition  of  those 
of  the  opposite  order. 

Reflex  sensibility  of  the  viscera. — Doubtless  the  vagus  nerve  repre- 
sents the  sensory  element  of  a  considerable  number  of  reflex  pheno- 
mena which  are  observed  as  regards  the  vegetative  functions,  and 
double  section  of  the  nerve  should  induce  in  the  latter  various  per- 
turbations ;  but  these  are  not  rendered  obvious  by  disorders  which 
are  immediately  visible  like  the  preceding. 

Recurrent  nerve. — ^\Vith  the  exception  of  the  cricothyroid,  which  is 
innervated  by  the  superior  pharyngeal  nerve,  all  the  muscles  of  the 
larynx  are  supplied  by  the  recurrent  or  inferior  laryngeal  nerve. 

Original  and  borrowed  elements. — The  pneumogastric  in  the  region 
of  the  neck  contains  a  large  number  of  fibres  which  take  part  in  very 
diverse  motor  functions  ;  these  fibres  come,  some  from  the  same 
origins  as  those  of  the  tenth  pair,  and  others  from  anastomoses  with 
the  neighbouring  nerves,  especially  the  spinal  accessory,  with  regard 
to  which  we  shaU  refer  to  them  again.  The  movements  of  dilatation 
which  the  glottis  performs  at  every  inspiration  must  equally  appertain 
to  the  pneumogastric,  for  they  persist  after  the  extirpation  of  the 


192 


SYSTEMATIC  FUNCTIONS 


Avcf.  A. 


Occip 
Spi, 


■Sup.  Inierc.  Vein 


(Esophag.  br. 


■Thoracic  gang 


.Inierc.  N.     _i§] 


Sup.  diaph.  A 


RciM  A 


Mreat  splanehnie. 


Pneumn.  (Right). 


Semi-lunar  O. 


Fig    87 — Pneumogabtiic 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS  193 


Ophthal 
Sup.  max.  '      j 

lAngual.  -  / ;; [^1 

Gl.  pharyn 
Int.  carot.  - 
Hypoglossa' 
Thyro-hyoid.  V 
Pharyngeal  pie  r 


-^  p  I  anal 

—  f  mtdiinjastnc. 

—  hit  tpin  br. 

•  Ext   <<pin.  Or. 

•  Eyp 

—  Ind  cervical. 
Sup  certic.  0. 


Ant.  gant.  plex. 

Right  pneiimog.  - 
Hepat 


Left  pobt  pulin  plex 


Left  pneumog 


S.  azygos  vtn. 


Fig.   88. — Left  pneumogastric. 


194 


SYSTEMATIC  FUNCTIONS 


Sup.  laryng.  N. 
{ext.  br.) 


spinal  accessory  ;  but  the  vocal  movements  of  the  larynx  (narrowing 
of  the  glottis  and  tension  of  the  vocal  cords)  are  then  suppressed 
(CI.  Bernard). 

Pulmonary  nerves  ;  motor,  inhibitory. — The  membrane  of  the 
trachea,  the  large  and  small  bronchi,  and  even  the  pulmonary 
vesicles  (according  to  some  authors),  contain  smooth  muscular  ele- 
ments (fibres  of  Reissessen),  whose  contractions  are  very  slow.  The 
pneumogastric  supplies  them  with  motor  elements  (WiUiams,  P.  Bert), 
and  also  with  inhibitory  elements  (M.  Doyen).  The  action  of  the  one 
causes  narrowing  of  the  pulmonary  passages  regarded  as  a  whole,  that 
of  the  others  permits  of  their  distension  under  the  influence  of  the 
very  feeble  pressure  of  the  air  which  they  contain.     In  order  to  make 

the  inhibitory  effect  apparent, 
a  device  must  be  made  use  of 
to  dissociate  the  two  effects. 
The  ordinary  effect  of  stimu- 
lation of  the  vagus  is  that  of 
narrowing  (motor  effect).  In 
the  case  of  an  animal  sub- 
mitted to  the  action  of  pilocar- 
pine, on  the  contrary,  the 
inhibitory  effect  or  that  of 
dilatation  is  the  one  which 
results. 

Vaso-motor  effects. — Section 
of  the  vagus  nerves  is  followed 
by  pulmonary  congestion,  so 
marked  as  to  be  of  the  nature 
of  red  hepatization.  The 
laryngeal  nerves,  especially  the 
superior,  contain  vaso-dilator 
and  secretory  fibres  for  the 
mucous  membrane  of  the  larynx  (Hedon). 

B.  Circulation. — The  vagus  supplies  both  centripetal  and  centri- 
fugal elements  to  the  heart,  whose  modes  of  action  are  so  character- 
istic that  they  are  cited  as  typical  examples  of  this  species  of 
functional  activity. 

Depressor  Branch. — In  the  rabbit,  the  vagus  possesses  a  branch  of 
sensory  nature  which  comes  to  it  from  the  heart  tissue,  and  which 
joins  it  in  the  angle  of  separation  which  the  superior  laryngeal  branch 
forms  with  it.  Stimulation  of  the  peripheral  end  of  the  cardiac  branch 
has  no  effect  on  the  heart,  but  that  of  the  central  end  reacts  on  the 


Ace.  laryn.  N. 

Mid.  lar.  N. 
(term,  br.) 


Inf.  lar.  N. 


Fig.  89. — Distribution  of  the  nerves  in  the 
human  larynx  (semi-diagrammatic)  (after 
Exner). 

Lateral  aspect.     The  thyroid  cartilage  is  sup- 
posed to  be  transparent. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS     195 

general  circulation  hy  loicering  the  aortic  arterial  pressure  through  a 
double  mechanism  :  the  stimulation  is  indeed  reflected,  on  the  one 
hand  on  the  elements  which  stop  the  heart,  whence  ensues  slowing 
of  the  beats  of  the  organ  ;  and  on  the  other  hand  on  the  vaso-dilators 
of  the  deep  areas,  especially  of  the  intestine,  whence  results  diminution 
of  the  resistance  which  opposes  the  flow  of  the  blood  in  the  general 
capillaries,  and  in  this  way  lowering  of  the  general  arterial  pressure 
(Ludwig  and  Cyon).  It  is  owing  to  this  phenomenon  that  the  nerve 
has  received  the  name  of  depressor. 

Thus  stimulation  of  the  depressor  nerve  is  followed  by  complex 
effects  ;  indeed,  it  acts  in  an  opposite  manner  on  certain  departments 
of  the  vascular  system  ;  thus,  while  it  causes  dilatation  of  the  intestinal 
vessels,  it  contracts  the  capillaries  of  the  skin,  which  effect  is  especially 
visible  when  the  auricular  artery  is  observed  (Dastre  and  Morat)  ;  but 
nevertheless,  the  chief  effect  is  a  general  lowering  of  arterial  pressure. 
The  depressor  nerve  regulates  arterial  tension. 

Cardio-inhibitory  elements. — The  stimulation  of  the  pneumogastric 
in  the  neck  (or  that  of  its  cardiac  branches)  stops  the  contraction  of  the 
heart  by  causing  diastole  of  the  myocardium.  This  is  the  first  example 
of  stoppage  of  action  arising  from  the  nervous  system,  or,  as  it  is  now 
termed,  of  inhibition,  which  has  been  observed  (Weber,  1845). 

According  to  the  intensity  of  the  excitation,  the  heart  is  either 
totally  arrested  or  only  slackened.  Stimulation  of  one  only  of  the 
two  vagus  nerves  suffices  to  produce  either  slowing  or  stoppage.  The 
inhibitory  action  of  the  right  vagus  is  usually  far  more  marked  than 
that  of  the  left  (Arloing  and  Tripier). 

Their  origin. — The  cardio-inhibitory  elements  contained  in  the  pneu- 
mogastric do  not  arise  from  the  origins  of  the  latter,  but  from  the 
internal  branch  of  the  spinal  accessory,  as  do  also  a  certain  number  of 
other  centrifugal  elements  of  the  tenth  pair.  They  originate,  there- 
fore, in  the  inferior  portion  of  the  medulla  oblongata. 

Cardio-accelerator  elements. — When  atropine  is  made  use  of  in  very 
small  doses  (less  than  a  milligramme),  paralysis  of  these  cardio-inhibi- 
tory elements  results,  which  are  then  no  longer  excitable.  Stimula- 
tion of  the  trunk  of  the  vagus  (in  which  the  action  of  these  fibres  has 
been  eliminated  by  this  means)  then  accelerates  the  heart  beats,  which 
proves  that  it  contains  a  certain  number  of  accelerator  elements  in- 
dependently of  those  which  are  supplied  to  the  heart  by  the  great 
sympathetic  (Fr.  Franck). 

Their  Origin  is  Distinct  from  that  of  the  Preceding. — If  the  trunk  of 

o* 


196  SYSTEMATIC  FUNCTIONS 

the  vagus  be  stimulated,  either  acceleration  or  slowing  of  the  heart 
may  ensue,  according  to  circumstances.  If,  on  the  other  hand,  the 
lower  portion  of  the  medulla  oblongata  be  stimulated,  after  the  latter 
has  been  separated  from  the  spinal  cord,  only  slowing  or  stoppage  is 
ever  seen  (Heidenhain).  Hence,  the  cardio-inhibitory  elements  arise 
from  the  medulla  oblongata,  while  the  cardio-accelerator  elements 
(even  those  contained  in  the  trunk  of  the  vagus)  take  origin  in  the 
spinal  cord. 

C.  Digestion. — Like  the  respiratory  apparatus  and  the  heart,  the 
digestive  tract  in  the  whole  of  its  upper  portion  derives  a  part  of  its 
innervation  over  a  large  area  from  the  pneumogastric.  Like  these 
same  apparatus,  the  nerve  supply  is  not  drawn  entirely  from  this 
nerve,  but  it  completes  this  supply  by  drawing  upon  a  portion  of  the 
great  sympathetic.  It  is  worthy  of  notice  that  the  nature  of  the 
action  exerted  by  each  of  these  nerves  on  each  of  these  apparatus  is 
different,  indeed  opposed,  inasmuch  as  the  one  is,  for  example,  in- 
hibitory, while  the  other  is  motor  for  a  given  organ.  Further,  it  is  to 
be  noticed  that  the  nature  of  the  action  of  each  nerve  is  not  univocal, 
each  of  the  two  nerves  being  motor  for  one  organ,  while  it  is  inhibitory 
for  the  other.  Also  the  functional  opposition  which  exists  between 
the  two  nerves  is  not  absolute  :  each  of  the  two  is  a  mixture  of 
antagonistic  fibres,  but  in  unequal  proportions. 

Pharyngeal  branch. — The  pharynx,  a  sensory  surface,  is  innervated 
by  the  pharyngeal  branch  concurrently  with  the  branches  of  the  ninth 
pair.  This  is  also  the  motor  branch  for  the  three  constrictor  muscles 
of  the  pharynx. 

Deglutition, — As  in  the  stomach  and  in  the  pharynx,  the  oesophagus 
receives  from  the  pneumogastric  both  sensory  and  motor  elements, 
which  take  part  in  the  performance  of  the  complicated  act  of  swallow- 
ing. Although  reduced  in  the  oesophagus  to  a  mere  movement  of 
peristaltic  propagation,  the  muscular  nervous  mechanism  which  is  its 
foundation  is  far  from  being  understood,  in  spite  of  the  experimental 
analysis  to  which  it  has  been  submitted  by  many  observers. 

In  the  dog  there  is  a  special  arrangement  :  the  superior  portion  of 
the  oesophagus  receives  its  nerves  from  a  branch  given  off  from  the 
superior  cervical  ganglion  of  the  sympathetic  (Espezel). 

Muscular  sensibility  of  the  oesophagus. — The  pneumogastric  gives 
sensory  nerves  to  the  oesophagus  ;  it  distributes  them  not  only  to 
the  mucous  membrane,  but  also  to  the  oesophageal  muscles,  whose 
movements  they  co-ordinate,  by  one  of  those  reflex  and  automatic 
acts  of  which  so  many  are  now  known. 

Part  taken  by  sensation  in  the  movements  of   the   oesophagus. — The 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS   197 

movements  of  the  oesophagus  are  almost  as  severely  disturbed  by 
section  of  its  sensory  fibres  as  by  that  of  its  motor  nerves.  Inde- 
pendent section  of  each  is  possible  in  certain  animals  for  a  given  area, 
of  the  tube,  at  all  events  to  a  certain  extent.  In  some,  indeed,  such 
as  the  horse,  the  ass,  the  dog,  the  sheep,  the  motor  fibres  which  are 
destined  for  the  cervical  portion  of  the  oesophagus  leave  the  vagus 
with  its  pharyngeal  and  external  largyngeal  branches  ;  while  the 
sensory  fibres  proceed  from  the  branches  given  off  lower  down.  In 
other  animals,  such  as  the  rabbit  and  possibly  man,  the  motor  elements 
attain  the  oesophagus  by  the  roundabout  route  of  the  recurrent 
(Chauveau).  Stimulation  of  the  sensory  fibres,  like  that  of  the  motor 
fibres,  causes  contraction  of  the  oesophagus,  but  does  not  give  rise  to 
the  peristaltic  action  which  is  its  normal  movement  ;  it  produces 
merely  a  more  or  less  complete  tetanic  contraction  of  its  muscles 
(Chauveau). 

Gastric  sensibility. — Seeing  that  the  pneumogastric  proceeds  to  the 
stomach,  it  has  been  asked  if  it  is  not  the  "  nerve  of  hunger,"  con- 
sidered thus  as  a  special  sensation  whose  external  field  would  be  the 
digestive  tube  (wholly  or  partially),  and  the  vagus  nerve  the  aggre- 
gation of  its  conducting  elements.  This  is  not  the  case  ;  after  section 
of  both  vagus  nerves,  an  animal  still  experiences  the  sensation  of 
hunger. 

General  needs. — Hunger,  like  thirst  or  the  need  of  breathing,  is  in 
realit}^  a  specialized  sensation  in  the  sense  that  we  can  define  it 
amongst  other  sensations  ;  but  the  field  of  excitations  which  give 
rise  to  it  is  (like  that  of  other  analogous  sensations)  more  or  less 
generalized  to  all  tissues  and  all  the  cells  of  the  organism.  Nutrition, 
to  which  it  corresponds,  is  not  indeed  confined  to  the  digestive  organs, 
but  is  a  general  fact  like  life  itself. 

Specific  nature  and  unconsciousness. — From  another  point  of  view, 
the  sensibility  of  the  gastric  mucous  membrane  seems  to  be  special 
and  connected  with  certain  acts  which  it  controls  and  provokes  ;  but 
this  sensibility  is  unconscious  or  sub-conscious  :  thus  the  injlorus  07ily 
opens  for  the  passage  of  aliments  into  the  intestine  ichen  gastric  digestion 
is  ended,  and  this  implies  a  sensory  phenomenon  which  might  by 
comparison  be  called  gustatory. 

Stimulation  of  the  origins  of  the  vagus. — Stimulation  of  the  roots 
of  the  vagus  nerve  causes  contraction  of  the  muscles  of  the  pharynx 
and  of  the  oesophagus,  and  at  the  same  time  induces  movements  in 
the  stomach  (Chauveau). 

Stimulation  of  the  Trunk. — Excitation  of  the  vagus  in  the  neck  gives 
every  facility  for  observing,  not  only  the  movements  of  the  stomach, 


198  SYSTEMATIC  FUNCTIONS 

which  are  the  consequence  of  it,  but  also  for  studying  their  character. 
These  movements  are  rhythmical,  as  is  shown  by  the  tracings  which 
can  be  obtained  of  them  by  placing  an  ampulla  in  the  gastric  cavity, 
and  they  are  doubtless  transmitted  in  a  peristaltic  manner  through 
the  length  of  the  organ  from  one  of  its  orifices  to  the  other.  The  line 
of  tracing  does  not  touch  zero  so  long  as  the  stimulation  lasts,  which 
indicates  a  continuous  pressure  exerted  by  the  stomach  on  its  contents. 

Thus  the  vagus  nerve  is  the  excito-motor  nerve  of  the  stomach,  but 
it  also  contains  some  inhibitory  elements  which  can  be  demonstrated 
in  a  reflex  manner,  by  exciting,  for  example,  the  central  end  of  the 
opposed  vagus  (Morat),  or  by  stimulating  a  nerve  of  general  sensation 
(Wertheimer). 

In  certain  animals,  stimulation  of  the  vagus  gives  rise  to  rhythmical 
contractions  of  the  upper  portion  of  the  intestine.  The  motor  effects 
are  mingled  with,  or  followed  by,  inhibitory  results.  A  vaso-motor 
influence  on  the  stomach  and  the  upper  portion  of  the  intestine  is 
also  recognized  as  belonging  to  the  pneumogastric  (Pingus). 

Secretory  elements. — Not  easily  demonstrated  as  regards  the 
stomach,  the  secretory  effects  of  stimulation  of  the  vagus  are  very 
definite  in  the  case  of  the  pancreas  (Afanasiew  and  Pawlow,  Morat). 
So  far  as  concerns  the  liver  (secretion  of  bile,  formation  of  sugar),  the 
action  of  the  tenth  pair  is  not  easy  to  determine.  Stimulation  of  the 
central  end  of  the  vagus  usually  causes  dilatation  of  the  sphincter, 
which  is  situated  at  the  extremity  of  the  bile  duct,  while  it  induces 
contraction  of  the  gall  bladder  (Doyen).  Stimulation  of  the  central 
end  acts  also  on  the  liver  by  augmenting  the  glycogenic  secretion 
(CI.  Bernard,  Filhene,  Laffont). 

Stimulation  of  the  peripheral  end  usually  diminishes  the  circulation 
in  the  kidney  and  the  secretion  of  urine  (Arthaud  and  Butte)  ;  it 
acts  equally  on  the  bladder,  by  making  it  contract  (Qi^hl).  By 
irritating  the  central  end,  Germain  See  and  Gley  have  induced 
azoturia. 


D.  Trophic  action. — Section  of  the  vagus  nerve  is  followed  by  very  various 
alterations  affecting  the  organs  which  are  supplied  by  this  nerve,  alterations 
which  affect  the  muscles,  the  mucous  membranes  and  the  parenchyma  of  these 
organs.  Atrojjhy  of  the  muscles  of  the  larynx  has  been  observed,  degenera- 
tions (but  limited  to  some  fibres)  of  the  myocardium,  haemorrhagic  and  inter- 
stitial lesions  of  the  gastric  mucous  membrane.  In  the  king,  especially,  emphy- 
sema, nuclei  of  congestion  and  of  red  hepatization  have  been  noticed ;  in  the 
kidney,  fatty  and  hyaline  degeneration.  Alongside  these  disorders  of  an  anato- 
mical nature,  others  have  been  met  with  which  the  chemical  study  of  the  organs 
and  of  the  media  have  brought  into  notice  :  namely,  a  diminution  in  the  gaseous 
exchanges  through  the  liuig,  a  diminution  of  the  hepatic  glycogen,  which  is  at 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS  199 

first  accompanied  with  a  hyperglycsemia,  afterwards  with  a  hypoglycsemia. 
These  disturbances  of  the  animal  chemistry,  which  it  is  the  custom  to  describe 
as  "  trophic,"  are,  fundamentally,  fiinctional  disturbances  of  organs  specially 
set  apart  for  the  purpose  of  general  nutrition  of  the  organism.  Tliis  sviffices  to 
show  that  the  expression  trophic  does  not  properly  characterize  them.  Specifi- 
cally, they  are  of  very  complicated  mechanism,  the  lesion  of  one  organ  reacting 
on  the  functional  activity  of  other  remote  organs  and  thus  inducing  new  altera- 
tions. 

Its  complex  mechanism. — When  the  vagus  nerves  have  been  cut,  and  in  this 
way  the  impulses  which  these  nerves  supply  to  certain  organs  have  been  abolished, 
tlie  initial  lesion  of  these  organs  belongs  to  the  order  of  degenerations  which 
follow  the  lack  of  functional  activity  (atrophic  degeneration  of  the  muscles, 
analogous  alteration  of  the  glands  of  the  parenchyma  and  of  the  epithelimu). 
These  disturbances  are  increased  by  the  circulatory  disorders  which  result  from 
the  section  of  the  vaso-motor  nerves  contained  in  the  pneumogastric.  The  func- 
tional inertia  which  is  at  the  foundation  of  these  degenerations  may  result  from 
the  depression  of  nervous  influences,  some  directly  motor  (the  ordinary  case), 
the  others  indirectly  motor  by  reflex  action  (the  case  of  atrophy  of  the  larynx 
which  ensues,  as  Exner  has  observed,  after  section  of  the  superior  laryngeal 
nerve,  a  nerve  pre-eminently  sensory). 

The  lesion  once  established,  when  it  is  located  in  such  an  organ  as  the  Ivmg 
disturbs  an  essential  function  :  hematosis.  A  certain  degree  of  asphyxia  results 
whose  usual  consequences  then  manifest  themselves.  Thej^  are  especially  shown 
by  the  prematiu-e  consumption  of  the  hepatic  glycogen,  by  hyperglycaemia,  and 
finally  by  hypoglycaemia,  \\\t\\  its  very  serious  consequences  (Couvreiir). 

Reaction  at  a  distance. — Important  organs  like  the  liver,  the  pancreas,  with- 
out speaking  of  the  kidney  and  the  digestive  tract,  are  in  a  way  attacked,  and 
directly  so,  by  the  suppression  of  the  relations,  both  centripetal  and  centrifugal, 
which  they  maintain  with  the  superior  centres,  and  indirectly,  by  the  alterations 
of  the  composition  of  the  blood,  on  which  they  themselves  regulate  their  own 
functional  activity.  Section  of  the  two  vagus  nerves,  on  account  of  the  great 
number  of  organs  to  which  these  nerves  are  distributed,  thus  induces  an  extreme 
disturbance  of  the  conditions  on  which  the  nutritive  equilibrimii  of  the  organism 
depends.  It  is  through  the  definite  loss  of  this  equilibrimn,  much  more  than 
through  any  localized  phenomenon  or  accident,  that  death  ensues  after  double 
vagotomy. 

Double  vagotomy. — Section  of  a  single  pnemnogastric  nerve  does  not  involve 
death.  The  two  nerves,  indeed,  easily  supplement  one  another,  doubtless  owing 
to  the  reciprocal  interpenetration  of  their  areas  of  distribution.  Double  section 
involves  death  in  the  dog  after  about  three  or  f ovir  days,  but  sometimes  the  delay 
is  longer.  It  varies  according  to  the  animal  ;  survival  is  especially  long  in  birds 
and  reptiles.  If,  between  the  two  sections,  a  period  sufficient  for  nerve  regenera- 
tion is  allowed  to  elapse,  the  animal  survives  (Philippeaux). 

g.     Spinal  Accessory. 

The  spinal  nerve,  the  accessory  nerve  of  WilHs  or  of  the  eleventh 
pair,  has  an  arrangement  and  performs  functions  which  are  somewhat 
special.  This  nerve  has  its  origins  in  the  medulla  oblongata,  and 
these  are  prolonged  from  those  of  the  pneumogastric  (in  the  collateral 
furrow),  and  it  has  also  origins  in  the  spinal  cord,  which  are  inde- 
pendent of  those  of  the  cervical  nerves.     From  this  point  of  view, 


200 


SYSTEMATIC  FUNCTIONS 


indeed,  it  is  rather  a  supplementary  spinal  nerve  than  an  accessory 
one,  because  it  discharges  an  important  function.  This  nerve  is  not 
found  in  fishes  and  the  amphibia.  It  first  shows  itself  in  reptiles  as 
a  branch  of  the  vagus. 

Boundaries. — Willis  regarded  these  spinal  cord  origins,  and  the  so- 
called  external  branch  which  continues  them,  as  being  the  whole  of 
the  spinal  accessory  nerve  ;  the  bulbar  roots  and  the  internal  branch 
which  originate  from  it  were,  on  the  contrary,  grouped  by  him  with 
the  trunk  of  the  pneumogastric.  Scarpa  reunited  the  two  branches 
(medullary  and  bulbar)  in  one  and  the  same  description,  because, 
united  to  each  other  in  the  posterior  lacerated  space,  they  there  form 
a  single  nerve  trunk ;  and  this  is  a  description  which  has  since  been 
given  of  them. 

Essentially  motor  function. — The  branches  of    origin  of  the  nerve 


--Ext.  laryng.  N. 
Slip,  laryng.  N. 


Becurrent. 


Fig.   90. — Terminal  branches  of  tlie  recnrrent. 

sometimes  bear,  one  or  the  other  exceptionally,  on  their  course,  a 
ganglion  of  which  it  is  difficult  to  say  whether  it  is  sensory  or  sym- 
pathetic. Experimentally,  sensory  elements  have  not  been  ascer- 
tained to  exist  in  this  nerve,  which  is  assumed  to  be  exclusively  motor. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS  201 

Isolated  destruction  by  tearing  out  of  the  nerve. — CI.  Bernard  has  devised  a 
method  which  allows,  iii  yoiuig  aiiiiiials,  the  isolated  destruction  of  the  root  of 
the  spinal  accessory,  by  means  of  a  trivial  operation  not  attended  with  great 
destruction,  and  wliich  assures  the  survival  of  the  subject.  It  consists  in  the 
tearing  out  of  the  nerve,  which  has  been  previously  laid  bare  at  its  exit  from  the 
posterior  lacerated  space. 

Carefully  adapted  progressive  traction  on  the  nerve  breaks  down  the  adhesions 
by  which  its  conjvuictival  sheet  is  attached  to  the  bony  canal,  and  the  forceps 
which  are  then  apjalied  to  it  brings  away  a  long  portion  which  represents  its 
roots  both  medullary  and  bulbar. 

It  is  possible,  indeed,  but  with  some  risk  to  the  success  of  the  experiment,  to 
tear  out  separately  either  the  medullary  roots  or  the  bulbar  roots  by  grasping 
separately  either  the  external  or  internal  branch  (CI.  Bernard). 


;  2  s         i        3        f        7 


Fig.   91. 


-The  principal  nerves  of  the  thorax  in  the  dog  (copied  from  Ellenberger  and 

Bamn). 


Phr,  phrenic  (in  red)  with  its  tlu'ee  roots,  v',  v",  v'",  arising  from  the  5th,  6th  and  7th  cervical. 

Va,  pneumogastric  with  its  cardiac,  CBSophageal  and  pulmonary  branches  and  the  recurrent 
nerve  R. 

ST,  sympathetic  thoracic  chain  with  its  ganglia  r,  r'  ;  s,  s',  intercostal  nerves  and  their  com- 
municating branches  proceeding  to  the  sympathetic  chain  ;  p,  first  thoracic  ganglion  and  its 
branches  of  imion  with  the  first  thoracic  nerves  ;  o,  its  branches  of  union  with  the  last  cervical 
X^airs  (vertebral  nerve)  ;  pc,  its  cardiac  branch  and  to  the  left  of  this  the  Ansa  Vieussenii  by  which 
the  thoracic  sympathetic  becomes  continuous  with  the  cervical  sympathetic  united  to  the  triuik 
of  the  pneumogastric  ;  Spl,  great  splanchnic  ;  u,  small  splanchnic  ;  1  to  13,  divided  ribs  accom- 
panied by  the  vessels  and  intercostal  nerves. 


A.  Internal  Brais[CH.— Vocal  function  of  the  spinal  accessory. — 
Destruction  of  the  spinal  accessory,  or  merely  of  its  internal  branch, 
if  effected  on  one  side  only,  produces  hoarseness  of  voice,  and  if  made 
on  both  sides,  completely  suppresses  the  emission  of  sounds  (CI.  Bernard). 

Hoarseness,  Aphonia. — Hoarseness  or  aphonia  is  the  consequence  of 
the  paralysis  of  the  chief  constrictor  muscles  of  the  glottis. 

If,  indeed,  in  an  animal  in  which  the  spinal  accessory  is  destroyed, 
the  thyro-hyoid  membrane  be  split  so  that  the  movements  of  the 
larynK  may  be  directly  observed,  it  is  seen  that  its  superior  orifice 
continues  dilated,  there  being  no  power  to  completely  close  it.  There 
are,  indeed,  slight  alternate  movements  of  dilatation  and  closure  ;  but 


202 


SYSTEMATIC  FUNCTIONS 


these  movements  are  those  which  are  always  observed  in  the  larynx, 
inasmuch  as  they  accompany  every  movement  of  inspiration  and 
expiration  of  air,  in  the  same  manner  as  the  movements  of  dilatation 
and  contraction  of  the  nostrils. 

Respiratory  function  of  the  vagus. — If,  after  having  (by  destruction 
of  the  spinal  accessory)  rendered  impossible  the  movements  of  the 
vocal  cords,  the  trunk  of  the  vagus  or,  rather,  the  recurrent  nerves, 
be  cut,  the  respiratory  movements  of  this  organ,  the  larynx,  will  also 
disappear.  The  orifice  of  the  larynx  not  only  no  longer  dilates,  but 
is  narrowed  and  immobilized,  and  if  the  experiment  is  made  on  a 
young  animal  (in  which  the  softer  membranes  yield  under  the  current 
of  inspired  air),  asphyxia  may  ensue. 


s^|.  H -  Dentale  Ligament.         '% 


^j--m 


Fig.  92. — Apparent  origins  of 
the  glosso-pharyngeal,  pneu- 
mogastric,  and  spinal  nerves. 


Fig.   93. — Real    origins    of    the    medullary 
portion  of  the  accessory. 


Antagonistic  nerves  and  muscles. — Thus  the  larynx  performs  two  orders  of 
movements,  which  correspond  to  two  distinct  functions  in  a  certain  degree 
antagonistic  ;  the  vocal  function  and  the  respiratory  function.  Certain  muscles, 
like  the  posterior  crico-arytsenoids,  whose  dilating  action  is  evident,  have  a  more 
exclusively  respiratory  function  ;  certain  others,  like  the  lateral  crico-arytaenoids, 
the  thyro-arytsenoids,  the  arytsenoids,  the  crico-thyroids,  which  approximate 
and  make  tense  the  inferior  vocal  cords,  possess  a  more  exclusively  vocal 
function. 

However,  the  vocal  and  respiratory  functions  make  use  now  of  the  one,  now 
of  the  other  of  these  muscles  for  the  execution  of  movements  wliich  only  differ 
in  their  result.  It  is  therefore  rather  the  nervous  elements  which  preside  over 
them  which  are  fixnctionally  distinct  and  in  a  certain  measure  antagonistic. 
Analdson,  Fr.  Hooper,  Livon  have  endeavoured  to  dissociate,  by  physiological 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS  203 

methods,  these  elements  scattered  in  the  trimlv  of  the  recurrent  nerves.  Accord- 
ing to  Livon,  it  is  jaossible,  by  varying  the  rhythm  of  tlie  stimulation  brought  to 
bear  on  these  latter  nerves,  to  obtain  distinct  effects  of  occlusion  or  of  dilatation 
of  the  glottis.  Dilatation  is,  however,  accompanied  with  movements  wliich  are 
sjnclironous  with  the  excitation  (animals  vinder  the  influence  of  chloroform, 
chloral  and  morphia,  and  an  ampulla  in  the  glottis  for  the  record  of  movements). 

Recurrent  Nerves. — The  nerve  fibres  which  come,  some  from  the 
origins  of  the  spinal  accessory  (for  the  vocal  cords),  the  others  from 
those  of  the  vagus  (respiratory  fibres),  after  mixing  momentarily  in 
the  trunk  of  the  vagus,  proceed  to  the  larynx,  chiefly  by  means  of 
the  recurrents,  with  the  exception  of  those  which  go  to  the  crico- 
thyroid, conveyed  thither  by  the  superior  laryngeal.  Hence,  if  either 
the  trunk  of  the  vagus  or  that  of  the  recurrent  be  cut,  both  sets  of 
fibres  are  divided  at  the  same  time  :  phonation  becomes  impossible 
and  the  respiration  is  embarrassed. 

Asphyxia. — In  very  young  animals,  section  of  the  recurrent  nerves  (and  con- 
seqviently  of  the  vagus)  may  be  followed  by  immediate  asphyxia  ;  while  in  older 
animals,  respiration  remains  possible,  although  it  may  be  slightly  embarrassed 
(Legallois).  This  is  owing  to  the  fact  that  in  the  first  the  delicacy  of  the  mem- 
branes of  the  larynx  (bomidaries  of  the  glottis)  causes  them  to  act  as  valves  when 
the  glottis  is  opened  at  each  inspiration,  and  in  this  way  they  produce  an  obstruc- 
tion to  the  entrance  of  air,  whereas  in  the  second  the  gi-eater  rigidity  of  these 
structures  causes  an  open  space  to  be  maintained  tlii'ough  wliich  the  air  can  pass  ; 
this  space  is  specially  defined  between  the  arytsenoid  cartilages  (inter cartila- 
ginous portion)  rather  than  between  the  vocal  cords  (interligamentous  portion 
of  the  glottis)  (Longet). 

Superior  laryngeal  nerve,  its  motor  function. — Section  of  the  superior  laryn- 
geal nerve  produces  merely  hoarseness  of  the  voice,  tlii'ough  paralysis  of  the 
crico-thyroid  and  want  of  tension  of  the  ^■ocal  cords. 

Stimulation  of  the  origins  ;  motor  effects. — AVhen  the  origins  of  the  spinal 
accessory  in  tlie  medulla  oblongata  are  irritated,  contraction  of  the  superior 
constrictor  muscle  of  the  pharynx  ensues  (Chauveau).  These  motor 
elements  are  supplied  to  the  pharyngeal  plexus  by  the  internal  branch  of 
the  spinal  accessory  after  it  has  entered  the  jugular  ganglion  of  the  vagus,  con- 
jointly with  other  branches  coming  from  tlie  vagus  itself  and  the  glosso- 
pharjTigeal. 

Cardio-inhibitory  effects. — The  internal  branch  of  the  spinal  accessory  origin- 
ally contained  inhibitory-  fibres  which  are  destined  for  the  cardiac  muscle.  If, 
indeed,  this  portion  of  the  spinal  accessory  is  cut  or  torn  out,  and  if  after  an 
interval  of  some  days  (so  that  the  cut  fibres  may  have  time  to  degenerate),  the 
vagus  be  stimulated,  this  excitation  no  longer  induces  slowing  or  stoppage  of  the 
heart  (Waller).  This  fact  has  been  disputed  by  several  observers  ;  there  may 
be  individual  variations  in  the  origin  of  tliese  nerves,  and  these  varieties  may  be 
present  in  the  two  nuclei. 

B.  External  Branch. — Its  function  in  exertion. — The  medullary 
portion  of  the  origins  of  the  spinal  accessory  forms  outside  the  skull, 
the  external  branch  of  this  nerve  which  suj)plies  the  sterno-mastoid 
and  trapezius  muscles.     It  forms,  for  these  muscles,  a  nerve   supply 


204 


SYSTEMATIC  FUNCTIONS 


superadded  to  that  wliicli  they  receive  from  the  neighbouring  cervical 
pairs,  and  which  also  appears  to  be  connected  with  phonation,  or 
rather  with  all  effort  wliich  necessitates  the  suspension  of  respiration. 
Section  of  the  spinal  accessory,  in  so  far  as  it  supplies  the  trapezius 
and  sterno-mastoid  muscles,  would  immobilize  the  thorax,  or  more  or 
less  suspend  expiration,  in  order  to  permit  it  to  adapt  the  column  of 
expired  air  to  the  modulations  of  the  voice. 

Section  of  the  external  branch  permits  the  persistence  of  the  voice, 
but  the  cries  are  shorter,  and  the  animal  soon  becomes  out  of  breath. 
From  this  point  of  view,  the  spinal  accessory  may  be  described  as 
the  nerve  of  effort  (CI.  Bernard). 

h.     Hypoglossal  Nerve 
The  hypoglossal,  or  nerve  of  the  twelfth  pair,  is  the  motor  nerve 


Gloss,  pharyn. 
Auric,  temp. 

Int.  max. 

Linjual. 
)~  St'il.  'jloss. 

Gl.  jiharyng. 
Siih.  mar.  gl. 
d  hijp.  (inastomo. 


[■  cen-ic.  — 


Com.  carut.  - 


Sup  laryngeal. 


Desc.  hyp  J.  br. 


Arc.  ana^'lomotic. 


Fig.   '.)4. — The  hypoglossal  wevxe  (after  Hii'schfeld). 

of  the  intrinsic  muscles  of  the  tongue  and  of  certain  muscles  of  the 
neck.  Being  such,  it  assists  in  the  movements  of  mastication  and  of 
deglutition. 

1.  Effects  of  section  ;  motor  paralysis. — Section  of  the  two  hypo- 
glossal nerves  in  the  dog  considerably  embarrasses  these  two  orders 
of  movement.  Nevertheless,  according  to  Philippeaux  and  Vulpian, 
it  does  not  render  them  absolutely  impossible,  as  Panizza  affirms. 
After  some  time,  the  animal,  by  divers  movements,  compensates  the 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    205 

inactivity  of  the  tongue.  This  latter,  although  having  lost  its 
intrinsic  movements,  is  not  on  that  account  rendered  completely 
immobile,  but  movements  are  communicated  to  it  by  the  muscles  of 
the  region  of  the  neck,  which  are  partially  innervated  as  much  by 
the  trigeminal  as  by  the  facial  or  the  cervical  nerves. 

The  hypoglossal  is  obviously  distributed,  not  merely  to  the  in- 
trinsic muscles  of  the  tongue,  but  to  a  considerable  number  of  those 
of  the  anterior  portion  of  the  neck.  But  as  regards  several  of  the 
latter,  this  is  a  borrowed  motricity,  inasmuch  as  the  nerve  of  the 
twelfth  pair  forms  two  important  anastomoses  with  the  cervical  plexus. 


Fig.   95. — Principal  nerves  of  the  head  in  the  dog  (after  EUenberger  and  Baum). 

a,  hypoglossal  nerve  ;  6,  its  descending  branch  ;  c,  inferior  maxillary  branch  of  the  trigeminal ; 
d,  lingual  nerve  ;  e,  chorda  tympani  ;  /,  deep  temporal  nerve  ;  g,  pterygoid  nerve  ;  h,  buccinator 
nerve  ;  i,  inferior  dental  nerve  ;  k,  branch  going  to  the  soft  palate  ;  I,  eliorda  tympani  before  its 
entrance  into  the  lingual  nerve  ;  m,  mylo-hj'oid  nerve  ;  n,  spheno-palatine  nerve  ;  o,  posterior 
palatine  nerve  ;  p,  anterior  palatine  nerve  ;  q,  sub-orbital  nerve  ;  r,  orbital  branch  of  the  superior 
maxillary  nerve  ;  s,  branch  of  the  oculo-motor  proceeding  to  the  inferior  obUque  muscle  ;  t, 
lachrymal  nerve  ;    u,  frontal  nerve  ;    v,  pathetic  nerve  ;    w,  external-oculo-motor  nerve. 

1,  common  carotid  artery  (in  black)  ;  2,  lingual  artery  ;  3,  internal  maxillary  artery  ;  4,  inferior 
pharyngeal  muscle  ;  6,  middle  pharyngeal ;  6,  thyro-hyoid  ;  7,  sterno-hyoid  ;  8,  hypoglossal  ; 
9,  genio-hyoid  ;  10,  genio -glossal  ;  11,  stylo -glossal  ;  1 2,  internal  pterygoid  ;  13,  locality  occupied 
by  the  sub-maxillary  gland  which  has  been  removed  ;  14,  atlas  ;  15,  tympanic  bulla  ;  16,  zygo- 
matic arch  ;   17,  inferior  rectus  muscle  of  the  eye  ;    18,  inferior  oblique. 


Superior  anastomoses. — The  first  occurs  at  the  level  of  the  first 
cervical  arch,  and  the  other,  much  lower  down,  is  effected  by  the 
descending  branch. 

Descending  branch.— The  descending  branch  of  the  hypoglossal 
descends  to  meet  the  branch  of  the  same  name  given  off  by  the  cervical 
plexus,  by  forming  a  loop,  from  which  are  detached  branches  for  the 
sub-hyoidean  muscles  (omo-hyoid,  sterno-hyoid,  sterno-thyroid).  Some 
observers,  with  Holl,  Beevor,  and  Horsley,  maintain  that  the  hypo- 
glossal is  distributed  only  to  the  intrinsic  muscles  of  the  tongue,  and 
that  the  branches  which  are  given  off  from  it  before  its  termination 


206 


SYSTEMATIC  FUNCTIONS 


are  furnished  by  these  two  anastomoses,  following  two  direct  or  more 
or  less  recurrent  tracts.  Wertheimer  has  observed  (in  the  dog)  that, 
after  section  and  degeneration  of  the  descending  branch  of  the  cervical 
plexus,  stimulation  of  the  hypoglossal  causes  contraction  of  the  sterno- 
hyoid and  thyro-hyoid  muscles  of  the  sub-hyoid  region. 

2.  Sensation  by  anastomosis. — The 
origins  of  the  hypoglossal  are  exclu- 
sively motor  (save  for  a  small  gang- 
lionic root,  which  is  in  no  respect 
constant,  and  which,  when  it  occurs, 
must  be  regarded  as  the  equivalent  of 
a  posterior  root).  After  its  exit  from 
the  anterior  condyloid  foramen,  this 
nerve  becomes  sensory  through  the 
anastomoses  which  come  to  it  either 
from  the  cervical  plexus  at  its  exit, 
or  from  the  lingual,  near  to  its  termina- 
tion. This  borrowed  sensibility  is 
furnished  to  it  by  anastomoses,  some 
direct,  others  recurrent,  especially  by 
the  anastomotic  loop  which  it  forms 
with  the  lingual. 

3.  Ganglionic  Anastomosis  ;  Vaso- 
constrictor Elements.  —  From  the 
superior  cervical  ganglion  the  hypo- 
glossal receives  an  anastomosis  by 
which  the  great  sympathetic  supplies 
the  vessels  of  the  tongue  with  a  large 
proportion  of  their  constrictor  ele- 
ments ;  the  others  come  to  it  by  the 
lingual,  together  with  the  dilators. 

If,  indeed,  in  an  animal  curarized  to  the  utmost  available  extent 
(in  order  to  avoid  intrinsic  contractions  of  the  tongue)  the  peripheral 
end  of  the  cut  hypoglossal  be  stimulated,  the  tongue  will  be  observed 
to  become  pale  through  constriction  of  its  vessels. 


Fig.  9G. — Diagram  showing  the 
relations  of  the  hypoglossal  nerve 
and  the  first  cervical  nerves  (after 
M.  Holl). 


The    cervical    roots    in    black 
hypoglossal  nerve  in  yellow. 


the 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS  207 


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biol...  1886  et  1887.— Schwalbe  .   .   .   Gangl.  cil.,  lena  Ges.  et  lena  Zeit.,  1878  et  1879. 

Trigeminal  Nerve. — Althaus,  Arch.  f.  klin.  Med.,  1870. — Bastlanelli,  R.  acad.  med. 
d.  Roma,  1895. — Bellingeri,  De  nervis  faciei.  1818.  Debierre  et  Lemaire,  Biol. 
1895. — Esciiricht,  Journ.  de  Magendie,  t.  IV. — Hirschberg,  Berlin.  Min.  Woch.,  1868. 
— Guttmann,  Berlin,  klin.  Woch.,  1868. — Krueckmann,  Sensib.  de  la  cornee,  Graefes 
Arch.,  vol.  XLI. — Laffont,  Trij.  fac.  symp.  chez  oiseau,  G.  R.  Ac.  sc,  1885,  t.  CI.  p. 
1286. — Long  et  Egger,  Paralysie  chez  I'homme,  Arch,  phys.,  1897,  p.  905. — Lugro, 
Rac.  desc.  Arch.  ital.  biol.,  1895. — Prevost,  Fonct.  gust,  du  lingual,  Arch.  Phys.,  1873. 
pp.  253  et  375.— QuENU,  Tic  doul.  Gaz.  des  hop.,  1894. 

Vaso-motor  Functions. — Dastre  et  Morat,  Biol.,  Rech.  sur  le  syst.  nerv.  %'aso-moteui*, 
Paris,  Masson. — Joi.yet  et  Laffont,  Biol.,  divers. — Laffont,  Biol.,  di\-ers. — Vulpi.\n, 
G.  R.  Ac   sc,  1885,  t.  CI,  p.  981. 

Trophic  Disturbances. — Antona,  II  Policlinico,  1894. — Doven,  Extirp.  gangl.  de 
Gasser,  Arch.  prov.  dechir.,  1895. — Krause,  24  congr.  chirurg.  allem.  1895. — Lfonard, 
These  Paris,  1894. — Marinesco  et  Sebieux,  Arch.  Phys.,  1893,  p.  455. — Ramier,  Plexus 
nerv.  de  la  cornee,  G.  R.  Ac.  sc,  1879,  t.  LXXXVIII,  p.  1087. — Schmidt,  Deutsch. 
Zeitsch.  f.  Nerv.  heilk.,  1895. 

Trophic  Disturbances  of  the  Eye. — Cl.  Bernard,  Z?^oL,  1874. — Bezold,  Deutsch.  Klin. 
1867. — Htppel,  Arch.  f.  Ophthalm.,  1867. — Magendie,  Journ.  de  Phys.,  i.  IV. — Mess- 
NER,  Zeitsch.  f.  vrat.  Med.,  1867. — Ranvier,  Anatomie  de  la  cornee. — Schiff,  Zeitsch. 
f.  vrat.  Med.,  1867. — Snellen,  Nederl.  Tij.  voor  Geneesk.,  1864  ;  De  vi  nervorum  in 
inflammationem,   1857. 

Intra-ocular  Tension. — Adamuk,  Wien.  Acad.,  1869. — Hippel  et  Grunhagen,  Arch, 
f.  Ophthalm.,  1868,  1869. — Hirschberg,  Gentralbl,  1875. 

Trophic  Disturbances;  the  Ear. — Gelle,  Gaz.  Med.,  1878. — Hagen,  Arch.  f.  exper. 
Path.,  1879. 

Vaso-motor  and  Adaptive  Function  ;  Vision,  Audition,  etc. — Doyon,  Vaso-mot.  retine. 
Arch.  Phys.,  1891. — Eckhard,  Gentralbl.  /.  Phys..  1892,  p.  129. — Jolyet  et  Laffont, 
G.  R.  Ac.  sc,  1879. — Laffont,  Biol,  1880. — Morat,  Ganglion  du  muscle  du  marteau. 


SENSATION  AND  MOTION— THEIR  RELATIONSHIPS    209 

Conjres  de  Linge,  1892. — Politzer,  Wurzh.  nnt.  Zeit.,  18(51  ;  Arch.  f.  Ohrenhpilk.,  1870. — 
Prevost,  Gangl.  spheno-palatin,  Arch.  Phys.,  1868,  pp.  7  et  207.— VoltoliniM^c/'-  /- 
■path.  .-1/!.1875.— VuLPTAN,  C.  R.  Ac.  sc,  1885,  pp.  851,  981,  1037,  1448. 

Facial. — Beaunis,  Biol,  1887,  p.  205. — Bkrard,  Journ.  des  connaiss.  med.,  1834-35. 
— Cl.  Bernard,  Gaz.  med.,  1857. — Bikeles,  Degen.  asc,  Wiener  med.  Presse,  1893. — 
Bochefontaine,  Procede  de  section  intracran.,  Biol.,  1879. — Brown-Sequard,  Gaz. 
med.  Biol..  1849  et  1869.— Chantre,  Arch.  Phys.,  1891,  p.  629.— Dexler,  Paralysie 
choz  lo  eheval,  dyspnee  par  occlusion  des  narines,  Wiener  med.  Presse,  1890. — Goede- 
CHEN.S,  X.  facialis  physiol.  et  path.,  1832. — Hallofeau,  Trajet  intracerebr.  ram.  super., 
Biol.,  1879,  p.  244.— Laffay,  Sect,  intracran..  Arch.  Phys.,  1897,  p.  498. — Ltii,  Paralysie 
.  .  .  niouvem.  des  paupieres,  Archivio  per  les  sc.  med.,  1884. — Vulpi.\n,  C.  R.  Ac.  sc, 
1878  ;    Biol.,   1861  et  1879. 

Nerve  of  Wrisberg  ;  Geniculate  Ganglion. — Birmingham,  Journ.  of  An.  und  Phys. 
1895.— Cannieu,  C.  R.  Ac.  sc,  1895,  t.  CXX,  p.  880,  et  Revue  de  laryngoL,  1894.— 
Chi.\ritgi,  Monit.  zool.  ital.,  1896. — Froriep,  Corde  tymp.,  Anat.  Anz.,  1887. — Penzo, 
Anat.  An-.,  1895.— Vulpian,  C.  R.  Ac.  .^c,  1885,  t.  CI,  p.  1037  ;  1886,  t.  CIII,  p.  071. 
Ciiorda  Tympani  ;  Vaso-motor  Functions  ;  Gustatory  Functions. — Blau,  Berlin,  klin. 
Woch.,  1879. ^Carl,  Fonct.  gustat..  Arch.  f.  Ohrenheilk.,  1875. — Lussana,  Sui  nervi 
del  gusto,  Gaz.  med.  ital.,  1871. — Stich,  Ann.  d.  Charite  Frank,  z.  Berlin,  1857. — Vul- 
pian, C.  R.  Ac  sc,  1872,  et  Biol. 

Glosso-pharyngeal. — Biffi  et  Morganti,  Ann.  univ.  di  med.,  1846. — Cadman,  Glosso- 
phar.  vaffue  et  spinal,  Journ.  of  Phys.,  1901,  1,  p.  42. — Isergin,  Arch.  f.  An.  und  Phys., 
1894,  p.  441. — Katzenstein,  Arch.  f.  An.  und  Phys.,  1894,  p.  192. — Kronecker  et 
Met.tzer,  Arch.  f.  An.  und  Phys.,  1883,  svippl.  p.  328. — Lussana,  Xerfs  du  gout.  Arch. 
Phys.,  1871,  2,  pp.  150.  334,  522. — Marinescu,  Innerv.  driis.  zungenbasis,  .47-c/i. /.  An. 
und  Phi/s.,  1891,  p.  357. — Muchin,  Centralbl.  Nerv.  heilk.,  1893.— Pope,  Brit,  med., 
1889,  I.— Sandmeyer,  Arch.  f.  An.  und  Phys.,  1895,  p.  269. — Vtntschgau  et  HiiNiG- 
scHMiLD,  Arch.  V.  Pfiiig-,  1877,  t.  XIV,  p.  443.— Vulpian,  C.  R.  Ac  sc,  1880,  t.  XCT, 
p.  1032. 

Pneumo-gastric. — Arthaud  et  Butte,  Du  nerf  pneuniogast.  physiol.  norm,  et  path., 
Paris,  1892. — Van  Kempen,  These  Louvain,  1842. 

Respiration  ;  Lung.— D' Arsonval,  These  Paris,  1877. — Beer,  Arch.  f.  An.  und  Phys., 
1892.  suppL,  p.  101. — P.  Bert,  LeQons  sur  la  respiration. — Boris  Bjruckoff,  Arch.  f. 
An.  und  Phys.,  1899,  p.  525.— Brown-Sequard,  Arch,  de  Phys.,  1882  a  1891.— G. 
Brown,  Journ.  of  Phys.,  t.  VI,  1885. — Consiglio,  Arch.  ital.  de  bioL,  1892,  t.  XVII, 
p.  49.— Cou\TiEUR,  Circul.  pulmon.  gren.,  C.  R.  Ac  sc,  1889,  t.  CIX,  p.  823.— Dovon, 
Arch.  Phys.,  1893,  p.  93.  — T.  Gard,  Arch.  f.  An.  und  Phys.,  1881.— Grehant,  Ech. 
resp.,  Biol.,  1882. — Fredericq,  Traite  de  physiologic.  Bull.  Ac.  roy.  Belg.,  1879. — Kohts 
et  TiEGEL,  Arch.  v.  PfHiq.,  1876,  t.  XIII,  p.  84.— Hering  et  Breuer,  1868.— Rosenthal, 
Arch.  f.  An.  und  Phijs.,\m2  a  1881  :  C.  R.  Ac.  sc,  1861.— Schiff,  Arch.  v.  Pfliig.,  1871, 
t.  IV,  p.  226  ;  C.  ii.  Ac.  sc,  1861  ;  Lehrbuch.  Musk,  and  X^erv.  physiol.,  1858-59. — 
Spallita,  Arch.  ital.  de  hiol.,  1891,  t.  XV,  p.  376. — Stefani  et  Sighicelli,  Arch.  ital. 
de  hiol.,  1889.  t.  XI,  p.  143.— Treves,  Arch.  ital.  de  hiol.,  1897,  t.  XXVII,  p.  169. 

Laryngeal  Nerves. — Bedor,  These  Paris  (ictus  larynge),  1895. — Boddaert,  Arch. 
Phys.,  1862,  p.  443. — C.\oney,  Abduct,  et  adduct.,  Deutsch.  Zeitschr.  f.  Nervenheilk., 
1895. — Donaldson,  Americ  Journ.  of  the  med.  sc,  1886. — Exner,  Arch.  f.  ges.  Phys., 
1893  ;  Arch.  f.  An.  und  Phys.,  1891. — Fr.  Franck,  Journ.  de  Vanat.,  1877,  p.  500  ; 
Anast.  de  Galien,  C.  R.  Ac.  sc,  1879. — Katzenstein,  Arch.  f.  An.  und  Phys.,  1894  a 
1899. — Krishaber,  Biol.,  1880. — Hedon,  Elem.  vaso-dilat.  et  secret.,  C.  R.  Ac.  sc, 
1896,  t.  CXXIII,  p.  207.— Howell  et  Hubeh,  Journ.  of  Phys.,  1891,  p.  5.— Jean,  Soc. 
anat.,  170. — Legallois,  djuvres,  1830. — Livon,  Act.  des  recurrents,  Biol.,  1890  ;  Arch. 
Phys.,  1890,  p.  587,  et  1891.— Loewy,  Arch.  f.  d.  ges.  Phys..  1893.— Masini,  Acad,  de 
Genes,  1893.— H.  Munk,  Arch.  f.  An.  und  Phys.,  1891,  pp.  175  et  542,  et  1894,  p.  192. — 
Xeumann,  Centralbl.  f.  med.  Wiss.,  1893. — Onodi,  Muscle  crico-thyro'idien.  Revue  de 
laryng..  otol  et  rhinol,  1893.— Pineles,  Cen^roi6Z.  f.Phys.,IV,  Xo.  24,  p.  741.— Rauge, 
Arch,  de  Phys.,  1892.— Todd  et  Gardner,  Arch.  gen.  med.,  1853.— Zuntz,  Arch.  f.  An. 
und  Phys.,  1892,  p.  103. 

Heart.— Arloing,  Tetanos  du  myocarde.  Arch.  Phys.,  1893,  p.  103,  et  1894,  pp.  85  et 
163.— Arloing  et  Tripier,  Arch.  Phys.,  1871,  72,  73.— Francois  France,  C.  R.  Ac  sc, 
1880;  Action  antitonique,  ^rc/i.  P/(.2/s.,  1891. — A.  Gamgee,  Excit.  alternat.  .  .  .  Journ. 
of  Phys.,  1879-80,  vol.  I,  p.  39. — Gaskell.  Chansem.  electr.  .  .  .,  Journ.  of  Phys., 
1886,  p.  451.— GuRBSKi,  Sensib.  du  cceur.  Arch.  v.  Pflug.,  1872,  t.  V,  p.  289.— Labobde, 
Arch.  Phys.,  1888.— Laulanie,  Effets  second.,  C.  R.  Ac.  sc,  1889,  t.  CIX, pp.  377et407. 
— Legros  et  Onimus,  C.  R.  Ac  sc,  1872,  t.  LXXV,  p.  1192.— W.  Mills,  Journ.  of  Phys.. 
1884,  t.  V,  p.  359.— Munzel,  Arch.  f.  An.  und  Phys.,  1887.  p.  120.— Onimus,  C.  R.  Ac. 
sc,  1870,  t.  LXXXIII,  p.  988.— H.  Sewald  et  F.  Donaldson,  Journ.  of  Phys.,  1880-82, 
vol.  Ill,  p.  357. — Stefant,  Act.  protect..  Arch.  ital.  de  hiol,  i.  XXIII,  p.  175. — Stewart, 
Temperat.,  Journ.  of  Phys.,  1892,  p.  59.— Tarchanoff,  Arch.  Phys.,  1875,  p.  498.^ 

V.  P 


210  SYSTEMATIC  FUNCTIONS 

Tarchanoff  et  Puelma,  Excit.  alternat.  des  deux  vagues.  Arch.  Phys.,  1875,  p.  757. — 
Zandek,  Oiseaux  .   .   .,  Arch.  v.  Pfliig.,   1879,  t,  XIX,  p.  2G3. 

Pharynx,  CEsophagus,  Stomach  and  Intestine. — Cl.  Bernard,  Secretion  .  .  .,  Bvll. 
Acad,  de  med.,  1852. — V.  Braam  Houckgekst,  Mouvements  .  .  .,  Pfliig.  Arch.,  Bd.  VT, 
p.  266,  et  Bd.  VIII,  p.  163. — Chauveau,  N.  pneiunogast.  ag.  excit.  contr.  oesophagi- 
ennes,  Journ.  Phys.  de  Vhomme  et  des  animaux,  t.  VI,  1862  ;  Excitation  des  nerfs  cra- 
niens,  Ihid. — Ehrmann,  Intestin.  .  .  .,  Wiener  med.  Jahrb.,  1885. — Espe/.el,  Innerv. 
cesoph.,  Journ.  de  Phys.  et  pathol.  1901. — Longet,  Mecan.  occlusion  de  la  glotte,  deglu- 
tition. Arch.  gen.  med.,  1841. — Morat,  Lyon  med.,  1882. 

Liver. — Cl.  Bernard,  Lemons  sur  la  physiol.  experim.,  1854,  t.  I,  p.  336. — Doyon, 
Voies  biliaires,  these  Fac.  sc.  Paris. — Filehne,  Centralbl.  f.  Med.,  1878. — Heidenhain 
Stud.  Phys.  Inst.  z.  Brcslau,  Heft  2  vxnd  4. — Laffont,  C.  R.  Ac.  sc,  1880  ;  Journ.  anat. 
et  Phys.,'  1880. 

Kidney,  Bladder. — Arthaxjd  et  Butte. — Masius,  Bull.  Ac.  ray.  Belg.,  1888. — Oehl, 
<7.  R.  Ac.  sc,  1865. — G.  Ske  et  Gley,  Azoturie  .  .  .,  Biol.,  1888. — Vulpian,  Vaso- 
moteurs,  t.  I. 

Spleen. — Bochefontaine,  Arch.  Phys.,  1873. — Oehl,  Schmidt's  Jahrb.,  1869. — 
Tarchanoff,  Arch.  Pfliig.,  1873. 

Spinal  Accessory  Nerve. — Th.  Bischoff,  Nervi  accessor.  Will.  an.  et  phys.,  Heidel- 
berg, 1832. — Btscons  et  Mouret,  Biol.,  1894. — Cl.  Bernard,  Arch.  gen.  m,ed.,  1844  ; 
Lemons  sur  le  syst.  nerveux. — Longet,  Gaz.  med.,  1841. — Mirto  et  Pusateri,  Riv.  di 
pathol.  nerv.  element.,  1896. — Scarpa,  De  gangliis  nervorum  .  .  .,  H.  Weber,  Milano, 
1831. — W.  Schlottmann,  Detit.  Zeitsch.  f.  N ervenheilh . ,  1894. 

Hypoglossal  Nerve. — Dieloff,  Clin,  neuro-psych. ,  1896. — Duval,  Noy.  d'origine 
differents  pour  la  parole  et  pour  la  deglutition,  Biol.,  1879,  p.  239. — Fere,  Spasme  des 
muscles  .  .  .,  Biol.,  1827,  p.  239. — Laffont,  Annee  med.,  1883. — Wertheimer,  Anas- 
tom.  br.  descend.,  Biol.,  1884,  p.  589. 


CHAPTER    II 


PRIMARY   SYSTEMATIZATIONS 

Sensation  and  motion  are  present  in  us  in  forms  which  are  extremely 
finely  graduated.  Those  of  these  forms  which  correspond  to  the  idea 
ordinarily  held  of  sensation  (conscious  sensation)  and  of  movement 
(voluntary  movement)  are  the  most  elaborated,  and  also  the  most 
complex.  They  are  founded  on  more  elementary  associations  both  of 
sensibility  and  of  movement  than  we  can  recognize.  We  will  examine 
three  of  them  :  in  the  first  place,  reflex  action  is  that  which  demon- 
strates to  us  in  its  greatest  simplicity  the  transformation  of  a  sensory 
into  a  motor  excitation,  movement  being  the  end  which  is  aimed  at. 
Hence,it  is,  further,  a  phenomenon  which  often  intervenes  (perhaps  even 
habitually  to  a  certain  degree)  in  the  reflex  act  which  it  complicates 
and  to  which  it  gives  a  novel  aspect  and  physiognomy.  In  the  second 
place,  inhibition  or  arrest,  a  phenomenon  in  virtue  of  which  the 
sensory  excitation  does  not  exert  its  immediate  effect,  but,  on  the 
contrary,  suspends,  post- 
pones the  motor  effect, 
and  in  this  way  increases 
its  variety.  Lastly,  it  is 
the  inverse  bond  exist- 
ing between  movement 
and  sensation  which  per- 
mits them  to  maintain 
themselves  mutually  in 
the  organism,  in  an 
automatic  fashion,  thus 
preserving  the  impulse 
in  its  interior,  indeed, 
in  the  interior  of  the 
nervous  system,  by  a 
genuine  circulation  com- 
parable to  that  of  matter 
and  of  energy. 

Origin  of  the  nervous  system. — The  nervous  system  is  rendered  necessary  by 
the  complications  of  the  oi'ganization  of  animals  arranged  in  an  ascending  series. 
In  proportion  as  the  functions  become  more  numerous  through  differentiation 

211  p* 


Lat.  rentri. 


Zrd  renin. 


Aq.  Sylvius  .. 


ith  rentri. 


Epen.  can 


Front  lirain 

Uwmispheres). 


Inlermed.  brain 

(optic  thalamus). 


Mithlle  brain 

{Cerebral  ped.} 


Post  brain 

(Cerebellum). 


nacic  brain  (Bulb). 


Spinal  cord. 


Fig.   97. — The    cerebral    vesicles    in    the    embryo 
(diagram  copied  from  Gegenbam'). 


212 


SYSTEMATIC  FUNCTIONS 


by  the  division  of  labour,  a  special  tissue  is  develoi)ed,  whose  duty  it  is  to  har- 
monize these  different  portions  and  to  maintain  their  organization. 

In  the  freshwater  hydra,  the  body  wall,  proceeding  from  the  exterior  to  the 
interior,  is  divided  into  two  epitlielial  layers,  one  external  and  the  other  internal. 
Between  the  two  is  a  sort  of  intermediate  layer  of  contractile  natvire.  This 
interjDosed  layer  is  not  formed  of  independent  elements,  but  the  fibres,  appar- 
ently muscular,  which  compose  it  are  attached  by  a  bridge  of  continuous  sub- 
stance to  the  epithelial  elements  of  the  superficies.  The  excitations  received 
by  the  external  surface  of  these  latter  are  thus  transmitted  by  continuity  of 

substance  to  their  deep 
portion,  which  is  mus- 
cular, or  at  least  con- 
tractile. Those  tracts, 
which  connect  two  func- 
tionally differentiated 
portions  of  a  similar 
element,  may  be  looked 
upon  as  the  ]3reliminary 
sketch  of  a  nervous 
tissue. 

In  other  animals 
whose  organization  is 
still  very  rudimentary, 
we  find  this  tissue  iso- 
lated fron:i  other  tissues, 
forming  a  rudimentary 
system.  Such  is  the 
nervous  system  of  an 
ascidian,  formed  of  a 
ganglion  which  is  con- 
nected by  structures  or 
by  nerves  properly  so 
called  to  organs,  some 
recejotive  of  stimulation, 
others  which  perform 
fvinctions.  This  little 
elementary  system  is  a 
reflex  arc  similar  to 
innumerable  others 
found  in  superior  ani- 
mals, but  in  them  co- 
ordinated amongst 
themselves  and  organized  into  a  series  of  complicated  systems  of  which  they 
form  the  constituent  elements. 

Its  development. — The  nervous  system  in  the  vertebrata  is  obvious  from  the 
very  earliest  days  of  development.  It  takes  origin  in  the  ectoderm.  In  the  first 
instance  it  presents  itself  under  the  form  of  a  thickened  band,  neural  plate  or 
neural  furroiv.  This  furrow  is  transformed  into  a  groove  {medullary  or  neural 
groove)  which  is  orientated  in  the  direction  of  the  long  axis  of  the  body.  Its 
borders  project  upwards,  unite,  and  thus  form  the  medullary  or  neural  canal. 
This  canal  becomes  separated  from  the  rest  of  the  ectoderm,  which  closes  below 
it.  It  already  represents  the  spinal  cord  with  its  ependymal  canal.  At  its 
anterior  extremity  this  canal  forms  three  dilatations,  which  are  the  cerebral 
vesicles  [anterior,  middle  and  posterior),  which  will  give  rise  to  the  encei^halon. 


^/e// 


Dors 


h\iman 


Fortion 
Fig.  98. — Section     of     the     encephalon     in     a 
embryo  about  a  month  old  (after  W.  His). 

The  figures  1,  2,  3  correspond  to  the  primary  vesicles  : 
1,  rhomb-encephalon  (rhomboid  brain)  ;  2,  mesencephalon 
(middle  brain)  ;   3,  prosencephalon  (anterior  or  front  brain). 

The  figures  I,  II,  III,  IV,  V,  VI  correspond  to  the  secondary 
vesicles  :  I,  myelencephalon  (back-brain)  :  II,  metenceph- 
alon  (posterior  brain)  ;  III,  isthmencephalon  (isthmus  of  the 
rhombencephalon)  ;  IV,  mesencephalon  (middle  brain) ; 
V,  diencephalon  (intermediate  brain)  :  VI,  telencephalon 
(terminal  brain). 


PRIMARY    SYSTEMATIZATIONS 


213 


Geniculate  bodies 


Rhinencephalon 
Optic  depression 


Chiasm 

( Infundibu' 

lum) 


Fig. 


Cerebellar 

hemispheres. 


human 


The  division  of  the  anterior  and  posterior  vesicles,  each  of  wliich  forms  two  new 
vesicles,  increases  to  five  the  niimber  of  secondary  vesicles,  and  thus  produces 
an  anterior  brain,  an  intermediate  brain,  a  middle  brain,  a  posterior  brain,  and 
an  after  brain.  The  primitive  middle  vesicle  becomes  the  middle  brain.  The 
anterior  brain  (the  most  anterior  of  the  secondary  vesicles)  becomes  very  con- 
siderably developed  in  man.  It  divides  on  the  median  line  and  gives  origin  to 
the  two  hemispheres  separated  by  the  interhemispherical  fissure.  All  these 
vesicles  and  the  cavities  which  they  contain  assiime  very  different  configvirations, 
and  give  rise  to  new  formations. 

The  portion  of  the  primitive  canal  which  corresponds  to  the  middle  brain 
becomes  relatively  con- 
tracted, and  forms  the 
aqueduct  of  Sylvius,  which 
commimicates  posteriorly 
with  an  enlarged  portion  of 
the  after  brain,  the  fourth 
ventricle  itself  being  con- 
tinuous with  the  ependymal 
canal  of  the  spinal  cord. 
The  aqueduct  of  Sylvius  is 
continuous  in  front  with  the 
third  ventrical  (of  the  inter- 
mediary brain),  and  in  this 
way  communicates  with  the 
lateral  ventricle  hollowed 
out  in  each  hemisphere. 
According  to  the  nomen- 
clature of  His,  the  posterior 
primitive  vesicle  includes 
yet  another  division,  the  heinispheres. 
isthmus  of  the  rhombence- 
phalon, which  increases  the  number  of  secondary  divisions  to  six. 

The  wall  of  the  neixral  canal  is  at  first  formed  of  a  single  row  of  cells  which 
constitute  its  thickness.  Yet,  alongside  of  these  epithelial  cells,  which  will  remain 
in  position  and  will  become  the  elements  of  the  ependyma,  others  are  also  pre- 
sent, wliich  are  in  process  of  caryocinetic  division,  to  wliich  His,  who  observed 
them,  has  given  the  name  of  germinative  cells.  At  a  given  moment,  which  varies 
for  each  of  them,  these  latter  cease  to  multiply  and  become  neuroblasts,  that  is 
to  say,  cellular  elements  gi\'ing  rise  to  neurons.  Through  the  development  of 
their  prolongations  beyond  the  medullary  cylinder,  certain  of  them  proceed  to 
join  the  muscles.  By  tjirusting  out  these  prolongations  towards  the  interior 
both  of  the  brain  and  the  cord,  the  elements  of  which  they  are  formed  enter  into 
relation  the  one  with  the  other.  It  remains  for  the  connexion  of  the  central 
parts  with  the  skin  and  the  organs  of  sense  to  be  established.  This  is  effected 
by  elements  which  have  remained  outside  these  masses  at  the  time  of  their 
formation. 

Diiring  the  period  in  which  the  neural  fvirrow  is  hollowed  out,  its  borders  pre- 
sent a  crest  {neural  or  ganglionic  crest)  ;  it  is  from  tliis  double  crest,  wliich  is  first 
of  all  luiited  and  then  dissociated,  that  the  spinal  ganglia  take  their  origin.  The 
cells  of  these  latter  join  the  skin  on  the  one  hand,  and  on  the  other  the  spinal 
cord,  and  in  this  way  the  cycle  of  excitation  is  completed.  In  the  invertebrata 
(and  also  in  the  vertebrata  as  regards  the  organs  of  sense  other  than  touch)  these 
cells  remain  scattered  at  the  periphery  in  contact  with  the  ectoderm  and  are 
joined  to  the  grey  axis  by  their  axons. 


99. — Section    of    the    encephalon    in    a 
embryo  of  five  weeks  (after  W.  His). 

More  advanced  development  of  the  different  formations 
arising    from    the    cerebral     vesicles,    and     especially    the 


214  SYSTEMATIC  FUNCTIONS 

A.  COMMUNICATION  OF  STIMULATION  ;  REFLEX  ACT 
The  reflex  act  is  of  all  systematic  nervous  actions  the  simplest. 
Theoretically,  it  requires  the  participation  of  two  nerve  elements,  one 
of  which  transmits  to  the  other  the  impulse  which  it  has  itself  received. 
The  existence  of  this  simple  connexion  between  certain  neurons  is 
easily  demonstrated,  especially  between  the  elements  of  the  posterior 
roots  and  those  of  the  anterior  roots  of  the  spinal  cord. 

If,  for  example,  in  a  frog,  a  small  segment  of  the  spinal  cord  cor- 
responding to  a  nerve  pair  (metameric  segment)  is  isolated  between 
two  sections,  and  if  then  the  sensory  nerve  be  stimulated  either 
directly  or  by  irritation  of  the  skin,  the  muscles  to  which  the  motor 
nerve  is  distributed  will  respond  by  a  contraction.  The  impulse 
starting  in  the  skin  is,  as  is  said,  reflected  by  the  spinal  cord  in  such 
a  way  as  to  return  near  to  its  point  of  departure. 

Historical. — Long  ago  it  liad  been  remarked  that  certain  movements  which 
were  altogether  involuntary  ensued  as  a  response  to  sensitive  or  sensorial  excita- 
tions. The  phenomenon  had  been  observed  and  recorded  by  Montaigne  and 
Descartes  ;  ft  ajjpears  that  Astruc  had  already  described  it  as  "  reflex  "  (1743)  ; 
but,  according  to  Longet,  it  is  to  Prochaska  (1784)  that  the  first  experimental 
data  concerning  the  question  are  due.  He  was  the  first  to  observe  the  move- 
ments of  response  of  the  decapitated  frog  when  its  skin  is  irritated  ;  he  attri- 
buted these  movements  to  a  phenomenon  which  was  centred  in  the  spinal  cord, 
and  which  he  designated  by  the  name  which  it  has  since  preserved  :  "  itnpres- 
sionum  sensoriariutn  in  motorias  reflexio  "  ;  he  saw  quite  clearly  the  simjDle  rela- 
tion which  exists  in  this  case  between  sensation  and  movement.  He  compared 
to  these  facts  the  involuntary  acts  which  are  obser^^ed  in  man,  such  as  winking 
of  the  eyelids,  sneezing,  coughing,  vomiting,  following  a  sensorial  or  sensory 
impression  which  is  rather  active  and  unexpected  or  extra-functional,  and  also 
the  movements  of  the  limbs  induced  by  irritations  of  the  skin  during  sleep  or 
in  apoplectic  patients,  as  being  movements,  so  to  sjDeak,  indeiaendent  of  con- 
sciousness and  of  the  will. 

Legallois  reproduced  these  facts  and  these  observations  without  recognizing 
their  nature.  His  exjoeriments  confirm  the  reflex  or  intrinsic  power  of  the  spinal 
cord  which  he  observed  in  mammals  after  section  of  the  bulb  by  effecting  pul- 
monary insufflation.  Lallemand  observed  facts  of  this  kind  in  anencephala. 
Calmeil  equally  insisted  on  the  function  of  motor  co-ordination  of  the  spinal 
cord  as  being  independent  of  that  of  the  encephalon.  J.  Miiller  and  Marshall- 
Hall  extended  these  data  and  applied  them  to  the  explanation  of  a  large  number 
of  pathological  phenomena. 

Extension  of  the  phenomenon. — Inasmuch  as  the  muscular  movement  is  the 
most  visible  of  any  in  the  organism,  it  was  only  natural  that  it  shovild  at  first 
serve  as  the  chief  characteristic  of  the  reflex  phenomenon.  But  when  CI.  Ber- 
nard and  Ludwig  had  extended  the  action  of  the  nervous  system  to  the  vessels 
and  glands,  the  area  of  reflexes  took  a  new  extension  and  became  in  a  way  gener- 
alized. As,  on  the  other  hand,  the  vaso-motor  and  secretory  nerve  influence 
is  always  involuntary,  the  reflex  act,  from  being  in  some  degree  an  exceptional 
phenomenon  as  it  at  first  appeared,  became  the  primary  and  essential  form  of 
the  function  of  innervation.  Voluntary  movement  is  nothing  more  than  the 
elaborated  form  of  reflex  action  ;  muscular  movement  is  itself  merely  a  differ- 
entiated form  of  organic  movement  usually  hidden  and  invisible. 


PRIMARY    SYSTEMATIZATIONS 


215 


1.  Localized  reflex  actions. — Masiiis  and  Vanlair,  by  the  method 
of  systematic  section  of  the  myelaxis,  have  proved  that  each  seginent 
of  the  spinal  cord,  corresponding  to  a  nerve  pair,  can  act  as  a  point  of 
reflection  of  the  impressions  from  the  sensory  root  to  the  corresponding 
motor  root.  Each  of  these  segments  is  limited  by  two  planes,  the 
posterior  passing  immediately  behind  the  insertion  of  the  correspond- 
ing roots,  the  anterior  immediately  behind  the  roots  of  the  pair 
situated  in  front.  It  is  in  every  case,  with  this  limitation  as  regards 
the  segments,  that  reflection  is  most  favourably  observed.  The 
lumbar  enlargement  of  the  spinal  cord  is  very  well  adapted  for  this 
investigation.  The  segment  corresponding  to  the  tenth  pair  of  spinal 
roots  can  be  perfectly  isolated  from  the  others,  the  segment  of  the 
seventh  pair  equally  so  ;  it  is  more  difficult  to  dissociate  the  eighth 
and  the  ninth  segment,  inasmuch  as  the  sensory  areas  of  these  two 
nerve  pairs  are  less  distinct. 


Fig.    100. — Cutaneous  areas  of  the  Vllth,  Vllltli,  IXtli  and  Xth  nerves  of  the  frog. 
On  the  light  front  view  and  on  the  left  back  view  of  the  animal.    D,  right  limb  ;  G,  left  limb. 
These  areas  are  determined  by  the  reflex  responses  to  the  stimuli  brought  to  bear  upon  them. 

These  authors  have,^indeed,  commenced  by  determining  the  cutaneous 
territories  corresponding  to  the  sensory  roots  of  each  nerve  pair  by 
separately  cutting  these  roots,  in  order  to  ascertain  the  corresponding 
area  of  anaesthesia.  Then  they  experimented  on  these  areas,  thus 
delimited,  in  order  to  produce  excitation.  The  reflex  movements  are 
more  marked  when  the  sensory  receptive  apparatus,  which  is  adapted 
to  the  functional  stimulation,  is  acted  upon  than  when  the  stimulus 
is   brought  to  bear  upon  the  sensory  nerve  itself. 

Anatomical  data.  Connexions  between  elements. — Anatomy,  thanks  to  the 
employment  of  new  methods  (metliod  of  Golgi),  has  demonstrated  the  existence 
of   these    connexions.     In  a  section  of  the  spinal  cord,  certain  collaterals  of  the 


216 


SYSTEMATIC  FUNCTIONS 


posterior  roots,  which  proceed  in  the  grey  matter  in  order  to  come  in  contact 
with  the  dendrites  of  the  anterior  roots,  may  be  followed  (Cajal).  Thus  the 
reflex  ai'c  is  formed  by  a  system  of  at  least  two  nerve  elements,  connected 
consecutively,  but  this  association  is  not  so  simple  as  is  commonly  suj^posed. 
By  observing,  indeed,  in  a  spinal  segment  artificially  isolated  as  above,  that  the 
sensory  root  corresponds  to  a  motor  root,  it  might  be  supposed  that  each  fibre 
of  the  one  corresponds  in  the  same  way  to  a  fibre  of  the  other  ;  but  this  is  not 
the  case.  The  field  of  distribution  of  a  sensory  neiu"on  corresjaonds  to  several 
motor  neurons  (certain  of  them,  indeed  extend  to  a  great  length  of  the  spinal 
cord).  Conversely,  the  initial  arborizations  of  the  motor  neurons,  although 
occuj^ying  a  much  less  extended  area,  enter  into  relationship:)  with  several,  sensory 
neurons. 

There  is  reciprocal,  although  unequal,  overlap^^ing  of  the  areas  by  which  these 
contacts  are  effected.  The  impulse  conveyed  by  a  single  sensory  element  is  trans- 
mitted,  in  a  certain  order,  to  several  motor  elements,  and  the  impulse,  sitnultaneously 


^'eiisory  nerve 


•■'piirii  gmgl. 


Fig.    101. — Elementary  reflex  arc. 

Course  of  a  sensory  iinjjression  and   a  motor  impulse  passing  througli  the  same  level  of  the 
spinal  cord. 


conveyed  by  several  sensory  elements,  may  converge  on  a  single  motor  element.  On 
account  of  similar  connexions,  the  imjjulse  undergoes  a  special  arrangement  in 
the  grey  matter  which  gives  to  it  an  entirely  new  form  of  aggregation.  It  is,  as 
we  say,  transformed. 

Elements  of  association. — Not  only  have  the  two  neurons  known  as  sensory 
and  motor  these  complicated  connexions,  but  it  is  not  proved,  even  for  the  per- 
formance of  the  most  simple  reflexes,  that  these  conditions  suffice,  and  it  is  neces- 
sary to  take  into  account  elements  superadded  to  the  preceding.  Intermixed 
with  the  terminal  and  initial  arborizations  of  the  neurons  thus  joined  together 
are  ramifications  of  short  cells  discovered  by  Golgi ;  these  elements  are  neurons 
running  a  short  cotirse,  which  would  seem  to  serve  as  a  means  of  association 
between  the  preceding.     Hence  an  impulse,  in  order  to  proceed  from  a  sensory 


PRIMARY    SYSTEMATIZATIONS  217 

to  a  motor  nerve,  follows  routes,  some  of  which  are  direct,  others  roundabout, 
each  of  which  in  its  own  way  contributes  to  give  to  the  process  of  stimulation  a 
necessarily  comjilex  asjiect. 

Forms  of  reflex  movement  varied  according  to  the  point  of  departure,  or  the 
intensity  of  stimulation. — It  has  been  shown  experimentally  that  irritation  of 
different  areas  of  the  skin  may  produce  varied  reflex  movements  of  the  different 
articulations  (Sanders-Hezn)  ;  thus  the  difference  in  intensity  of  the  stimulation 
will  give  rise,  when  weak,  to  a  movement  of  flexion  ;  when  strong,  to  a  movement 
of  extension  of  the  hind  limb  (Vulpian). 

2.  Typical  form. — Etymologically,  the  word  reflex  signifies  "  return 
of  the  impulse  towards  its  point  of  departure  by  passing  through  that 
which  is  known  as  a  centre."  The  ganglia  of  the  great  sympathetic, 
the  grey  matter  of  the  spinal  cord,  furnish  simple  examples  of  this 
phenomenon.  But,  according  as  the  impulse  penetrates  more  or  less 
deeply  into  the  central  masses  of  the  nervous  system,  according  as  it 
reaches  the  medulla  oblongata,  the  basal  ganglia,  or  even  the  cerebral 
cortex,  the  reflex  act  becomes  continually  more  complicated,  without 
ceasing  to  be  finidamentally  a  phenomenon  of  the  communication  and 
transmission  of  the  impulse  through  a  chain  of  elements.  Hence  there 
is,  between  the  simplest  and  the  most  complicated  actions  of  the 
nervous  system,  a  continuity  which  causes  the  second  to  take  origin 
from  the  first  by  an  insensible  gradation.  This  is  why  it  is  said  that 
the  function  of  the  nervous  system,  regarded  as  a  whole,  as  well  as 
in  detail,  is  mereh^  a  reflex  phenomenon.  The  reflex  act  is,  under  any 
circumstances,  the  simplest  image  which  we  can  employ  in  order  to 
characterize  this  totality  of  action. 

Ordinary  sense  of  the  word. — Yet,  in  current  language,  the  word 
reflex  is  used  to  designate  the  simplest,  the  most  uniform,  and  the 
most  circumscribed  nervous  acts,  both  as  regards  time  and  space,  as 
opposed  to  those  which  their  complication,  their  contingency,  their 
extension  in  the  nervous  system  and  their  duration  remove  from  the 
primitive  type  in  which  they  originate.  And  there  is  another  reason 
for  this. 

3.  Conscious,  subconscious  and  unconscious  reflexes. — The  simple, 
ordinary  reflex  has  the  aspect  of  a  purely  mechanical  movement  of 
transmission.  Consciousness  and  spontaneity  appear  to  be  totally 
absent  from  it  ;  on  the  other  hand,  this  spontaneity  and  this  con- 
sciousness seem  to  characterize  the  actions  which  require  the  inter- 
vention of  the  superior  portions  of  the  nervous  system,  and  especially 
of  the  cerebral  cortex.  Hence  the  reflex  act  has  been,  and  is,  opposed 
to  the  voluntary  act.  In  practice,  however,  this  opposition  is  based 
on  the  condition  that  it  is  not  regarded  as  absolute. 

Just  as,  in  the  order  of  movement,  we  proceed  from  the  simple 


218 


SYSTEMATIC  FUNCTIONS 


reflex  act,  from  the  ganglionic  or  spinal  reflex,  to  the  most  complex 
cerebral  act,  so,  from  this  extremely  perfected  act,  we  re-descend,  in 
the  psychical  order,  without  solution  of  continuity,  to  the  nervous  act, 
the  fundamental  base  of  all  the  others,  and  we  meet  with  traces  of 
this  consciousness  and  of  this  choice,  which  only  appear  in  their 
plenitude  and  in  a  marked  form  in  those  superior  systematizations 
which  are  effected  in  the  brain.  Three  chief  degrees  may  be  dis- 
tinguished in  this  succession,  corresponding  (1)  to  the  reflex  act,  (2) 
to  the  instinctive  act,  (3)  to  the  voluntary  act. 

4.  Elementary  reflex. — As  often  as  the  impulse  is  communicated 
from  one  nerve  element  to  another  which  follows  it,  there  is  reflexion 
of  this  impulse  in  the  most  general  sense  of  the  word,  whatever  may 

be  its  point  of  departure  and  its 
point  of  termination.  In  this  sense 
it  is  sometimes  said  that  the  im- 
pulse is  reflected  from  the  posterior 
roots  to  the  tracts  of  the  spinal 
cord,  in  conscious  impressions,  and 
from  these  latter  to  the  anterior 
roots  in  voluntary  movements, 
exactly  as  it  is  from  the  posterior 
roots  to  the  anterior  roots  in  the 
reflexes  properly  socalled. 

Centre  of  reflection. — The  locality 
in  which  the  impulse  changes  its 
route  and  is  reflected  is  usually 
called  the  ce?itre  of  reflection.  This 
region  is  clearly  that  in  which  the 
terminal  arborizations  of  the  first 
neuron  reach  the  initial  arboriza- 
tions of  the  second  neuron  ;  in  other 
words,  the  site  of  reflection  is  at  the 
union  of  the  two  neurons,  on  the 
hypothesis  of  an  elementary  reflex. 
In  proportion  as  elements  of 
association  are  superadded  to  this  primitive  system,  the  site  of  re- 
flection assumes  a  more  compHcated  aspect,  like  the  system  itself. 
The  word  centre,  so  often  made  use  of,  is,  as  is  obvious,  much  diverted 
from  its  etymological  meaning. 

5.  Experimental  data. — Anatomical  data,  incomplete  as  they  are, 
have  nevertheless  shown  us  above  according  to  what  complex  laws 
the  connexions  of  the  nerve  elements,  which  act  in  a  reflex  manner, 


Fig.  102. — Elements  of  association 
(in  heavy  type),  overlapping  of  the 
polar  fields  (after  M.  Duval). 

NS,  sensory  neui-on  ;  NAR  and  RA, 
radicular  motor  neuron  ;  NA^,  automere 
neuron  of  association  (situated  in  the 
same  half)  ;  NA2,  hetromere,  neuron  of 
association  (passing  from  one  half  to  the 
other  of_the  spinal  cord). 


PRIMARY    SYSTEMATIZATIONS  21 » 

are  effected.  Physiology,  for  its  part,  shows  us  what  transformations 
the  impulses  undergo  from  the  fact  of  their  passage  through  the  grey 
matter,  where  these  connexions  are  carried  out. 

We  will  now  consider  a  small  reflex  system  formed  of  a  segment  of 
the  spinal  cord  ;  this  system  is  supplied  with  its  sensory  and  motor 
nerves,  which  have  preserved  their  relations  mth  the  peripheral  organs 
(muscles  and  skin)  ;  stimulations  may  be  brought  to  bear  on  the  skin, 
on  the  sensory  nerve,  on  the  motor  nerve,  or  on  the  muscles,  and  all 
will  be  followed  by  different  results  ;  but  it  is  especially  when  the 
sensory  and  motor  nerve  are  stimulated  comparatively  that  the 
results  differ  and  are  most  instructive.  This  stimulation  induces  in 
the  nervous  path  which  leads  to  the  muscle  two  impulses,  the  one 
above,  the  other  below  the  grey  matter,  or  site  of  association. 

Retardation  of  the  impulse. — A  first  very  obvious  result  is  the 
retardation  which  attends  the  transmission  of  the  impulse  in  its 
progress  throvigh  the  grey  matter.  This  retardation  is,  indeed,  con- 
siderable, to  judge  by  the  results  of  experiments  on  animals.  In  the 
frog  it  may  amount  to  a  fourteenth  of  a  second.  It  has  been 
frequently  estimated  in  man  in  certain  prominent  reflexes,  such  as 
the  patellar  reflex.  As  regards  the  transmission  of  the  impulse  from 
nerve  to  nerve,  it  represents  a  latent  period  analogous  to  that  observed 
in  the  transmission  of  an  impulse  from  nerve  to  muscle. 

Intensity. — In  order  to  obtain  the  same  amount  of  contraction,  the 
intensity  of  the  stimulation  must  often  vary  considerably,  according 
as  it  is  applied  to  the  sensory  or  motor  nerve.  Hence  there  is,  in  this 
respect  also,  an  alteration  which  takes  place  in  the  site  of  transmission. 

To  put  the  matter  more  clearly,  the  results  of  the  stimulation  of  the 
motor  nerve  present  a  constancy  (at  least  relative)  which  is  not  pre- 
sent in  the  same  degree  in  those  which  follow  the  stimulation  of  a 
sensory  nerve.  This  is  expressed  by  saying  that  reflex  excitability  is 
variable.  If  may  be  inferred,  indeed,  that  the  conditions  on  which 
this  variability  depend  must  be  sought  in  the  locality  where  the 
sensori-motor  impulses  are  associated,  and  not  elsewhere.  In  prin- 
ciple, the  excitability  of  the  sensory  nerve  should  have  the  same 
fixity  as  that  of  the  motor  nerve  ;  but  the  grey  matter,  according 
to  circumstances,  is  hardly  ever  consistent  with  itself.  As  a  result 
of  the  changes  of  which  it  is  the  seat,  there  will  be  between  the  effects 
of  stimulation  above  and  below  the  site  of  reflection  a  predominance 
of  results  :  sometimes  of  sensory  stimulation,  which  is  rare  ;  some- 
times of  motor  stimulation,  which  is  the  rule  ;  exceptionally  there 
will  be  equality. 

Absorption  and    restitution.^ — To   judge  by  the  crude  results  of  ex- 


220 


SYSTEMATIC  FUNCTIONS 


periments,  the  ordinary  effects  of  sensory  excitation  are  markedly  a 
loss  of  its  intensity  in  its  passage  through  the  grey  matter.  This 
loss  is  probably  more  apparent  than  real.  In  any  case,  it  must  not 
be  concluded  that,  in  the  normal  exercise  of  function,  matters  are 
necessarily  arranged  in  this  fashion.  The  stimuli  which  we  cause  to 
penetrate  artificially  the  trunk  of  a  motor  or  sensory  nerve  are  not 
the  exact  equivalents  of  those  which  it  receives,  by  its  dendrites,  from 


've^-~^jiU~^ 


-tCereb.  cort. 


Pyr.  tract 1 


'Vucl.  of  the  bulb. 


'      %: Spinal  gangl. 


Cutan.  arbor. 


Musciil.  arbor. 


Fig.    103. — Cerebral  reflex  permitting  the  succession  of  se^'e^al  elementary  reflexes. 
Sensory  paths  in  blue  ;  motor  paths  in  red. 

the^special  organs  whose  duty  it  is  to  supply  them  to  it,  and  the  effects 
which  may  hence  result,  are  not  so  limited  as  those  which  ordinarily 
attract  our  attention  ;  but  the  analysis  which  they  allow  us  to  make 
is  instructive.  We  observe  that  the  impulse  is  sometimes  absorbed 
and  retained  by  the  grey  matter  and  the  systems  which  it  connects, 
while  at  other  times,  on  the  contrary,  it  is  permitted  such  unlimited 
action  that  it  exhausts  its  stores  of  force. 


PRIMARY    SYSTEMATIZATIONS 


221 


-  Brain 


-  Cerebellum 


Form  of  the  movements. — The  ensuing  movements  may  be  very 
different,  according  to  whether  the  sensory  or  the  corresponding 
motor  root  is  stimulated.  When  applied  to  the  motor  nerve,  the 
stimulation  induces  a  simultaneous  contraction  of  all  the  muscles  to 
which  it  is  distributed.  When  applied  to  the  sensory  nerve,  in  pass- 
ing through  the  grey  matter  it  undergoes  a  rearrangement  which 
gives  a  definite  direction  to  the  movement  ;  mthout  taking  into 
account  that  it  may  be  diffused  in  the  area  of  the  neighbouring  motor 
nerves. 

6.  General  direction 
of  the  current  of  impulse  ; 
method  of  its  determina- 
tion.— In  order  to  deter- 
mine the  direction  in 
which  the  impulse  is 
transmitted,  in  the  differ- 
ent nerves  and  in  the 
systems  which  they  con- 
stitute, two  methods  are 
available  :  the  one  in- 
direct, the  other  direct. 

The  indirect  method 
consists  in  taking  as 
controls  certain  pheno- 
mena of  movement  or  of 
sensation  of  which  the 
situation  in  the  animal 
experimented  upon  with 
regard  to  the  stimulated 
nerve  has  been  noticed. 

The  direct  method  con- 
sists in  collecting,  frbm 
the    nerves     themselves, 

indices  of  their  activity  in  the  different  points  of  the  course  supposed 
to  be  traversed  by  the  impulse,  by  verifying  their  negative  variation 
or  current  of  action.  It  is  true  that  it  is  necessary  to  mutilate  the 
nerve  at  the  very  point  where  it  is  desired  to  collect  its  electrical 
current. 

The  information  furnished  by  the  two  methods  is,  further,  con- 
cordant and  mutually  complete. 


.  Sensory  root 


Fi>)re  of  ass. 


Muscul.  bundle 


Fig.   104. — Convergence     of  impulses     of     different 
sources  on  a  radicular  motor  element. 

Overlapping  of  the  polar  fields. 


Irreversibility  of  the  reflex    cycle, — The  posterior  and  anterior  roots  having 


222  SYSTEMATIC  FUNCTIONS 

been  laid  bare,  the  first  are  connected  with  a  stimulating  apparatus  (sledge  in- 
duction apparatus  of  du  Bois)  and  the  second  to  a  galvanometer.  Every  time 
that  the  central  end  of  the  posterior  root  is  stimiJated  there  will  be  a  galvano- 
metric  deviation  as  regards  the  anterior  root.  The  galvanometer  points  out,  as 
would  the  muscle  (but  in  a  more  direct  manner),  that  the  stimulation  of  the 
posterior  root  is  transmitted  to  the  anterior  root. 

Let  the  arrangement  be  now  reversed,  as  has  been  effected  by  Mislawsky,  by 
connecting  the  anterior  root  with  the  induction  coil  and  the  posterior  root  with 
the  galvanometer.  Stimulation  of  the  anterior  root  will  not  produce  deviation 
of  the  galvanometer  which  is  connected  with  the  posterior  root.  As  a  matter 
of  fact,  however,  stimulation  travels  to  the  spinal  cord.  If  this  root  be  detached 
froin  the  spinal  cord  in  order  that  its  central  end  may  be  connected  with  the 
galvanoineter,  a  deviation  at  the  instant  of  stimulation  will  be  observed.  It  is, 
indeed,  on  the  resialts  of  experiments  of  this  kind  that  the  common  conductivity 
of  nerve  fibres  is  based.  But  if  the  in:ipulse  received  by  a  neuron  can  thus  freely 
traverse  it  in  both  directions,  this  impulse  is  transmitted  from  one  neuron  to 
another  in  one  direction  only,  as  is  shown  by  the  experiment  of  Mislawsky. 

According  to  the  terms  ordinarily  iised,  the  impulse  proceeds  from  the  terminal 
or  collateral  ramification  to  the  dendrites  of  other  neurons  (when  these  neurons  are 
connected  amongst  themselves),  and  not  conversely.  It  may  also  be  said  :  it 
proceeds  from  an  emissive  to  a  receptive  pole,  but  never  from  a  receptive  to  an  emissive 
pole.  There  is  here  manifestly  an  arrangement,  the  natiu"e  of  which  is  unknown, 
which  hinders  the  impulse  from  going  backwards  from  the  second  to  the  first, 
and  which  determines  the  direction  of  the  currents  of  stiinvilation  through  the 
nervous  system.  It  may  be  coinpared  to  the  valves  of  the  circulatory  system 
which,  situated  in  the  heart,  imprint  on  the  movement  of  the  blood  a  definite 
direction,  while  this  movement  is  free  as  regards  its  direction  in  all  the  I'est  of 
the  system. 

Other  examples. — If  a  posterior  root  be  stimvilated  and  a  derivation  of  the 
currents  of  action  of  the  spinal  cord  be  received  (after  section  of  the  cord  below 
the  medulla  oblongata),  a  deviation  is  observed.  If  an  anterior  root  be  stimu- 
lated, there  is  no  deviation.  If  the  spinal  cord  be  stimulated  and  the  currents 
in  the  anterior  root  be  received,  there  is  deviation. 

All  these  facts  agi'ee  with  the  former  experiments  of  Magendie,  which,  by  the 
motor  and  sensory  effects  of  stimulation  of  the  roots,  have  shown  the  general 
direction  of  the  propagation  of  this  excitation.  The  new  fact  wliich  has  been 
established  is  the  localization  of  the  directive  force  in  the  grey  matter,  and 
more  precisely,  at  the  point  of  vinion  of  the  poles  of  ojDposite  denominations  of  the 
neiirons.  It  should  be  observed  that  this  directive  condition,  which  is  an  im- 
portant function  of  the  nerve  centres,  is  not  localized  in  the  nerve  cells. 

Directing  organ. — The  nerve  cells  are  generally  situated  in  the  immediate 
neighbourhood  of  the  polar  arborizations  of  the  neurons  ;  whence  it  follows  that, 
in  considering  only  the  abortive  indications  of  experiment,  the  role  of  organs 
directive  of  excitation  may  be  attributed  to  thein  as  well  as  to  these  arborizations 
themselves.  It  is  thus  in  the  ganglia  of  the  great  sympathetic,  as  well  as  in  the 
spinal  cord  and  brain ;  and  this  has  given  rise  to  the  idea  that  the  nerve  cells 
are  the  true  centres  in  the  sense  which  is  attached  to  the  word.  There  are,  how- 
ever, neurons  whose  original  cells  are  situated  at  a  great  distance  from  their 
polar  extremities.  These  are  the  nerves  of  cvitaneous  sensation,  which  pass,  as 
is  well  known,  through  the  spinal  ganglia  situated  on  the  posterior  roots.  If 
the  spinal  cell  is  a  reflex  centre,  it  should  behave  as  does  every  other  reflex  centre, 
that  is  to  say,  should  permit  the  impulse  to  pass  only  in  one  direction,  from  the 
skin  to  the  spinal  cord,  and  not  conversely.  But  no  experiment  is  known  which 
proves  that  this  is  the  case,  and  it  is  on  the  contrary  admitted  without  contradic- 


PRIMARY    SYSTEMATIZATIONS  223 

tion  that  the  impulse  may  pass  from  the  post-ganglionic  segment  to  the  pre- 
ganglionic segment  of  the  sensory  nerve.  Another  experiment,  iierformed  by 
Langley,  is  equally  significant.  Wlien  certain  ganglia  of  the  great  sympathetic 
are  subjected  to  the  action  of  nicotine,  the  pre-ganglionic  segment  becomes 
inexcitable,  while  the  post-ganglionic  joreserves  its  excitability  ;  in  other  words, 
when  nicotine  is  brought  in  contact  with  a  ganglion  of  tlie  great  sympathetic  it 
prevents  the  impulse  from  jDassing  through  it.  If  this  experiment  be  rejDeated 
on  a  spinal  ganglion,  the  result  is  no  longer  the  same  ;  the  two  segments,  pre- 
and  post-ganglionic,  remain  excitable.  Thus  the  physiological  reagent  em- 
ployed, nicotine,  meets  in  the  ganglia  of  the  great  sympathetic  with  a  condition 
of  activity  which  it  does  not  exj^erience  in  the  spinal  ganglia.  As  nerve  cells 
exist  in  both,  this  condition  is  not  due  to  the  cell  ;  as  polar  connexions  exist  in 
the  first  and  not  in  the  second  (at  least,  so  far  as  concerns  the  transmission  of 
cutaneous  impressions  to  the  spinal  cord),  it  is  reasonable  to  assume  that  these 
polar  connexions  are  the  organ  on  which  the  reagent  employed  acts. 

7.  Dispersion  of  the  excitation  ;  its  laws. — The  stimulation  of  a 
sensory  region,  or  of  a  sensory  nerve,  is  reflected  in  the  grey  matter 
of  the  spinal  cord,  in  order  to  return  to  the  muscles,  through  the 
motor  nerve.  According  to  the  intensity  of  the  stimulation,  the 
resulting  movements  will  be  localized  or  more  or  less  generalized.  The 
dispersion  of  the  excitation  follows  certain  laws  which  have  been 
formulated  by  Pfliiger,  whose  name  they  bear,  but  which  are  based 
on  the  results  separately  ascertained  or  recognized  by  a  number  of 
earlier  authors  (Herbert-Mayo,  Calmeil,  etc.,  etc.)  :  (1)  //  the  7novements 
are  unilateral,  they  take  place  on  the  same  side  as  the  sensory  nerve  stimu- 
lated ;  (2)  //  the  movements-  are  bilateral,  they  occur  in  symmetrical 
muscles  ;  (3)  Bilateral  movements  following  a  unilateral  stimulation 
are  of  the  same  form,  but  stronger  on  the  side  of  stimulation  ;  (4)  The 
transmission  of  the  impulse,  when  it  is  generalized,  may  be  performed 
just  as  icell  from  the  cephalic  extremity  to  the  caudal  extremity  as  in- 
versely. This  fourth  law  has  taken  the  place  of  another  incorrectly 
formulated,  according  to  which  the  propagation  of  the  impulse  can 
only  be  effected  from  the  cephalic  extremity. 

According  to  these  facts,  the  impulse,  in  extending  over  the  nervous 
system,  would  appear  to  invade  first  of  all  the  nearest  regions,  and 
then  those  more  remote  ;  as  if  it  w^ere  necessary  for  it  to  overcome 
a  certain  resistance  which  tends  to  limit  its  extension,  and  it  traverses 
a  longer  or  shorter  route  according  to  its  initial  intensity  or  the  state 
of  excitability  of  the  grey  matter.  This  is  the  simple  law  of  its 
propagation  and  of  its  dispersion  verified  on  an  apparatus,  the  organi- 
zation of  which  is  itself  relatively  simple,  viz.,  the  spinal  cord  sepa- 
rated from  the  medulla  oblongata ;  but  it  must  not  be  forgotten  that 
the  exercise  of  function  creates  routes  of  less  resistance,  by  ivhich  the  most 
remote  organs  may  themselves  transmit  the  impulse,  to  the  exclusion  of 
other  routes  situated  nearer.     Applicable  to  cutaneous  or  artificial 


224 


SYSTEMATIC  FUNCTIONS 


excitation  of  sensory  nerves,  the  preceding  laws  would  no  longer  apply- 
as  regards  the  detail  of  functions. 

If  the  medulla  oblongata  is  alone  preserved,  it  is  in  it  that  the 
impulses  tend  to  become  concentrated,  and  it  is  it  on  which  the  duty 
is  imposed  of  rearranging  and  distributing  them.  Should  the  brain 
take  part  in  the  process,  every  trace  of  the  preceding  simplicity 
disappears. 

Numerous  exceptions. — Even  in  operating  on  the  separated  sjjinal  cord,  the 
laws  of  Pfliiger  are  subject  to  numerous  exceptions,  as  lias  been  remarked  by 
many  observers,  and  particularly  by  Sherrington,  who  has  made  a  special  study 
of  the  question.  These  so-called  laws  can  only  be  regarded  as  schemes  which 
must  be  adjusted  to  each  individual  case.  It  is  easily  understood,  indeed,  that 
special  functions,  such  as  walking,  vision,  etc.  which  involve  combinations  of 
movements,  some  alternative,  others  simultaneous,  some  symmetrical,  others 
unsymmetrical,  cannot  be  compressed  into  such  simple  formula^.  These 
formulsp  express  a  tendency,  but  nothing  more. 

7.  Classification  of  refxexes. — Longet  has  gathered  together  a  certain 
number  of  reflex  acts  which  he  has  arranged  in  categories,  by  taking 
as  a  foundation  the  starting-point  of  the  excitation  and  the  point  in 
which  the  motor  reaction  terminates.  Two  nerve  systems  are  usually 
distinguished,  corresponding  to  two  orders  of  functions  and  of  organs  : 
the  one  concerned  with  nutritive  acts,  the  other  with  external  rela- 
tions. The  examples  collected  by  Longet  show  that  each  of  these 
systems  contains  intrinsic  reflex  cycles  ;  but,  further,  that  each  one 
is  connected  with  the  other  :  sensory  nerves  of  the  one  with  motor 
nerves  of  the  other,  and  conversely. 

Let  N  represent  nutrition,  R  external  relations,  and  let  the  direction 
of  the  propagation  of  the  impulse  be  indicated  by  an  arrow.  There 
are  four  possible  complications  :  NN,  RR,  NR,  RN.  The  best  known 
examples  may  be  arranged  in  the  form  of  a  table.     These  examples 


Elements  of  the 
Cycle. 


N->N 


R->R 


N->R 


R^N 


Sensory  Excitatious. 


Arrival    of   the    aliments 
the  digestive  tube. 


Motoi"  Reactions. 


Movements  of  the  oesopha- 
gus, of  the  stomach  and  the 
intestine. 


Abrupt  movement  menacing  Blinking  of  the   eyelids, 

the  eye. 


Presence  of  worms  irritating  Convulsions  of  the  limbs, 

the  intestine. 


Painful    excitations    of    the  Generalized     \-ascular     con- 

skin,  striction. 


PRIMARY    SYSTEMATIZATIONS  225 

could  be  multiplied,  to  infinity.  It  would  be  easy  to  make  numerous 
divisions  and  subdivisions  for  each  one  of  these  categories,  correspond- 
ing to  different  orders  of  sensation  and  of  motor  reaction.  The  number 
of  combinations  would  increase  in  such  a  way  as  to  defy  every  descrip- 
tion and  schematic  representation.  It  is  easier  to  say  that  every 
sensory  element  can  he  brought  into  reflex  relation  icitJi  every  motor 
element,  for  the  exercise  of  the  multiple  functions,  whether  of  detail 
or  of  the  whole,  by  which  life  is  maintained. 

9.  Reflex  centres  of  the  spinal  cord. — Reflex  centres  are  found 
wherever  the  grey  matter  occurs.  The  spinal  cord  contains  them 
throughout  its  length.  Physiology  proves  this  by  showing  that,  after 
isolation  of  each  of  the  metameric  segments  of  this  organ,  the  impulse 
finds  a  way  across  it,  in  order  to  proceed  from  the  posterior  to  the 
anterior  root.  Anatomy  confirms  this  fact,  by  showing  that  the 
terminal  arborizations  of  the  neurons  of  the  first  come  in  contact 
with  the  initial  arborizations  of  those  of  the  second. 

Principal  medullary  centre  ;  Goll's  Nucleus. — Physiology  also  has 
long  demonstrated  (even  in  the  dog  and  in  the  frog)  one  or  more 
reflex  centres  more  important  than  the  rest,  situated  in  the  superior 
portion  of  the  spinal  cord,  and  indeed  encroaching  on  the  medulla 
oblongata.  Experiments  performed  long  ago  have  shown  what  an 
advantage  it  is  for  sensory  impulses  to  pass  through  these  elevated 
regions  in  order  to  reach  the  nerves  of  organic  life  (pupillary  nerves, 
vaso-motors)  with  certainty  and  efficiency.  The  somewhat  more 
recent  experiments  of  Rosenthal  and  Mendelsohn  have  shown  that  it 
is  the  same  as  regards  those  which  reach  the  motor  nerves  of  the 
limbs  (nerves  of  the  so-called  life  of  relation)  ;  they  do  not  exert  all 
their  effects,  from  the  reflex  point  of  view,  except  by  passing  through 
the  nucleus  of  Goll  situated  in  the  superior  portion  of  the  spinal  cord, 
and  here,  also,  anatomy  confirms  the  physiological  fact  by  enabling 
us  to  follow  the  intramedullary  prolongations  of  the  posterior  roots, 
whose  ascending  branches  (giving  off  the  already  mentioned  collaterals 
on  their  course)  ascend  to  Goll's  nucleus  in  order  to  seek  those  paths 
which  bring  back  the  impulse  to  the  organs  of  the  motor  nerves. 
There  is  here  an  important  reflex  centre. 

10.  Encephalic,  subcortical  centres. — The  opto-striate  bodies  are 
also  centres  of  this  nature  of  a  higher  function  and  more  completely 
organized,  but  still  reflex,  presiding  over  instinctive  movements  inter- 
mediate between  reflex  automatism  and  the  contingent  demeanour  of 
the  voluntary  movements. 

11.  Reflex  cortical  centres. — The  cerebral  cortex  acts  as  a  reflex 
centre  under  many  different  circumstances.     The  acts  (of  involuntary 

P.  Q 


226  SYSTEMATIC  FUNCTIONS 

nature)  of  the  deeply  seated  organs  have  in  it  their  automatic  regu- 
lative centres.  The  most  complicated  acts  of  the  life  of  relation  can 
take  place,  like  the  preceding,  in  an  automatic  fashion,  without 
direct  participation  of  individual  consciousness  and  will. 

The  condition  of  the  reflexes  in  pathology. — It  has  long  been  observed 
clinically  that,  in  cases  of  more  or  less  total  interruption  of  the  conducting  fibres 
of  the  sjiinal  cord,  reflex  movements  exist  in  the  inferior  limb,  and  indeed  are 
often  increased.  These  clinical  facts  are  satisfactorily  exjolained  by  the  definite 
results  of  physiological  experiments.  But  in  looking  at  them  more  closely,  it 
is  necessary  to  allow  that  the  conditions  on  both  sides  are  not  so  identical  as  was 
fornierly  supposed  to  be  the  case. 

Medullary  reflexes. — Of  the  old  conclusions  which  had  been  admitted  without 
question,  this  one  still  remains  :  these  reflex  movements,  those  which  are 
normal  as  well  as  those  provoked  by  excitations  of  the  sensory  localities  or  sen- 
sory nerves,  may  be  observed,  even  in  man,  after  complete  interruption  of  the 
spinal  cord.  They  are  also  observed  in  the  ape  after  experimental  section  of 
the  cord.  Bvit  instead  of  being  very  quickly  recovered,  as  in  the  dog  and  the 
frog,  and  of  becoming  exaggerated  as  in  these  animals,  they  may  remain  in  abey- 
ance during  days  or  weeks,  only  reappearing  slowly  and  remaining  feeble. 

Cerebral  reflexes. — The  movements  known  as  reflex,  on  account  of  their 
automatic  occurrence,  are  not  the  exclusive  attribute  of  the  sj^inal  cord,  and  of 
its  bulbar  prolongation,  while  voluntary  movements  would  only  appertain  to 
the  brain,  as  has  been  long  believed.  All  the  areas  of  the  grey  matter,  wherever 
found,  including  the  cerebral  cortex,  are  capable  of  automatically  reflecting  impulses  ; 
this  is  the  primary  function  of  the  grey  matter.  To  this  function,  the  simplest 
which  effects  movements  adapted  to  a  general  end  and  following  a  simple  general 
law,  is  superadded  another,  which  is  in  reality  nothing  but  its  perfected  expres- 
sion, that  of  producing  varied  movements  according  to  contingent  indications, 
movements  which  are  described  as  voluntary.  This  function  is  not  the  attribute 
of  grey  matter  of  a  particular  kind,  and  in  consequence  privileged,  but  depends 
vipon  a  more  complete  union  of  the  nerve  grovips  amongst  themselves.  The 
privilege  of  the  grey  matter  of  the  cortex  consists  in  the  number  and  the  power 
of  its  associations,  which  ensure  the  exercise  of  that  which  is  known  as  intelli- 
gence and  will.  Should  these  associations  be  resolved  into  their  elementary  com- 
ponent systems,  the  brain  will  then  operate  as  a  reflex  or  automatic  organ.  Not 
only  is  the  brain  not  deprived  of  a  reflex  function,  but  the  cerebral  reflexes  are 
the  most  numerous  of  all,  on  account  of  the  large  number  of  elementary  systems 
which  enter  into  its  constitution. 

Post-hemiplegic  contraction. — It  is  often,  but  not  invariably  observed,  that 
in  hemiplegic  patients  an  augmentation  of  the  muscular  tone  of  the  paralysed 
limbs  occm's,  which  must  be  regarded  as  an  instance  of  a  reflex  phenomenon 
(tonic  reflex  and  no  longer  clonic  reflex).  Its  explanation  is  less  simple  than  that 
of  the  preceding  facts.  Indeed,  it  differs  from  them  esj^ecially  in  this,  that  the 
total  interruption  of  the  spinal  cord  is  not  only  not  a  determining  condition,  but 
renders  impossible  the  onset  of  the  phenomenon.  Many  explanations  of  this 
phenomenon  have  been  proposed,  of  which  each  is  based  on  some  hypothesis 
concerning  the  function  of  the  conducting  fibres  which  unite  the  grey  masses  or 
superior  svirfaces  to  the  grey  columns  of  the  spinal  cord  ;  all  agree  in  this,  that 
there  is,  from  the  fact  of  the  lesion  which  has  produced  hemiplegia,  a  loss  of 
some  antagonistic  force  which,  being  no  longer  counterbalanced,  leaves  the  field 
free  to  reflex  motor  action.  By  some,  this  antagonism  is  regarded  as  piu'ely 
motor  and  as  being  exercised  between  the  muscular  forces  spared  by  the  para- 


PRIMARY    SYSTEMATIZATIONS  227 

lysis,  for  the  benefit  of  those  wliose  centres  have  been  the  best  preserved.  It 
has  affected,  for  example,  the  extensors  and  the  flexors  unequally,  the  first  being 
more  seriously  involved  than  the  second  ;  in  this  case  the  member  contracts. 
By  others,  the  antagonism  is  looked  upon  as  existing  between  the  two  nerve 
forces,  the  one  of  stimulation  the  other  of  inhibition,  which  are  more  and  more 
firmly  believed  to  co-exist  in  the  nervous  system,  represented  as  they  are  by 
fibres  wlaich  are  individually  distinct,  although  often  mingled  in  the  tracts.  From 
the  brain  an  inhibitory  influence  would  descend  into  the  spinal  cord  by  way  of 
the  pyramidal  tracts.  Degeneration  of  the  latter,  by  supjDressing  this  influence, 
would  leave  the  field  free  to  motor  impulses,  and  would  in  this  way  result  in 
contraction.  But,  as  regards  the  site  at  wliich  these  impulses  are  reflected, 
some  would  place  it  in  the  S2")inal  cord,  as  in  the  old  theory  of  the  reflex  (P.  Marie). 
For  these  the  necessary  and  sufficient  condition  of  the  contraction  is  the  inter- 
ruption of  the  pyramidal  tracts.  Others  would  look  upon  these  impulses  as 
ascending  to  the  brain,  whence  they  would  redescend  by  special  paths,  the 
cerebro-iDonto-cerebellar  tracts,  in  order  to  reach  the  spinal  cord.  For  these 
latter  a  necessary  condition  of  the  contraction  would  be  not  only  the  destruc- 
tion of  the  pyramidal  tract,  but  also  the  conservation  of  the  cerebro-ponto- 
cerebellar  tracts. 

B.     SUSPENSION    OF    THE    EXCITATIONS;    ACTION    OF    ARREST    OR 

INHIBITION 

In  the  reflex  act,  the  excitation  of  an  element  is  communicated  to 
one  or  several  other  elements  which  follow  it.  In  the  inhibitory  act, 
the  effect  of  an  excitation  is  to  suspend,  or  to  render  momentarily  impos- 
sible, this  transmission  of  the  imqndse  from  one  element  to  one  or  several 
other  elements. 

1.  Its  scheme. — The  reflex  scheme  presupposes  at  least  two  neurons, 
indeed  two  groups  of  neurons,  connected  in  succession. 

The  scheme  of  inhibition,  such  as  it  may  be  represented  according 
to  the  known  facts  which  have  served  to  prove  its  existence,  pre- 
supposes at  least  three  of  these  ;  two  of  them  being  arranged  end  to 
end,  in  order  to  form  the  fundamental  reflex  arc  ;  towards  their  point 
of  association  a  third  converges,  the  function  of  which  is  to  hinder 
the  transmission  of  the  impulse  from  the  first  to  the  second.  It  is 
unnecessary  to  add  that  these  are  purely  imaginary  representations, 
and  that  in  reality  we  deal  with  complex  nerve  masses,  which  we  en- 
deavour to  reduce  to  their  most  simple  type,  but  without  ever  being 
sure  of  succeeding  in  doing  so. 

Its  seat. — The  locality  in  which  this  inhibitory  phenomenon  takes 
place  is,  once  again,  the  grey  matter  wherever  it  occurs  (great 
sympathetic  ganglion,  grey  axis  of  the  spinal  cord  and  of  the  medulla 
oblongata,  ganglia  and  cortex  of  the  brain,  etc.).  And  amongst  the 
alterations  that  this  substance  impresses  on  the  progress  of  impulses, 
this  is  not  one  of  the  least  remarkable.  At  the  same  time  as  the  seat 
of  the  phenomenon,  it  is  necessary  to  define  the  sense  of  the  word  ;  it 
is  important  to  ascertain  wdth  exactitude  the  conditions  which  must 


228 


SYSTEMATIC  FUNCTIONS 


be  fulfilled  in  order  that  it  may  occur  and  which  enable  it  to  be  dis- 
tinguished from  other  apparently  similar  phenomena. 

Apparently  paradoxical  datum. — Inhibition,  nerve  arrest,  is  not  a 
fact  whose  existence  necessarily  occurs  to  the  mind.  On  the  contrary, 
at  the  first  glance  this  fact  appears  to  be  paradoxical,  and  it  is  experi- 
ment which  enables  us  to  realize  it.  It  is  accepted  as  an  axiom  that 
all  muscular  activity  implies  (in  the  normal  performance  of  function 

in  the  organism)  a  nervous  activity  which 
presides  over  it.  And  further,  it  has  been 
accepted  for  a  long  time,  as  a  necessary  con- 
sequence of  this  fact,  that  muscular  repose 
implies  repose  of  the  nervous  system.  But 
experiment  has  shown  (and  this  is  the  very 
essence  of  the  inhibitory  phenomenon)  that 
muscular  repose  may  he  the  consequence  of 
nerve  activity.  In  other  words,  the  excita- 
tion of  certain  nerves  may  be  rendered 
evident  by  the  activity  of  the  muscles  with 
which  they  are  in  mediate  or  immediate  re- 
lationship ;  but,  further,  the  excitation  of 
certain  other  nerves  may  be  made  manifest 
by  the  stoppage  or  the  non-execution  of  the 
movement  of  the  muscles  with  which  they 
have  certain  relations,  regarded  as  mediate. 
An  example  is  necessary  to  support  this 
distinction. 

Example. — The  heart  receives  from  the 
spinal  cord,  through  the  great  sympathetic, 
nerves  whose  stimulation  is  rendered  evident  by  exaggeration  of  its 
movements  (beating  or  cardiac  systole) ;  it  receives  others  from  the 
medulla  oblongata  by  way  of  the  pneumogastric,  whose  excitation  is 
followed  by  the  slowing  or  temporary  stoppage  of  its  movements. 
These  nerves  supplied  the  first  known  example  of  nerve  arrest.  The 
fact  was  observed  by  the  brothers  Weber  (1845)  and  was  afterwards 
confirmed  by  numerous  observers  ;  not,  it  is  true,  without  a  prolonged 
discussion  concerning  its  exact  signification. 


Fig.  105. — Diagram  of  the 
antagonistic  action  of  the 
excito-motor  and  inhibi- 
tory nerves  on  the  terminal 
nerves. 

This  action  is  exerted  by  the 
connexions  of  these  different 
elements  between  themselves 
in  the  grey  matter  of  the  gangUa 
or  motor  nuclei. 


Numerous  meanings  attached  to  the  word  inhibition. — Whenever  a  new  pheno- 
menon takes  its  place  in  a  science,  a  new  and  special  term  is  necessary  in  order 
to  designate  it.  Suspension  of  the  activity  of  an  organ  by  the  arousing  of 
activity  in  a  nerve  supplying  it,  was  first  called  "  stoppage."  Later,  Brown- 
Sequard  proposed  the  term  "  inhibition,"  of  which  the  great  success  is  well  known. 
Brown-Sequard  made  no  attempt  to  narrowly  define  the  characters  of  the  j^heno- 


PRIMARY  SYSTEMATIZATIONS  229 

nienon,  but,  under  the  name  of  inhibition,  he,  on  the  contrary,  gathered  together 
all  tlie  facts  which  had  a  near  or  remote  analogy  with  it. 

Instead  of  a  clearly  defined  signification,  the  new  word  assumed  a  meta- 
phorical and  indeterminate  meaning. 

Inhibition  and  paralysis. — However,  in  his  definition  of  inhibition,  the  pre- 
ceding author  still  maintained  (at  least,  theoretically,  if  he  did  not  succeed  in 
justifying  it  by  the  examples  he  brought  forward)  the  idea  of  the  contrast  exist- 
ing between  the  exciting  nature  of  the  cause  and  the  depressive  aspect  of  the 
result.  It  may  be  said,  indeed,  that  he  exaggerated  it,  by  seeing,  in  every  loss 
of  function,  the  effect,  not  of  a  destruction,  but  of  a  stimulation.  But  for  some 
years  this  particular  meaning  has  been  steadily  losing  ground.  It  is  possible 
to  read  in  a  number  of  works  tliat  curare  inhibits  motor  nerves,  that  chloroform 
inhibits  sensation,  etc.^  To  designate  these  toxic  jDhenomena  and  other  similar 
ones  which  involve  a  loss  of  function,  a  word  has  for  long  been  available,  and  a 
very  definite  one,  namely  paralysis,  and  this  is  the  only  one  which  is  appropriate. 
By  closely  assimilating  inhibition  and  paralysis,  the  very  idea  which  this  new 
word  (inhibition)  was  intended  to  indicate  disappears.  In  order  to  prevent  this 
confusion,  it  is  necessaiy  to  return  to  the  experimental  datum  which  lies  at  the 
foundation  of  the  concejation  of  inhibition.  This  appellation  will  he  given  to 
every  phenomenon  reproducing  the  characters  and  the  essential  conditions  of  stoppage 
of  the  heart  by  the  stimulation  of  the  vagus  nerves.  Among  the  numerous  pheno- 
mena to  which  the  name  of  inliibition  has  been  given  there  is  a  certain  number 
which  has  some  analogy  to  the  stoppage  of  the  heart,  along  with  many  others 
which  have  no  connexion  with  it.  It  is  necessary  to  be  aware  that  the  classifica- 
tion of  the  facts  from  this  point  of  view  is  often  uncertain  and  difficult  to  effect. 
While  waiting  tintil  this  classification  may  be  rendered  exact,  it  is  desirable  to 
be  careful  in  the  emplojanent  of  the  word. 


Fig.    106. — Stoppage  of  the  heart  by  stimulation  of  the  vagus  in  the  turtle  (laboratory 

tracing). 
Latent   period   of   some   duration.     Post-compensatory   exaggeration    of  Jthe   systoles    after 
stoppage. 

It  is  necessary  also  to  be  aware  that,  in  current  literatui'e,  it  includes  pheno- 
mena, doubtless  analogous,  but  which  nevertheless  differ  greatly  the  one  from 
the  other. 

Inhibition  and  shock. — When  a  shock  of  a  certain  violence  acts  on  a  tissue 
(nervous  tissue  principally),  a  temporary  alteration  may  occur  in  it  which  renders 
it  unable  to  manifest  its  activity.  This  is  seen  in  cerebral  concussion  as  well  as 
in  spinal  or  nervous  concussion.  This  inability  to  react  is  obviously  of  the 
nature  of  paralysis  induced  by  direct  loss  of  function.  Hence  it  is  wrongly  regarded 
as  an  inhibition.  In  any  case  the  mechanism  of  the  phenomenon,  and  the  appro- 
priateness of  its  designation,  are  open  to  discussion. 

But  the  jaathological  phenomenon  to  which  the  name  of  shock  has  been  given 
may  present  different  forms,  causes  and  mechanism.  As  the  result  of  serious 
wounds  involving  organs  which  are  remote  from  the  centres,  a  severe  depression 
of  the  whole  nervous  system  sometimes  ensues  ;  and  it  is  reasonably  explained 
by  an  influence,  probably  irritative,  which,  emanating  from  the  wound,  reaches 

1  The  word  is  even  employed  by  certain  chemists,  for  whom  sulphtiric  acid  would 
inliibit  sulphate  of  soda,  and  reciprocally. 


230  SYSTEMATIC  FUNCTIONS 

the  nervous  centres  by  the  way  of  the  sensory  nerves.  This  case  resembles 
inhibition  such  as  it  is  defined  in  physiology  (an  activity  which  prevents  the 
manifestation  of  other  activities).  In  this  special  case,  but  not  in  that  in  which 
the  nervous  organ  is  directly  wounded,  it  is  right  to  speak  of  inhibition. 

Inhibition  and  fatigue. — When  the  nerves  of  an  organ  have  been  stimulated 
severely  and  for  a  long  time,  the  organ  becomes  for  a  certain  period  incapable 
of  functional  activity.  This  functional  incajDacity  is  not  jaaralysis,  but  fatigue. 
Some  observers  would  not  hesitate  to  describe  this  jDhenomenon  also  as  inhibi- 
tion. This  is  a  new  confusion  added  to  the  preceding.  Paralysis,  fatigue,  and 
inhibition  resemble  one  another  doubtless,  in  that  they  manifest  themselves  by 
an  inactivity  (persistent  or  temporary)  of  organs  ;  but  on  this  account  the  three 
terms  are  not  synonyms  expressing  inactivity.  Each  one  of  the  three  has  its 
exact  signification  ;  each  one  indicates  an  inactivity  of  a  special  kind,  of  a  special 
mechanism.  It  is  as  if,  the  effect  being  fundamentally  the  same,  the  conditions 
of  its  production  differ  absolutely  in  the  three  cases,  and  the  special  terms  made 
use  of  to  characterize  the  three  phenomena  are  meant  to  point  out  the  conditions 
on  which  they  depend. 

2.  Analysis  of  the  system. — It  is  now  tolerably  easy  to  show  that 
the  scheme  of  innervation  of  the  heart  corresponds,  in  its  main  out- 
lines, to  that  which  we  have  traced  above  with  regard  to  a  system 
capable  of  producing  inhibition.  The  heart  possesses  ganglia  which 
are  nothing  else  than  scattered  masses  of  grey  nervous  matter. 
From  these  ganglia  short  neurons  arise,  which  proceed  to  the  myo- 
cardium ;  these  are  the  motor  nerves,  properly  so  called,  of  the  heart. 
In  these  ganglia  terminate  neurons  of  great  length  coming,  some  from 
the  spinal  cord,  others  from  the  medulla  oblongata,  which  form  with 
the  grey  matter  connexions  of  such  nature  that  the  stimulation  of 
both  has,  so  to  say,  oj^posite  effects  :  that  of  the  first  is  transmitted 
(not  without  modification)  to  the  motor  elements  of  the  heart  ;  that 
of  the  second  produces  an  obstacle  to  such  a  transmission,  and  deprives 
the  myocardium  of  its  habitual  source  of  excitation,  whence  its 
temporary  stoppage. 

Of  the  three  portions  which  are  regarded  as  necessary,  the  first 
suppresses  one,  and  causes  the  inhibitory  nerve  with  the  motor  nerve 
to  converge  on  the  muscle,  to  which  each  one  of  the  two  would  convey 
an  inverse,  or  reciprocally  antagonistic,  influence  ;  the  others  sup- 
press two  and  only  admit  a  single  element,  alternatively  motor  or 
inhibitory,  according  to  circumstances.  But  facts  contradict  this 
manner  of  viewing  the  matter. 

Distinct  existence  of  inhibitory  nerves. — Inhibition  (arrest  by  ex- 
citation) necessarily  depends  on  conditions  which  appertain  either  to 
the  stimulating  agent  or  to  the  substance  excited.  Therefore  it  does 
not  depend  on  the  conditions  of  the  excitation.  It  is,  in  fact,  produced 
by  stimuli,  which  are  the  very  same  as  those  which  put  the  motor 
nerves  in  action.     It  ceases  to  be  produced,  on  the  other  hand,  with 


PRIMARY  SYSTEMATIZATIONS 


231 


stimuli  which  are  inefficacious  (by  default  or  by  excess)  when  they  are 
made  use  of  on  motor  nerves.  Hence  neurons  exist  whose  specific 
function  it  is  to  produce  inhibition.  It  is  possible  that  the  same  neuron 
may  produce  inhibition  by  one  of  its  terminations  and  excitation  by 
another,  but  it  is  necessary  always  to  admit  the  existence  of  a  terminal 
specific  and  inhibitory  apparatus. 

Objection. — Some  observei's  (Scliiff,  Moleschott)  have  endeavoured  to  refer 
inliibition  to  a  phenomenon  of  ordinary  paralysis.  They  maintain  that  the 
stoppage  of  the  heart  by  stimulation  of  the  vagus  arises  simply  from  an  altera- 
tion of  the  motor  properties  of  the  fibres  of  this  nerve,  which  are  excited  in  special 
conditions,  and  hence  deprived  of  their  motor  power. 

Reply.     Different  proofs. — The  objection  falls  to  the  ground  through  the  fact, 


f\ 


f^       A-v 


^— 


E  =  60    secondea 


Ar:62  sec     / 


/'   \/'V\/^- 


E  =  30    secondes 


Ar^32  sec  /' ^ 


V/\/\/-vr\ 


,/V^X/\ 


vr.A,.A„     I 


V  A.j'vA,.^- 


E=2 


Fig.  107. — Cardio-inhibitory  effects  of  stimulation  of  the  vagus  in  the  turtle  (laboratory 

tracing). 

Witliin  the  limits  of  intensity  of  the  current  which  corresponds  to  an  optimum  excitation,  the 
duration  of  the  cardiac  arrest  is  sensibly  proportional  to  the  duration  of  the  excitation. 

The  interval  between  the  starting  of  excitation  and  that  of  arrest  (latent  period)  is  remarkably 
long,  more  than  the  duration  of  one  and,  sometimes,  of  several  pulsations. 

The  recommencement  of  contractions  of  the  heart  is  marked  by  one  or  more  contractions 
stronger  in  proportion  as  fhe  stopjjage  has  been  longer.  There  is  a  tendency  to  compensation 
with  the  aim  of  maintaining  constancy  in  the  work  of  the  heart  as  a  whole.  Inhibition  does  not 
act  by  destroying,  but  by  suspending  and  preserving  the  stimulation  brought  to  the  muscle 
by  its  motor  nerves. 


which  may  be  easily  proved,  that  the  stimulus  required  in  order  to  ensure  stop 
page  by  exciting  the  vagus  has  the  same  qualities  as  that  which  is  recj[uired  to 
call  into  action  the  accelerator  nerves  of  the  heart. 

Excitation  in  parallel  series. — A  very  convincing  aspect  may  be  given  to  this 
demonstration  by  making  the  ordinary  conditions  of  stimulation  (intensity, 
frequency,  etc.)  vary  in  a  graduated  series.  In  such  a  case  the  response  of  the 
motor  nerve  goes  through  a  series  of  phases  characterized  by  a  minimum,  an 
oiitimum  and  a  pessimiun,  indicating  that  the  excitation  is  successively  ineffi- 
cacious by  default,  then  efficacious,  and  finally  once  again  inefficacious  by  excess. 
But  this  is  precisely  what  is  observed  with  inhibitory  nerves,  j'et  with  this  differ- 


232  SYSTEMATIC  FUNCTIONS 

ence  corresponding  to  their  function,  that  the  response  is  not  movement,  but 
tlie  stojDpage  of  inovement  (Morat). 

Effects  of  fatigue. — Another  proof  of  the  same  kind  :  in  tlie  prolonged  stimu- 
lation of  the  motor-  nerve,  fatigue  of  the  apparatus,  which  ensues  after  a  certain 
time,  hinders  the  continuation  of  the  movement.  In  prolonged  excitation  of  an 
inhibitory  nerve,  fatigue  also  occurs,  but  with  this  difference,  that  it  hinders  the 
contimtation  of  the  stoppage  and  consequently  causes  the  reappearance  of  move- 
ment. Hence  the  stoppage  is  indeed  in  this  case  a  result  of  the  activity  of  the 
stimulated  nerve,  and  not  a  consequence  of  its  alteration  ;  for  if  activity  involves 
fatigue,  alteration,  that  is  to  say  destruction,  does  not  involve  it. 

Invariability  of  the  effects  of  the  excitation. — If  inhibition  was  connected  with 
certain  variable  conditions  according  to  the  nature  of  the  nerve,  it  would  be 
possible  to  obtain  inhibition,  in  certain  cases,  by  stimulating  the  accelerators  of 
the  heart  and,  conversely,  acceleration  by  exciting  the  pneumogastric.  But 
this  is  not  the  case.  The  trunk  of  the  tenth  pair  contains,  it  is  trvie,  accelerating 
fibres,  the  existence  of  which  can  be  demonstrated,  not  by  modifying  the  nature 
of  the  stimulus,  but  by  paralysing  the  inhibitory  fibres  with  belladonna  ;  but  its 
origins  do  not  contain  any  of  these  fibres,  and  the  invariable  result  of  the  stimu- 
lation of  these  origins  is  slowing  or  stoppage  of  the  heart  (Heidenhain). 

Another  objection. — By  applying  the  stimulus  to  the  white  matter  of  the 
brain,  sometimes  motor  effects,  sometimes  inhibitory  effects  ensue,  yet  never- 
theless no  distinct  fasciculation  can  be  discovered  in  this  substance  to  which 
inhibition  rather  than  motor  activity  can  be  attributed  ;  hence  it  has  been 
sujoposed  that,  as  regards  this  organ  at  least,  the  same  fibres  are,  according 
to  circumstances,  motor  and  inhibitory. 

Reply. — In  the  same  organ  (the  brain)  the  manifestations  of  sensation  and 
motion  are  in  many  points  inextricably  mixed.  But  we  do  not  hence  conclude 
that  they  belong  indifferently  to  the  same  elements,  but  to  distinct  elements 
which  are  confused  together.  And  this  reasoning  holds  for  inhibition  as  it  holds 
for  the  other  specific  functions  which  are  discharged  by  the  functional  activity 
of  the  nervous  system.  It  is  sufficient  that  the  proof  of  this  functional  distinc- 
tion has  been  established  in  certain  typical  cases  in  which  analysis  is  possible. 
The  cases  which  are  refractory  to  analysis  ought  not  to  be  appealed  to  as  in- 
validating this  proof,  or  as  proving  the  existence  of  properties  of  nerve  elements 
which  are  incompatible  with  those  conferred  from  other  sources. 

Field  of  inhibition. — The  examples  of  avithentic  and  invariable  inhibitory 
nerves  are  continually  increasing.  They  exist  for  the  vessels  as  well  as  for  the 
heart  ;    for  the  intestine  as  well  as  for  the  circulatory  apparatus. 

Inhibition  is  rejDresented  in  all  the  partial  systems  which  make  ujj  the  nervous 
system  ;  and  it  everywhere  obeys  the  same  law  ;  it  is  governed  by  sjDccial  nerves 
in  the  partial  nervous  systems. 

Specific  nature  of  the  relationships. — The  three  constituent  elements 
of  the  system  constructed  in  this  way  each  possesses  the  fundafnental  pro- 
perties of  the  nervous  element  (excitability  and  conductivity),  and  so  far 
are  not  distinguishable  the  one  from  the  other  ;  hut  they  have  each  a 
specific  nature  as  regards  the  connexions  which  they  contract  at  their  ex- 
tremities. The  one  enters  into  relationship  with  the  cardiac  muscle 
like  an  ordinary  nerve,  the  two  others  form  a  relation  with  the  grey 
ganglionic  matter,  and  these  relations,  which  cannot  be  defined  by 
anatomy,  are  clearly  different  for  each  of  them. 

Inhibition  is  an  internal  phenomenon  of  the  nervous  system. — Hence 


PRIMARY  SYSTEMATIZATIONS  233 

inhibition,  in  order  to  take  place  in  its  habitual  and  normal  conditions, 
requires  the  activity  of  a  nerve  which  has  special  relationships  with 
other  nerves,  and  without  this  activity  it  does  not  occur.  The  very 
curious  consequence  of  this  activity  of  the  nerve  is  the  repose  of  a 
muscle  (or  of  an  analogous  organ)  ;  but  this  muscular  repose  is  itself 
the  consequence  of  the  repose  imposed  on  its  motor  nerve.  It  is  on 
this  account  that  inhibition  is  called  an  internal  phenoynenon  of  the 
nervous  system.  The  still  unknown  mechanism  which  gives  origin  to 
it  is  perfected  in  the  grey  matter  wherever  the  latter  exists,  because 
the  phenomenon  of  inhibition  is  general,  and  is  met  with  in  all  func- 
tions and  in  each  of  their  degrees.  The  inhibitory  nerves  never  pass 
beyond  the  most  superficial  layer  of  this  grey  matter  ;  they  corre- 
spond to  what  was  formerly  known  as  the  intercentral  fibres  and  to  what 
are  now  called  elements  of  association,  elements  whose  two  extremities, 
initial  and  terminal,  are  embedded  in  nervous  grey  matter  and  have 
no  direct  contact  with  organs. 

The  grey  matter  in  the  nervous  system  presents  superposed 
layers  ;  hence  it  has  a  superior  and  inferior  limit.  As  regards  the 
muscles  of  the  skeleton,  this  inferior  limit  is  in  the  grey  medullary 
axis  ;  as  regards  the  muscles  and  other  visceral  organs,  it  is  in  the 
ganglia  of  the  chain  of  the  great  sympathetic.  If  our  scheme  of  in- 
hibition is  exact,  there  should  not  be  in  the  nerve  trunks  which  proceed 
from  the  spinal  cord  to  the  muscles  of  the  skeleton  any  inhibitory 
element.  Experiment  verifies  this  induction  ;  by  stimulating  an 
extra-medullary  motor  nerve  of  a  skeletal  muscle,  nothing  but  its 
contraction  has  been  realized,  stoppage  of  its  movement  has  never 
occurred.  But  these  inhibitory  fibres  are  met  with  in  the  cerebral 
and  spinal  tracts.  They  are,  in  truth,  difficult  to  demonstrate  by 
stimulation,  because  they  are  mixed  with  the  fibres  which  give  rise  to 
movement,  and  there  is  no  means  of  separately  irritating  them  ;  but, 
nevertheless,  their  existence  has  been  proved. 

The  great  sympathetic  (to  which  the  pneimiogastric  is  united  by  the  majority 
of  its  elements)  affords,  on  the  other  hand,  on  account  of  the  dissemination  of 
its  branches  through  other  tissues,  an  exceptionally  easy  means  for  the  separate 
stimulation  of  its  tracts  of  different  fvmction  :  this  is  doubtless  the  reason  why 
the  phenomena  of  stoppage  have  been  recognized  in  it  before  being  susjoected 
in  the  remainder  of  the  nervous  system.  On  the  other  hand,  the  motor  neiu-ons 
which  proceed  from  its  ganglia  to  the  organs  of  visceral  movement  are  often 
embedded  in  the  tissue  of  the  latter,  and  rvm  so  short  a  course  that  inhibition 
appears  to  be  effected  in  these  very  organs  themselves  :  this  is  jDrecisely  what 
occurs  in  the  heart.  It  may  neverthless  be  shown  that  the  grey  matter  of  the 
ganglia  is  a  locality  in  which  the  inhibitory  elements  of  the  great  sympathetic 
terminate. 

Experiment. — In  a  rabbit  the  chain  of  the  great  sympathetic  is  exposed,  in 


234  SYSTEMATIC  FUNCTIONS 

front  and  behind  the  ganglia  of  the  base  of  the  neck  ;  an  excitation  made  pos- 
teriorly, that  is  to  say,  above  these  ganglia,  inhibits  the  vascular  muscles  of  the 
external  ear,  which  is  rendered  evident  by  an  intense  vaso-dilatation  of  this 
organ  (Dastre  and  Morat).  Excitation  applied  anteriorly,  that  is  to  say,  below 
these  ganglia,  contracts  these  vascular  muscles,  as  is  proved  by  the  pallor  of 
the  same  organ.  The  site  of  the  inhibition  is  clearly  in  the  ganglia,  which  thus 
indicates  the  starting  point  from  which  this  inversion  of  effects  occurs. 

3.  Excitation  and  inhibition. — In  short,  the  inhibitory  neuron  re- 
ceives normally  by  its  dendrites,  or  artificially  during  its  course,  a 
stimulus  which  has  no  need  of  any  special  quality  in  order  to  cause  it 
to  fulfil  its  function.  This  stimulus  traverses  the  neuron  and  proceeds 
to  terminal  arborizations.  When  it  has  arrived  at  its  destination  it 
produces  that  special  effect  which  is  rendered  evident  by  the  repose, 
the  non-activity  of  the  motor  neuron  to  which  it  is  distributed.  This 
effect  in  different  intensities  is  invariably  the  same  as  regards  the 
neuro-motor  apparatus  thus  brought  into  relationship  with  the  excited 
elements.  But  the  terminal  connexions  of  the  inhibitory  neuron  are 
multiple.  While  certain  of  them  are  in  inhibitory  relationship  with 
given  neuro-muscular  elements,  others  may  be  in  relationship  of  ex- 
citation with  other  elements,  in  such  a  manner  that  stimulation  has  a 
double  effect,  partly  inhibitory,  partly  motor,  no  longer  successive  but 
simultaneous,  and  it  is  in  this  sense  only  that  it  can  be  said  that  the 
same  fibre  is  both  motor  and  inhibitory.  This  double  relation  has  a 
definite  object  :  when,  for  example,  two  muscles  are  antagonistic  one 
to  the  other,  and  when  a  movement  should  ensue  in  one  of  them,  there 
is  an  economy  of  force  if,  by  the  aid  of  the  nervous  system,  the  one 
can  be  relaxed  while  the  other  contracts. 

Thanks  to  the  multiplicity  and  the  variety  of  its  terminal  polar 
connexions,  one  and  the  same  fibre  7nay  he  excito-motor  in  function  for 
certain  of  the  elements  with  which  it  enters  into  relationship,  and  in- 
hibitory for  certain  other  of  these  elements.  But  experiment  shows 
that  these  relationships  are  not  capable  of  being  inverted. 

Reflex  action  and  inhibition  combined  in  the  same  Cycle. — The 
reflex  action  and  the  inhibitory  action  may  thus  co-exist  simidtaneously 
in  a  mass  of  grey  matter  ;  they  represent  as  a  whole  but  one  aspect 
of  the  numerous  functions  of  this  matter.  On  the  other  hand,  these 
two  actions  are  also  associated  in  succession  ;  for  example,  a  stimula- 
tion of  the  skin  is  transmitted  to  the  spinal  cord  by  its  sensory  nerves, 
is  thence  reflected  to  an  inhibitory  nerve,  such  as  the  vagus,  by  it 
conveyed  to  the  ganglia  of  the  heart  and  causes  stoppage  of  this  organ  : 
this  is  one  of  the  ways  in  which  cardiac  syncope  is  brought  about. 
Again,  this  stimulus  may  be  reflected  in  the  form  of  an  inhibition  to 
some  gland  whose  secretion  it  stops,  as  Gley  has  observed  for  the  sub- 


PRIMARY  SYSTEMATIZATIONS  235 

maxillary  gland.  Yet  again,  it  may  be  reflected  so  as  to  exert  an 
inhibitory  influence  on  some  muscle  of  the  skeleton  whose  commencing 
contraction  it  arrests,  as  Beaunis  has  observed.  In  all  these  examples 
it  passes  through  a  chain  of  neurons,  in  the  course  of  which  at  one  of 
the  halting  places  it  changes  its  character,  that  is  to  say,  from  being 
a  promoter  of  contraction  it  becomes  an  obstacle  to  the  same.  It  is 
not  always  easy  to  clearly  ascertain  the  situation  of  this  remarkable 
halting-place.  One  thing  is  certain,  however,  that  it  is  neither  wholly 
at  the  commencement  nor  wholly  at  the  end  of  the  cycle,  but  some- 
where in  its  course,  in  what  is  called  the  centres  of  the  nervous  system. 

The  impulse,  whicli  starts  from  a  limited  sensory  area  (for  instance,  from  a 
l^ortion  of  the  cutaneous  svirface),  in  order  to  proceed  to  an  equally  defined  motor 
organ  (for  instance,  the  heart),  passes  through  a  system  of  neurons  which  are  at 
first  divergent  and  afterwards  convergent,  impressing  on  it  numerous  and  distinct 
modifications,  some  parallel  others  successive.  The  direction  of  the  reactional 
■effect  expresses  the  resultant  of  the  numerous  conflicts  which  take  place  in  this 
aggregate.  It  is  the  intrinsic  complexity  of  this  system  which  renders  it  able 
to  react  in  a  varied  manner  as  regards  stimuli  which  seem  to  be  identical.  It  is 
certain  that  it  is  not  at  times  consistent  with  itself.  It  is  this  complexus  of  neu- 
rons which  many,  for  simplicity's  sake,  have  endeavoured  to  reduce  to  a  single 
element,  possessing  now  the  "  motor  property,"  now  the  "  inhibitory  property." 
The  attempt  is  praiseworthy,  but  it  is  opposed  to  the  facts  both  of  anatomy 
and  of  experiment. 

Inhibition,  dynamogeny. — The  study  of  the  nervous  system  leads  us  to  sus- 
pect in  it  the  existence,  not  only  of  functions  which  are  clearly  defined,  such  as 
reflex  action  and  inhibition,  but  also  of  others  which  are  more  obscure,  the  neces- 
sity of  which  we  imderstand  without  being  able  to  ascertain  their  determination. 
Stimulations  of  a  sensory  nerve  often  produces  very  diverse  effects  in  the  grey 
matter  which  receives  the  stimulus.  Sometimes  it  suppresses  certain  of  the 
communications  which  exist  between  the  elements  of  the  latter  and  diminishes 
the  motor  effects  over  which  this  grey  matter  presides  :  this  result  is  due  to 
inhibition.  Sometimes,  on  the  contrary,  these  communications  seem  to  be  re- 
inforced and  extended,  and  the  flow  of  impulses  increases  as  it  passes  through 
the  grey  matter  :  this  is  the  phenomenon  to  which  Brown-Sequard  gave  the 
name  of  dynamogeny.  According  to  these  facts,  we  learn  that  the  grey  matter 
possesses  a  directive  function,  or  one  of  orientation,  no  longer  general  like  that 
determining  the  total  current,  which  causes  the  impulses  to  move  forward  in 
proceeding  from  the  sensory  organs  to  those  executive  of  functions,  but  a  parti- 
cular, localized  and  contingent  function,  which  in  the  complicated  network 
formed  by  the  nervous  paths  makes  them  take  such  and  such  a  branch  road 
rather  than  any  other.  This  is  the  function  which,  in  the  German  langtiage, 
Exner  has  described  by  the  word  "  Bahnung,''  for  which  it  would  be  difficult  to 
find  a  suitable  equivalent  ;  but  if  the  creation  of  a  word  be  permissible,  perhaps 
the  expression  "  viatility  "  may  serve  to  indicate  the  idea  of  the  facilitation  of 
transmission  brought  about  by  this  function. 

4.  Mechanism  of  inhibition. — This  is  totally  unknown  to  us,  as  is 
also  that  of  reflex  action.  This  latter  is,  however,  more  easy  of  com- 
prehension in  the  sense  that  it  demonstrates  to  us  the  communication 
of  the  movement  of  one  body  to  another  ;   while  in  inhibition  it  is  the 


236  SYSTEMATIC  FUNCTIONS 

movement  of  a  body  which  is  made  use  of  to  render  another  body- 
immobile.  Doubtless  physical  science,  both  molar  and  molecular,, 
furnishes  examples  of  effects  of  this  nature  ;  but,  so  long  as  we  are 
unable  to  precisely  define  the  nature  of  the  movement  which  is  thus- 
produced  and  arrested,  every  theoretical  attempt  at  explanation  will 
have  merely  the  value  of  a  comparison.  These  comparisons  show  us 
that  the  phenomenon  may  be  included  in  the  category  of  explicable 
facts,  but  the  explanation  itself  is  wanting. 

5.  Secondary  effects  of  inhibitory  excitation. — The  stoppage  of  the 
movement  of  organs  is  the  most  striking  fact  of  inhibitory  activity, 
but  it  is  not  the  only  one.  The  following  fact  must  be  taken  into  con- 
sideration. If  the  movements  of  the  heart  are  recorded  and  the  vagus 
stimulated,  the  tracing  indicates  suspension  of  its  beats  ;  then  these 
latter  recur  after  the  excitation  ;  but  this  remarkable  fact  is  observed 
that,  during  this  recurrence  of  the  beats,  they  are  at  first  stronger  or 
more  numerous  ;  to  such  an  extent,  indeed,  that  if  the  work  of  the 
heart  be  calculated  before  and  after  the  stimulation  (for  equal  periods 
of  time),  the  two  amounts  are  practically  equal.  The  same  observa- 
tion can  be  made  conversely  when  the  motor  nerves  of  the  heart  are 
stimulated  in  order  to  accelerate  its  action.  The  acceleration  which 
ensues  is  followed  by  a  compensatory  retardation  (Marey). 

As  regards  regular  functions,  such  as  that  of  the  heart,  nerve  stimu- 
lation, whether  it  be  provocative  or  inhibitory,  would  not  then  cause 
a  change  in  the  total  quantity  of  movement,  but  would  only  distribute 
it  in  a  different  manner  as  regards  time. 

It  may  be  asked  if,  as  regards  space,  the  stimulus  which  seems  tO' 
disappear  and  to  be  annihilated  in  the  grey  matter,  does  not  merely 
undergo  a  change  of  direction  for  a  certain  period. 

Inhibition  and  anabolism. — By  cataholism  is  understood  the  expenditure  of 
energy  of  the  tissues  (chiefly  of  tlie  muscular)  during  their  activity  ;  by  anabolism 
is  implied  the  reconstitution  of  potential  which  follows  this  activity  :  metabolism 
is  the  aggregation  of  these  operations.  The  catabolism  of  the  tissues  is  under 
the  dependence  of  the  nervous  system,  in  the  sense  that  the  tissues  do  not  become 
active  unless  this  system  intervenes  in  order  to  upset  the  imstable  equilibrivmi 
in  which  they  are  found  in  the  so-called  state  of  repose.  For  the  sake  of  uni- 
formit}^  it  has  been  thought  that  anabolism  should  be  ecjually  under  the  depend- 
ence of  the  nervous  system.  Two  kinds  of  nerves  ai'e  distributed  to  the  organs  : 
some,  strictly  motor,  are  catabolic  (provoking  expenditure)  ;  the  others,  in- 
hibitory, should  be  anabolic  nerves  (working  for  reconstitution).  This  con- 
ception is  seductive,  but  if  examined  more  closely,  it  will  be  obvious  that  it  is 
in  no  sense  justified.  Let  us  take  a  particular  example,  that  of  the  heart,  and 
let  us  see  how  its  nerves,  the  activity  of  which  differs,  influence  its  energetic 
jarocesses. 

(a)  Inhibition  and  heat. — If  the  inhibitory  nerve  of  tlie  heart  be  stimulated, 
the  temperature  of  tliis  organ  falls.     It  again  rises  when  its  movements  recom- 


PRIMARY  SYSTEMATIZATIONS  237 

mence.  Must  it  therefore  be  concluded  that,  during  stimulation  of  the  vagus 
.and  the  repose  which  results,  the  heart  absorbs  heat,  which  it  afterwards  gives 
•out  ?  Certainly  not  ;  the  explanation  of  the  phenomenon  is  far  more  simple. 
The  stimulation  of  the  vagus,  by  depriving  the  heart  of  the  impulses  wliich  it 
normally  receives,  causes  it  to  economize  its  combustible  reserves,  restricts  its 
•expenditvu-e  of  energy,  whence  the  relative  lowering  of  its  temperature.  There 
is  a  diminution  of  the  pre-existing  energetic  phenomenon  ;  there  is  no  inversion 
■of  this  phenomenon. 

(b)  Inhibition  and  the  electric  current. — The  heart  (wlien  it  is  incised)  presents, 
like  other  muscles,  a  ciu-rent  of  repose.  At  the  moment  of  its  contraction,  this 
current  of  repose  undergoes  a  negative  variation.  If  the  vagus  is  then  excited, 
a  'positive  variation  of  this  cm-rent  of  repose  is  observed  (Gaskell).  How  is  tliis 
phenomenon  to  be  interpreted  ?  Is  it  the  indication  of  a  reversal  of  the  ener- 
getic phenomena,  which  from  being  analytic  would  in  the  heart  become  sjti- 
thetic  ?     This  is  certainly  not  the  case. 

Here  again  the  explanation  is  much  simpler.  A  nuiscle  in  a  state  of  tonic 
■contraction  fm-nishes  a  current  of  repose,  which  is  diminished  by  the  negative 
variation  corresponding  to  its  tonic  activity.  If  we  diminish  this  tone,  by  in- 
hibiting the  muscle,  the  current  of  repose  will  increase  ;  hence  the  apparently 
positive  variation  of  the  current  ot  repose.  If  we  increase  this  tone  by  stimula- 
tion of  the  motor  nerves,  then  the  negative  variation,  such  as  is  ordinarily 
•observed,  will  be  produced.  In  every  case,  when  the  polarities  are  reversed  in 
a  circuit  it  must  not  be  concluded,  simply  from  this  fact,  that  the  chemical  pheno- 
mena which  are  the  cause  of  it  have  changed  their  denomination  ;  only  one 
thing  is  certain,  namely,  that  the  current  has  changed  its  direction. 

Asymmetry  of  the  anabolic  and  catabolic  phases. — The  belief  that  the  positive 
A^ariation  of  the  current  is  connected  with  muscular  anabolism,  while  its  negative 
variation  is  connected  with  its  catabolism,  corresponds  to  the  other  conception 
that  these  two  processes,  the  one  destructive,  the  other  restorative  as  regards 
the  muscular  reserves,  are  at  the  same  time  sjinmetrical  and  opposed,  each  one 
•of  the  two  phases  representing  the  exactly  contrary  operation  of  the  preceding. 
But  here  again,  if  the  facts  are  more  closely  examined,  it  will  be  seen  that  they 
in  no  sense  justify  this  manner  of  regarding  the  c^uestion. 

The  only  tolerably  accurate  information  which  we  possess  concerning  muscular 
metabolisna  is  derived  from  the  study  of  exchanges  with  the  blood.  We  see 
that  the  blood  furnishes  glucose  and  oxygen  to  the  muscle,  while  the  muscle 
supjDlies  the  blood  with  carbonic  acid.  Limited  though  it  may  be,  yet  this  in- 
formation has  great  value  concerning  the  natvu-e  of  energy.  The  substance 
•(glucose)  which  j^asses  from  the  blood  to  the  muscle  (dm-ing  tlie  anabolic  phase) 
possesses  a  large  amount  of  energy  ;  while  that  (carbonic  acid)  which  is  delivered 
to  the  muscle  from  the  blood  during  the  catabolic  phase  is  almost  totally  de- 
prived of  energy.  This  proves  that,  from  the  energetic  jDoint  of  view,  the  ana- 
bolic phase,  strictly  speaking,  does  not  practically  exist  either  in  muscles  or  in 
any  of  the  animal  organs,  but  rather  in  the  vegetable,  which  by  its  chemical 
syntheses  accumulates  that  provision  of  energy  which  it  will  deliver  up  to  the 
animal.  A  proof  that  this  anabolism  is  of  such  a  nature  as  to  dispense  with  the 
nervous  system,  while  catabolism,  so  active  in  the  animal  as  compared  with  the 
vegetable,  is,  on  the  contrary,  under  the  dependence  of  this  system. 

Comparison  of  inhibition  with  neuro-motor  paralysis. — Wlietlier  it  is  a  ques- 
tion of  the  muscular  exchanges,  of  its  mechanical  work,  or  of  its  heat  given  off, 
■or  of  its  electrical  phenomena,  we  cannot  fail  to  be  struck  by  the  following  fact  : 
the  intervention  of  the  inhibitory  nerve  acts  in  the  same  way  as  if  section  of 
the  motor  nerve  of  the  muscle  in  question  had  been  performed.  It  suppresses 
in  the  muscle  the  impulses  which  it  received  from  the  centres  ;   it  seems,  indeed. 


238  SYSTEMATIC  FUNCTIONS 

that  it  does  still  more,  and  affects  it  throughout  its  extent  with  a  momentary 
incapacity  to  react,  placing  it  indeed  in  a  state  of  inactivity  which  we  know  tO' 
be  only  transitory,  but  which  is  equivalent,  so  long  as  it  lasts,  to  paralysis  ; 
whence  the  name  of  'paralysing  nerves  which  was  formerly  given  to  the  inhibitory 
nerves  or  to  those  of  arrest. 

The  paralysis,  of  which  it  is  here  a  c^uestion  (if  om-  comparison  is  exact),  is  not 
then  a  muscular  paralysis,  but  a  paralysis  of  the  motor  nerve.  It  is  by  affecting 
the  motor  nerve,  and  not  the  muscle  ivhich  follows  it,  that  the  inhibitory  nerve  effectSy 
at  the  least  expense  and  temporarily,  tlutt  special  paralysis  which  corresponds 
to  inhibition  and  which  is  characterized  by  the  fact  that  it  depends  on  the  activity 
of  a  special  nerve,  the  inhibitory  nerve. 

Lengthening  of  the  muscle. — Whether  we  either  interrupt  the  anatomical 
continuity  of  the  motor  nerve,  or  whether  we  suspend  its  tonic  activity  by  in- 
hibition, the  result  in  both  cases  will  be  the  lengthening,  not,  indeed,  active  but 
passive,  of  its  muscles,  which  thus  yield  to  the  exertions  of  the  antagonistic 
powers.  This  is  what  happens  in  the  vascular  apparatus  both  throvigh  section 
of  the  vaso-constrictors  and  excitation  of  the  vaso-dilators.  De  Varigny  has 
observed  in  the  invertebrata,  by  oj^erating  on  a  muscle  of  the  Stycopus  regaliSy 
that  stimulation  sometimes  causes  very  obvious  lengthening  of  this  muscle. 
The  explanation  of  this  lengthening  probably  lies  in  an  inhibitory  phenomenon 
of  this  natvire. 

Neuro- muscular  paralysis  and  anabolism. — Let  us  continue  om-  comj)arison. 
Let  a  muscle  be  taken  of  which  we  have  cut  the  motor  nerve  between  the  spinal 
cord  and  itself.  We  will  not  choose  the  heart,  because  this  muscle  carries  with 
it  its  portion  of  the  spinal  cord,  I  mean  its  ganglia,  and  many  other  muscles  of 
organic  life  resemble  it  in  this  respect  ;  but  the  skeletal  muscles  are  available  for 
this  experiment  of  enervation.  During  the  time  which  immediately  follows- 
section  of  the  motor  nerve,  that  is  to  say,  before  degenerative  jDrocesses  have 
commenced  in  the  nerve  and  muscle,  the  paralysis  of  these  two  organs  is  purely 
fvinctional.  Both  cease  to  receive  the  stimuli  which  are  normally  sent  to  them 
by  the  nervotxs  centres  ;  they  are  in  a  condition  of  enforced  repose.  The  cata- 
boUsm  which  depends  on  these  stimuli  ceases  in  them  on  this  account,  or,  at  all 
events,  is  very  much  redviced  ;  the  exchanges  are  diminished,  as  also  the  dis- 
engagement of  heat  ;  the  mechanical  work  is  nil  ;  but  anabolism  persists  in 
this  enervated  muscle,  just  as  in  normal  muscle.  If  a  proof  of  this  is  sought,  it 
is  only  necessary  to  excite  its  nerve  artificially  ;  the  muscle  will  then  supply^ 
even  to  exhaustion,  a  new  amount  of  energy  in  the  form  of  work  and  of  heat. 
In  order  that  it  may  recuperate,  it  will  suffice  to  leave  it  in  repose  for  a  certain 
time.  Then,  once  again,  the  stimulus  may  be  applied,  and  so  on.  If  the  muscle 
has  remained  in  connexion  with  its  vessels,  matters  will  take  place  as  just  de- 
scribed. If  the  muscle  is  detached  from  the  animal,  the  exhaustion  at  the  end 
of  a  certain  time  will  be  definite,  because  then  the  muscular  element  works  on 
a  provision  which  is  no  longer  renewable. 

Reciprocal  bond  of  union  between  anabolism  and  catabolism. — The  cata- 
bolism  of  tlie  tissues  is  directly  dependent  upon  the  ner\-ous  system  ;  anabolism 
is  not  directly  dependent  upon  it  :  this  is  clearly  obvious  from  the  preceding 
experiments.  There  are,  nevertheless,  between  anabolism  and  catabolism  re- 
ciprocal bonds  of  union  which  ordinary  observations  render  evident.  When  an 
organ  is  entirely  and  definitively  deprived  of  stimuli,  far  from  anabolism  being 
maintained  at  its  highest  level,  the  organ,  on  the  contrary,  atrophies  for  want 
of  exercise.  It  is  true  that,  if  this  organ  is  excessively  stimulated,  it  may  also 
be  compromised  by  this  over-activity.  The  condition  which  must  be  fulfilled 
is  that  it  receives  stimuli  in  svifficient  quantity,  without  excess  and  without 
default.     Life  is  an  equilibrium,  but  this  ecj[uilibrium  is  not  static,  it  is,  on  the 


PRIMARY  SYSTEMATIZATIONS  23& 

contrary,  mobile  ;  it  is  based  on  a  cuiTent  acconnt,  of  which  the  receipts  and 
expenses  regularly  balance  ;  the  irregularity  of  this  account,  however  indviced,. 
is  a  cause  of  destruction  for  the  living  organization.  The  nervous  system  inter- 
venes every  moment  to  hinder  it  from  ceasing  or  from  exaggerating  its  rapidity. 
As  this  cvirrent  in  the  animal  organism  may  be  compared  to  a  waterfall,  it  hence 
follows  that  every  effort  of  the  nervous  system  is  limited  to  opening  the  flood- 
gates when  the  ciirrent  is  slow, — this  is  excitation  ;  and  to  closing  them  when 
it  rvms  too  fast,  this  is  inhibition. 

C.  CONSERVATION  OF  THE  STIMULUS.  NERVOUS  CIRCULATION 
It  is  clearly  obvious  that  the  impulses  are  preserved  in  the  nervous 
system  ;  we  see  them,  indeed,  ceaselessly  streaming  in  upon  us  by  the 
paths  of  the  senses  without  muscular  movement  immediately  following  ; 
and,  on  the  other  hand,  this  movement  may  arise  in  us  without  external 
provocation,  that  is  to  say,  long  after  the  provocation  has  taken  place. 
There  is  a  bond  of  union  in  time  between  present  motor  action  and  past 
sensory  excitations.  How  can  this  bond  of  union  be  explained  ?  How 
is  it  possible  to  comprehend  that  the  impulse  which  had  no  immediate 
effect,  and  which  seemed  to  be  lost  and  destroyed  in  the  nervous  paths, 
can,  nevertheless,  at  a  given  moment  reappear  with  its  primitive 
intensity  ?     How  is  this  hiatus  filled  up  ? 

1.  Circulation  of  the  excitation. — The  condition  of  excitation,  with 
the  consequences  which  it  induces  in  the  nervous  system  (conscious 
or  unconscious  sensation,  voluntary  or  involuntary  movement),  is 
governed  by  an  internal  movement  which  is  propagated  along  the 
nerves  at  a  definite  rate.  In  spite  of  the  retardations  or  temporary 
stoppages  which  it  experiences,  this  molecular  movement,  which  follows 
a  definite  direction,  will  discharge  itself  in  the  muscular  tissue,  if  there 
is  no  special  arrangement  by  which  it  can  be  retained  in  the  nervous 
system.  Excitation,  such  as  we  conceive  it  from  the  analytical  study 
of  the  nerve  elements,  does  not  imply  a  stationary  condition.  Hardly 
entered  into  a  cycle,  the  impulse  traverses  it  throughout  its  length, 
as  the  reflex  act  clearly  proves.  Arrived  at  its  termination,  it  has 
but  one  means  of  remaining  in  it,  namely,  to  reappear  by  a  device,  by 
penetrating  once  again  into  its  original  paths.  In  a  word,  it  is  only 
preserved  because  it  circidates  in  this  cycle,  and  inasmuch  as  it  circulates 
in  it.  How  is  this  circulation  carried  out,  and  what  are  the  anatomical 
conditions  which  render  it  possible  ? 

2.  Automatic  excitation. — In  numerous  cases  the  reflex  act  shows 
us  how  this  automatic  and  in  some  measure  indefinite  renewal  of  the 
excitation  is  effected.  In  the  mental  conception  of  this  act  there 
occurs  the  predominant  idea  of  a  strict  dependence  of  movement  upon 
sensation  (conscious  or  unconscious)  ;  but  this  idea  expresses  only  a 
portion  of  the  truth.     This  dependence  is  reciprocal,  in  the  sense  that, 


•240  SYSTEMATIC  FUNCTIONS 

if  muscular  movement  in  it  depends  on  a  sensory  excitation,  this  latter 
in  its  turn  depends  on  muscular  movement  ;  this  is  at  least  what  is 
easily  seen  in  a  large  number  of  functional  actions  of  a  simple  and 
regular  order,  such  as  those  which  maintain  the  so-called  functions  of 
nutrition  (movement  of  blood  in  the  vessels,  or  of  air  in  the  lungs, 
etc.). 

If  this  reciprocity,  this  automatism,  escapes  us  at  the  first  glance, 
it  is  because,  in  endeavouring  to  make  an  analysis  we  have  broken  it 
in  order  to  have  a  clearer  conception  of  the  internal  or  cejitral  bond 
which  connects  movement  and  sensation.  In  our  own  experiments 
we  ourselves  furnish  the  sensory  excitation,  in  order  to  be  sure  of  its 
provision,  and  we  receive  the  muscular  movement  in  a  myographic 
apparatus  the  better  to  observe  and  study  it.  But  this  system,  open 
to  the  exterior,  is,  we  repeat,  artificial  ;  in  any  case,  as  regards  things 
as  they  are,  it  is  far  from  being  the  rule.  An  external  tie,  peripheral, 
thus  connects,  in  its  turn,  sensation  to  movement  and  makes  it  to 
depend  upon  it.  The  cyclic  system,  once  primed,  continues  to  act 
functionally  by  itself.  Its  losses  through  excitation  are  minute,  its 
expenditure  of  energy  is  extremely  feeble  and  is  compensated  by  the 
exchanges  effected  with  the  blood  circulating  in  its  vessels. 

Superposed  reflex  arcs. — The^'nervous  system  is  formed  of  two  tiers  or  two 
superposed  systems,  which,  placed  one  above  the  other,  rejaeat  the  same  more 
or  less  complicated  scheme  ;  that,  namely,  of  an  arc  with  two  branches,  repre- 
senting a  double  canalization,  permeable  in  the  oi:)posite  direction  to  the 
impulses. 

(a)  Inferior  Arc. — The  inferior  system  is  formed  by  the  roots  of  the  nervous 
system  ;  these  are  elements  which  branch  out  from  the  grey  matter  of  the  sjoinal 
cord  and  the  ganglia  to  the  sensory  organs  and  those  of  movement.  This  prim- 
ary system  is  fundamental  ; .  it  is  the  compulsory  route  followed  by  the  exchanges 
which  (from  the  nervous  point  of  view)  take  place  between  us  and  the  external 
medium  ;  it  may  be  sufficient  in  itself  and  be  functionally  active,  as  alone  happens 
in  reflex  acts  properly  so  called  ;  it  is  even  capable  of  jDreserving  the  impulse  in 
itself  by  a  kind  of  neuro-muscular  circulation,  as  has  just  been  described. 

(b)  Sujjerior  Arc.^The  superior  system  is  fed  (as  regards  stimulation)  by  the 
preceding  ;  it  j^rolongs  it  into  the  interior  of  om*  bodies,  and  complicates  it  extra- 
ordinarily in  doing  so.  The  most  ordinary  observation  teaches  us  that  its  capa- 
city for  stimulation  is  almost  infinite.  It  represents,  as  regards  stimulation,  a 
reservoir  which  is  almost  inexhaustible.  It  also  stores  excitations  internally, 
and  this  conservation  is  the  first  condition  of  the  continuity  of  the  j^sychical  life 
(conscious  or  unconscious),  and  especially  of  the  memory.  We  know  that  this 
psychical  life  can  continue,  and  even  be  very  intense,  aj^art  from  every  external 
stimulus  and  from  every  reaction  against  the  external  world  ;  it  is,  therefore, 
concentrated  in  the  sviperior  parts  of  the  nervous  system,  chiefly  in  the  brain. 

Their  independent  functional  activity. — Clearly  the  sujaerior  system,  both  as 
a  whole  and  its  i^arts,  is  capable  of  isolation  like  the  inferior  ;  which  means  that, 
having  received  from  this  last  a  certain  provision  of  impulses,  it  lays  them  up  in 
itself  before  surrendering  them  to  it. 

The  mechanism  of  this  conservation  is  in  i^rinciple  the  same  as  that  which  we 


PRIMARY  SYSTEMATIZATIONS 


241 


have  seen  in  operation  in  the  inferior  system  ;  it  is  effected  by  an  automatism 
in  virtue  of  wliich  the  impulse,  after  having  traversed  its  jDatiis,  retui-ns  once 
again  to  them  by  a  sort  of  continuous  circulation.  Indeed,  anatomy  shows  us 
here,  again,  the  existence  of  a  genuine  closed  circuit,  instead  of  the  open  arc  which 
is  generally  accepted. 

Their  cyclic  form. — The  brain  and  the  spinal  cord  are  formed,  as  is  well  kno\^Ti, 
of  white  tracts  and  of  gi'ey  masses.  The  white  tracts 
are  composed  of  fibres  whose  direction  is  opposed, 
some  ascending,  others  descending,  the  fii'st  called 
sensory,  the  second  motor,  by  analogy -Rdth  the  functions 
of  the  medullary  root.  These  fibres,  which  are  inde- 
pendent and  isolated  throughout  their  course,  come  into 
relation  with  each  other  in  those  localities  wliich  are 
occupied  by  the  gi'ey  matter.  This  relation  has  been 
clearly  established  in  the  cerebral  cortex  between  their 
superior  extremities,  and  physiology  makes  use  of  it  in 
order  to  explain  the  i^assage  of  the  impulse  from  the  first 
to  the  second  ;  btxt  this  is  not  all  :  a  connexion  of  the 
same  natiire  has  been  proved  to  exist  between  their 
inferior  extremities.  The  circuit  postulated  in  order  to 
explain  the  conservation  of  the  impulse  has,  anatomicallj^, 
a  real  existence. 

Inferior  closure  of  the  circuit. — The  impulse,  we  say, 
is  communicated  from  the  ascending  to  the  descending 
fibres  (from  the  sensory  to  the  motor  fibres)  ;  this  com- 
munication is  obvious  in  the  cerebral  cortex  ;  but  fibres 
also  pass  from  descending  to  ascending  tracts  ;  this 
communication  is  recognizable  in  certain  sensory  organs, 
especially  in  the  retina,  the  olfactory  bulb,  the  nuclei 
of  the  acoustic  nerve.  The  optic  nerve  is  not  made  up 
solely  of  ascending  fibres  (centrii^etal),  but  it  also  con- 
tains descending  fibres  (centrifugal),  whose  terminal 
ramifications  are  exhausted  in  the  thickness  of  the 
retina.  The  impulse  which  the  ascending  fibres  have 
once  carried  to  the  brain  is  collected  by  the  descending 
fibres,  near  its  point  of  departure,  and,  by  the  connexions 
that  these  fibres  have  with  the  ascending  fibres  of  the 
optic  nerve,  it  is  once  again  carried  into  its  first  direction. 
There  is  a  periodical  and  automatic  renewal  of  the  im- 
jDulse. 

In  the  olfactory  bullr  the  same  arrangement  holds 
good,  but  with  the  interesting  detail  that  here  the 
arborizations  are  distinctly  seen,  those,  namely,  which 
collect  the  descending  impulse  in  order  to  keep  it  in 
the  circuit.  The  mitral  cells  of  the  olfactory  lobe  pre- 
sent, indeed,  in  addition  to  their  axon,  which  is  directed 
towards  the  brain,  two  kinds  of  prolongations. 

Some  of  them,  vertical  in  direction,  receive  the  external  stimulus  transmitted 
by  the  primary  olfactory  neuron  ;  others,  extending  laterally,  are  connected 
with  the  centrifugal  fibres  of  the  olfactory  lobe  (Van  Gehuchten).  It  is  these 
which  assiu-e  the  cu'culation  of  the  impulses  in  the  system. 

The  demonstrative  value  of  these  examples  lies  in  the  fact  that,  in  the 
extremity  of  the  centrifugal  descending  fibres  the  impulse  has  no  possible  con- 
nexion with  the  organs  of  movement ;  we  cannot  then  suppose,  considering  the 
known  properties  of  nerve  elements,  that  it  can  have  any  other  possible  destina- 

P.  R 


Fig.     108.— Peripheral 

reflection  of  impulses. 

a,  olfactory  cell  trans- 
mitting the  impulse  to 
the  interior  of  a  glomer- 
ulus ;  b,  mitral- cell  of  the 
olfactory  bulb  collecting 
this  impulse  by  a  special 
protoplasmic  prolonga- 
tion forwarding  it  to  the 
brain  ;  c,  axis-cylinder 
terminations  of  a  neuron 
bringing  back  the  im- 
pulse from  the  brain  to 
the  same  mitral  cell  b, 
which  collects  it  by  a 
distinct  protoplasmic 

prolongation  ;  d,  associa- 
tioning  cell. 

The  current  of  im- 
pulses proceeds  in  the 
direction  of  the  arrows. 
From  a  to  6  the  stimula- 
tion from  the  exterior 
penetrates  to  the  interior 
of  the  nervous  system. 
From  c  to  b  the  impulse 
circulates  in  a  cychc  sys- 
tem. 


242  SYSTEMATIC  FUNCTIONS 

tion  than  to  re-ascend  towards  the  brain.  The  cycle  is  thus  completed  without 
the  interposition  of  foreign  elements.  The  circulation  here  is  no  longer  neuro- 
mviscular  ;  it  is  internal  to  the  nervous  system  itself  ;  it  is  a  genuine  nerve 
circulation. 

Absence  of  Experimental  Proof. — Our  experimental  methods,  it  must  be 
admitted,  do  not  permit  us  to  observe  this  phenomenon  of  nerve  circulation  in 
actu.  Nervous  activity,  indeed,  is  not  discernible  in  itself,  and  the  only  avail- 
able evidence  of  its  existence  that  we  joossess  is  muscular  movement.  But,  on 
the  other  hand,  the  contrary  supposition,  that  the  impulse  ne\-er  passes  from 
the  descending  to  the  ascending  fibres  (a  supposition  which  lies  at  the  foundation 
of  all  the  actual  theories  of  nerve  function)  is  not  confirmed  by  an^•  experimental 
fact  which  proves  this  impossibility.  That  the  cerebral  refiex  arc  exists,  is  uni- 
versally allowed  ;  is  it  open  or  closed  at  its  inferior  extremities  ?  Experiment 
is  silent  on  this  point.  But  if  we  reflect  that  anatomy  shows  us  at  its  inferior 
extremity,  between  its  paths,  connexions  altogether  similar  (except  that  the 
relationships  are  inverted)  to  those  which  exist  at  its  summit,  the  hypothesis 
that  by  these  connexions  a  transmission  of  the  impulse  from  the  one  to  the 
other  is  rendered  possible,  as  in  the  brain,  is  certainly  jDlausible  and  niay  be 
maintained. 

D.     CLASSIFICATION    OF    NERVES 

A  methodical  and  analytical  classification  of  the  nerves  according 
to  their  functions  implies  a  knowledge  of  these  functions  which,  at 
the  present  time,  we  are  far  from  possessing.  However,  in  projjortion 
as  the  relations  which  the  nervous  system  forms  with  the  principal 
acts  of  the  organism  have  been  comprehended  an  effort  has  been  made 
to  distinguish  and  define  them,  by  imposing  upon  them  certain 
names.  The  result  is  that  a  nomenclature  has  been  constructed  whose 
terms  are  more  or  less  justifiable  and  the  sound  foundation  of  which 
it  is  necessary. to  discuss. 

Remark. — A  nerve  is  not  designated  according  to  the  nature  of  its 
intrinsic  activity  (which  we  imagine,  indeed,  to  be  uniform  in  all  the 
nerve  elements),  nor  even  from  the  nature  of  the  phenomenon  by 
which,  at  its  termination,  it  acts  on  the  elements  to  which  it  is  distri- 
buted (which  termination  may  also  vary  according  to  the  nature  of 
the  element  influenced,  but  is  entirely  unknown  as  regards  its  mechan- 
ism). All  nerves  without  exception,  all  the  species  of  nerves  which 
are  distinguished  the  one  from  the  other,  are  denominated  according 
to  the  nature  of  the  activity  ichich  they  arouse  in  the  elements  which  they 
immediately  or  mediately  govern,  according  to  circumstances.  These 
designations,  which  regard,  the  one  extrinsic  but  neighbouring 
function,  the  other  remote  function,  may  lead,  unless  care  is  taken, 
to  confusion  and  to  double  meaning. 

Here  are  the  principal  characters  which  may  be  recognized  in  accord- 
ance with  what  is  at  present  known. 

1.  Initial  and  terminal  neurons. — Sensory    and    motor    nerves. — In 


PRIMARY  SYSTEMATIZATIONS  243 

following  the  nerve  roots  in  the  direction  of  the  impulses  which  traverse 
them,  initial  neurons,  which  carry  the  impulse  from  without  to  the 
nervous  system  and  arouse  sensation  in  the  latter,  are  met  with  ;  these 
are  obviously  sensory  ;  at  the  other  extremity  terminal  neurons  are 
found.  A\hich  convey  the  impulse  to  the  muscles  from  the  nervous 
system  ;  these  are  clearly  motor.  Between  the  one  and  the  other 
intermediate  neurons  are  interposed,  forming  what  is  known  as  the 
central  nerve  mass,  as  opposed  to  the  roots  w^hich  have  just  been 
referred  to.  Conventionally,  this  mass  of  intermediate  or  associating 
neurons  is  divided  into  two  portions,  or  two  collections  of  fibres,  the 
One  still  called  sensory,  because  they  follow  the  roots  of  this  denomina- 
tion, the  others  motor  because  they  end  in  the  motor  roots.  But  a 
reserve  must  be  made  concerning  the  applicability  of  these  designa- 
tions, and  concerning  the  identification  which  would  be  effected  between 
them  and  their  homonyms  the  roots,  as  will  be  immediately  seen. 

(a)  Sensory  varieties. — The  sensory  nerves  (initial  neurons  of  the 
skin  and  of  the  sensorial  organs)  are  thus  named  from  the  altogether 
internal  phenomenon  of  sensation  to  which  they  give  rise  in  the  sensory 
or  sensorial  systems  of  which  they  form  the  gate  of  entry,  and  which 
are  situated  in  the  so-called  central  mass,  intermediate  between  them 
and  the  motor  roots.  In  this  category  of  sensory  nerves,  as  many 
subdivisions  and  species  as  there  are  distinct  senses  may  be  define^ ; 
each  is  definite,  both  as  regards  the  nature  of  the  excitation  of  the 
given  sense,  and  that  of  the  sensation  to  Avhicli  it  gives  rise,  that  is  to 
say,  of  the  systematic  function  which  comes  directly  after  it  (optic, 
acoustic,  tactile,  gustatory,  olfactory  nerves). 

(b)  Motor  varieties. — The  motor  nerves  (terminal  neurons)  are  also 
named  after  the  external  phenomenon  of  movement  which  they  initiate 
in  the  cells  with  which  they  come  in  contact  by  their  termination. 

Unlike  the  sensory  nerves,  which  ensure  the  accomplishment  of  a 
systematic  function,  they  give  rise  to  a  purely  cellular  function  (con- 
traction in  the  muscular  elements  ;  secretion  in  the  elements  of  the 
glands,  etc.).  They  are  divided  naturally  into  categories  correspond- 
ing to  these  functions  {motor  nerves  properly  so  called,  secretory  nerves, 
etc.). 

2.  Intermediate  neurons. — The  preceding  designations  are  both 
•comprehensible  and  legitimate  ;  the  problem  to  be  solved  is,  further, 
relatively  simple  when  it  is  a  question  of  the  two  varieties  of  the  pre- 
ceding nerves  ;  because,  being  placed  at  the  entrance  to  and  exit  from 
the  nervous  system,  they  permit  us  to  see  more  clearly  their  connexion 
with  the  exterior,  which  remains  our  criterion.  Very  great  difficulties 
arise  when  it  is  a  question  of  the  neurons  of  the  intermediate  mass 


244  SYSTEMATIC   FUNCTIONS 

and  when  we  endeavour  to  effect  a  classification  of  them  which  is  based 
on  their  functions.  Being  internal  to  the  nervous  system  itself,  with- 
out direct  connexion  with  the  peripheral  organs  for  the  reception  of 
the  stimulation  or  of  the  execution  of  movement,  we  are  deprived  of 
the  two  methods  which  have  served  us  above  for  choosing  and  justify- 
ing our  designations. 

They  receive  the  impulse  from  other  nerves  which  precede  them,  and 
they  restore  it  to  yet  other  nerves  which  follow  them.  Their  function 
is  thus  to  transmit  the  impulse  from  one  nerve  element  to  another. 
Either  as  regards  the  manner  in  which  they  receive  this  impulse,  or 
as  concerns  that  in  which  they  transmit  it,  there  is  no  doubt  that  they 
must  present  differences  amongst  themselves,  of  which  the  initial  and 
terminal  neurons  furnish  us  with  an  imperfect  example,  but  which 
are  certainly  still  more  obscure.  However,  positive  facts  teach  us 
that  this  transmission  may  have,  as  regards  the  activity  of  the  neurons, 
two  very  different  and  opposed  results. 

The  impulse  transmitted  from  one  neuron  to  another  may  have  the  effect  r 
(a)  of  elicitiyig  its  activity,  (b)  of  reducing  it  to  inactivity.  These  twO' 
effects  are  clearly  exclusive  the  one  of  the  other,  and  are  observed  in 
circumstances  peculiar  to  each  case. 

Exciting  and  inhibitory  neurons. — The  intermediate  neurons  may 
then  have,  as  regards  the  neurons  with  which  they  come  into  con- 
nexion, two  different  functions  by  which  they  may  be  divided  into  two 
distinct  classes.  Some  give  rise  to  activity,  and  elicit  the  function 
of  those  which  follow  them  :  they  may  be  called  excito-functional  or 
simply  exciting,  since  we  in  no  way  assume  the  function  which  they 
stimulate.  The  others  interdict  the  functional  manifestations  of  the 
nervous  paths  which  follow  them  :  they  may  be  called  inhibito- 
functional  or  simply  inhibitory,  in  opposition  to  the  preceding. 

The  activity,  whether  of  transmission  or  of  hindrance  to  the  trans- 
mission of  impulses  which  corresponds  to  the  most  general  function 
of  these  neurons,  is  capable  of  being  decomposed  into  a  certain  number 
of  secondary  functions,  comprising  the  modalities,  certainly  diverse, 
according  to  which  this  positive  or  negative  transmission  is  effected 
under  particular  circumstances. 

These  modalities  we  can  but  suppose  to  concern  the  direction,  the 
conflicts  and,  generally  speaking,  the  connexions  impressed  on  the 
impulses  in  the  complicated  systems  of  neurons  which  form  the  strictly 
nervous  portion  of  the  nervous  system. 

At  the  present  time  our  methods  of  analysis  do  not  supply  us  with 
any  means  of  directly  determining  the  actions  exerted  by  one  nervous 
element  on  another  nervous  element.     The  little  that  we  know  of  the^ 


PRIMARY  SYSTEMATIZATIONS  245 

latter  is  indirectly  furnished  to  us  by  the  ultimate  evidences  of  nerve 
action  (organs  of  the  movements  executive  of  functions). 

3.  Functional  systems  of  neurons. — Another  source  of  difficulty  in 
the  classification  of  nerve  species  lies  at  the  very  foundation  of  the 
subject  ;  I  mean,  it  arises  from  the  complexity  of  the  laws  Avhicli 
govern  the  organization  of  nerve  elements  in  hierarchically  superposed 
systems,  which  are,  each  in  turn,  constituent  portions  the  one  of  the 
other.  A  nomenclature  founded  on  dichotomic  distinctions,  analogous 
to  botancial  or  zoological  classifications,  is,  however,  insufficient  to 
give  an  idea  of  such  an  organization.  The  divisions  and  subdivisions 
of  the  nervous  functions,  when  they  are  exactly  known,  will  not  be 
spread  out  on  the  same  plane,  but  will  extend  in  many  directions. 

The  first  distinction  to  be  made  is  not  to  confound,  but,  on  the  con- 
trary, to  separate  the  functions  which  belong  to  elements  from  those 
which  belong  to  aggregations  ;  to  distinguish  cellular  functions  from 
systematic  functions.  Some  definite  examples  will  make  this  difference 
clear. 

Examples. — The  plirenic  nerve  is  the  motor  nerve  of  the  diaphragm.  For 
this  pvirpose  it  transmits  to  the  latter  an  imjDulse  in  order  to  bring  abovit  its  eon- 
traction  in  all  the  functions  in  wliich  this  muscle  participates.  As  is  the  case 
with  the  greater  mmiber  of  muscles,  these  functions  are  multiple.  As  regards 
the  diaphragm,  at  least  two  may  be  mentioned  :  the  ventilation  of  the  lung, 
and  the  swallowing  of  aliments.  The  diapliragm,  diu-ing  respiration,  draws  air 
into  the  chest  ;  in  swallowing,  it  draws  the  alimentary  bolus  into  the  oesophagus. 
In  the  first  case,  the  action  is  associated  with  that  of  a  certain  luunber  of  the 
thoracic  muscles  which  take  part  in  the  joerformance  of  respiration,  in  inspira- 
tion ;  in  the  second,  it  acts  together  with  the  buccal  muscles,  and  the  phaiyngeal 
and  the  oesoj)hageal  muscles,  which  jierform  the  act  of  deglutition.  These  mus- 
cular connexions  and  those  of  the  neurons  wliich  directly  control  these  nmscles 
are  effected  in  the  nervous  system,  namely,  in  that  portion  of  it  which  is  inter- 
mediate between  the  motor  and  sensory  nerves,  properly  so  called,  and  wliich 
is  formed  of  the  neurons  known  as  those  of  association.  In  order  to  perform  the 
function  of  deglutition,  the  phrenic  nerve  enters  into  a  complete  and  definite 
system  :  for  its  performance  of  respiration,  it  enters  into  another  ecj[ually  definite 
system.  It  is  not  the  phrenic  nerve  which  is  resi^iratory,  as  has  been  sometimes 
said,  but  rather  the  sj'Stem  to  which  it  belongs  at  the  instant  of  its  performing 
the  function  which  this  system  subserves. 

The  hypoglossal  nerve,  by  the  muscles  which  it  supplies,  maj'  also  take  part 
in  the  performance  of  several  different  functions  :  mastication,  deghitition, 
articulate  speech,  etc.  And  this  is  also  effected  by  the  connexions  which  it 
forms  with  other  nerves  suppljang  other  muscles  ;  associations  which,  according 
to  their  degree  of  importance  and  complexity,  are  effected  between  the  neiu'ons 
of  the  bulbar,  peduncular  or  cortical  region  of  the  nervous  system.  To  be 
acciu-ate,  the  reasoning  does  not  apply  to  the  hypoglossal,  a  bundle  of  neiu'ons 
taken  together,  but  to  each  component  neuron  of  this  nervous  bundle. 

The  same  remarks  would  apply  to  the  facial  and  other  motor  nerves.  These 
remarks  are  self-evident,  but  they  deserve  nevertheless  to  be  emphasized.  The 
expressions  respiratory  nerves,  nerves  of  phonation,  nerves  of  expression  and  such 


24G  SYSTEMATIC   FUNCTIONS 

like,  are  only  exact  when  it  is  understood  that  these  epitliets  are  transposed  fronn 
the  terminal  nerve,  to  wliich  they  are  customarily  ajaplied,  to  the  whole  which 
performs  the  function  thus  designated. 

In  the  preceding  examjole,  it  is  a  cj[uestion  of  inovements  carried  out  in  tlie 
same  situation  and  by  the  same  muscles,  movements  which,  according  to  tlieir 
degree  of  complication,  require  a  systematization  in  itself  more  or  less  compli- 
cated and  extended  in  the  nervous  system.  If  we  now  consider  movements  carried 
out  in  different  and  apparently  indei3endent  localities,  the  systems  which  co- 
ordinate them  perform  their  functions,  to  a  certain  degree,  independently  the 
one  of  the  other  ;  but  this  independence  is  scarcely  ever  absolute.  Between 
juxtajjosed  or  parallel  systems  bonds  of  union  exist,  sometimes  close,  sometimes 
lax,  by  wliich  they  interpenetrate,  and  thus  secure,  amidst  incessant  variety 
the  unity  of  the  nervous  system.  Further,  it  must  be  understood  tliat  their 
limitation,  sucli  as  we  conceive  it  in  order  to  describe  them,  is  in  a  great  degree 
arbitrary  ;  it  corresponds  in  each  case  to  an  external  phenomenon  of  movement 
which  we  have  ourselves  conventionally  limited  for  the  pvu'pose  of  analysis. 
Instead  of  definite  limits  separating  distinct  nervous  territories,  it  is  rather  a 
progressive  laxity  of  the  bonds  of  union  between  neighbouring  elements  and 
systems  the  existence  of  which  must  be  admitted  in  order  to  faithfully  represent 
the  condition.  It  must  be  added  that  these  boundaries,  thus  vaguely  pointed 
out,  cliange  at  every  moment,  according  to  the  variations  of  function. 


4.  The  centres. — This  organization  of  nervous  elements  into  systems 
and  sub-systems  of  varying  complexity  which  excite  and  co-ordinate 
functions  should,  in  our  opinion,  be  substituted  for  the  conception  of 
centres,  on  which  has  been  conferred,  by  a  priori  reasoning,  this  power 
of  excitation  and  co-ordination.  If,  however,  as  is  the  custom,  th& 
term  '•  centre  "  is  applied  to  those  regions  of  the  grey  matter  in  which 
the  anatomical  and  functional  bonds  of  union  between  elements  and 
systems  are  established,  this  expression  may  be  maintained  ;  but  it 
is  necessary  to  confine  the  idea  which  it  implies  to  that  of  the  con- 
nexions which,  in  the  grey  matter,  exist  between  the  components  of  the 
systematic  aggregations.  This  definition  does  not  correspond  to  the 
etymology  of  the  word,  but  it  represents  the  exact  truth.  In  fact,  we 
see  that  those  areas  of  the  grey  matter  which  are  known  as  centres 
are  the  more  extensive  and  more  numerous  in  proportion  as  the  func- 
tion is  higher,  and  as  its  movements  are  more  complex  and,  it  may  be 
said,  more  spontaneous.  These  so-called  centres  are  one  of  the  im- 
portant conditions  of  the  systematization  :  they  explain  it  to  us. 

To  take  an  example,  the  vaso-motor  nerves  (that  is  to  say,  nerves 
of  the  circulation)  form  a  system  of  this  kind  which  is  simpler  than 
the  preceding  ones,  whose  associating  neurons  extend  outside  the 
vertebral  canal,  towards  the  ganglia  of  the  great  sympathetic.  This 
last  seems  clearly  to  be  a  systematized  assemblage  of  neurons  which 
preside,  not  merely  over  the  circulation,  but  also  over  other  analogous 
functions. 


PRIMARY  SYSTEMATIZATIONS  247 

1.    The  nervous  system  and  heat.    The  thermic  nerves 

C  ellular  activity  declares  itself  very  generally  by  more  or  less  apparent 
movement  ;  it  is  rendered  evident  still  more  generally  by  a  develop- 
ment of  heat.  The  muscle  which  contracts,  the  gland  which  secretes, 
both  become  warmer,  the  one  more  than  the  other,  but  both  to  a 
sensible  degree.  This  development  of  heat  is,  like  movement  itself,  an 
evidence  of  the  activity  of  the  organs  and,  indirectly,  of  the  nerves 
which  preside  over  them.  The  motor  (or  secretory)  nerves  are,  then, 
from  the  very  fact  that  they  are  motor,  thermic  or  calorific  nerves. 
The  inhibitory  nerves  are  those  which  hinder,  not  only  the  occurrence 
of  movement,  but  also  the  disengagement  of  heat.  They  should  not 
be  called  frigorific,  as  they  have  sometimes  been  described,  because 
in  reality  they  do  not  cause  the  absorption  of  the  external  heat  by  the 
organs,  but  only  hinder  the  latter  from  producing  it. 

1.  Cellular  exciting  function  of  disengagement  of  heat. — However 
this  may  be,  the  disengagement  of  heat  being  the  most  general  pheno- 
menon of  the  activity  of  the  cell,  there  is  no  nerve  which  either  directly 
or  indirectly  does  not  influence  thermogenesis.  On  the  other  hand, 
this  development  of  heat  being,  like  movement  itself,  merely  one  of 
the  aspects  of  cell  function,  it  follows  that  all  the  nerves  which  directly 
or  indirectly  give  rise  to  movement,  are  hence  thermic  nerves  ;  and 
reciprocallj^  there  are  no  thermic  nerves  but  those  which  influence 
movement.  In  other  words,  the  thermic  nerves  are  not  distinct  from 
the  motor  nerves,  but  are  merely  these  latter  nerves  regarded  from  the 
point  of  view  of  their  connexion  with  heat,  instead  of  with  movement, 
the  two  things  being,  in  fact,  merely  two  different  aspects  of  the  same 
function. 

2.  Systematic  regulative  function  of  temperature. — From  the  cellu- 
lar point  of  view,  the  function  of  the  thermic  nerves  is  confounded 
with  that  of  motor  nerves.  But  it  is  none  the  less  true  that  (in  the 
superior  vertebrata)  there  is  a  function  for  the  regulation  of  heat,  and 
this  function  makes  .use  of  a  special  system  of  co-ordinated  nerves  in 
order  to  obtain  a  fixed  temperature  ;  a  system  in  which  the  nerves 
strictly  called  motor  only  partially  enter  with  the  purpose  of  increasing 
or  diminishing,  according  to  circumstances,  the  heat  produced,  together 
with  other  nerves  which  increase  or  diminish,  also  according  to  cir- 
cumstances, its  loss  by  the  skin  and  lung,  in  such  a  way  that  this  fixed 
thermic  level  may  be  maintained  by  compensations  in  spite  of  the 
variations  of  external  temperature. 

This  is  one  of  the  most  cogent  examples  of  the  dependence  of  the  2^^*^^ 
on  the  whole,  and  of  the  ichole  on  the  part,  which  is  one  of  the  character- 
istics of  the  animal  organization. 


248  SYSTEMATIC   FUNCTIONS 

The  systems  whicli,  by  the  association  of  elements  in  a  determinate  order, 
execute  those  functions  on  which  hfe  with  all  its  various  manifestations  depends, 
should  not  be  considered  as  juxtaposed  and  entirely  independent  aggregations. 
Indeed,  they  are  included  the  one  in  the  other,  as  the  part  is  in  the  whole.  It 
is  thus  that  the  system  which  subserves  the  emission  of  a  cry  is  included  in  that 
which  presides  over  phonation,  reflex  articulation,  thought  out  language  and 
that  which  is  the  result  of  reflection.  The  first  is  practically  the  foundation  and 
point  of  departure  of  the  others,  which  are  formed  by  successive  additions,  whose 
highest  portion  is  located  in  a  definite  region  of  the  cerebral  cortex. 

2.    The  nervous  system  and  nutrition.    Trophic  nerves 

Among  the  phenomena  whose  relation  to  the  nervous  system  is 
determined  by  observation  and  experiment,  there  are  some  simple, 
as  heat  and  movement  ;  but  there  are  also  others  whicli  are  compli- 
cated and  much  more  vaguely  defined,  such  as  those  which  are  included 
under  the  general  name  of  nutrition.  In  acting  on  the  nervous  system, 
heat  is  given  off,  and  we  have  seen  that  this  action  does  not  imply  the 
existence  of  special  nerves  conveying  a  specific  infiuence  to  the  cells, 
but  that  it  is  confounded  with  the  general  stimulation  of  the  cells  by 
the  motor  nerves.  By  acting  on  the  nervous  system,  the  nutrition  of 
the  tissues  under  the  influence  of  nerves  may  also  be  disturbed,  and  it 
is  necessary  to  point  out  that  this  perturbation  is  once  more  merely 
a  consequence,  more  remote,  indeed,  of  the  want  or  excess  of  functional 
activity  (according  to  circumstances)  which  follows  the  nerve  altera- 
tion, and  is  not  a  specific  influence,  conveyed  to  the  cells  by  anatomi- 
cally distinct  nerves,  such  as  trophic  nerves  would  be. 

In  principle,  this  tendency  to  admit  as  many  varieties  of  nervous 
action  as  there  are  of  relations  between  the  nervous  system  and  the 
organs  which  depend  on  it,  is  unscientific,  and  reasoning  easily  proves 
that  it  is  ill-founded. 

1.  Immediate  and  consecutive  influence  of  the  nervous  system  on 
the  Tissues. — Alteration  of  the  muscles. — Section  of  the  nerves  which 
supply  the  muscles  causes  the  immediate  paralysis  of  the  latter,  that  is 
to  say,  the  cessation  of  the  disengagement  of  energy  (heat  and  mechani- 
cal work)  by  which  their  activity  is  manifested.  And  a  further  remote 
consequence  is  a  structural  modification  of  the  muscle  fibre,  which 
loses  its  histological  characters  and  atrophies  ;  this  atrophic  degenera- 
tion is  a  consequence  of  the  permanent  loss  of  activity  of  the  7nuscular 
element.  Three  conditions  are  essential  to  the  cellular  life  :  a  fresh 
supply  of  nutritive  substance,  supply  of  energy  (which  is  indeed  allied 
to  this  substance),  supply  of  the  stimulus  which  makes  use  of  this 
energy  and  of  this  matter  ;  if  one  only  of  these  conditions  be  wanting, 
the  cell  will  be  in  danger  ;  it  is  a  general  law  of  which  this  is  only  a 
particular  instance. 


PRIMARY  SYSTEIVIATIZATIONS  249 

2.  Alterations  of  the  skin  and  of  the  cornea. — Ssction  of  nerve  trunks 
which  are  in  connexion  with  the  skin  or  the  cornea  equally  brings  about, 
after  a  certain  time,  alterations  of  these  structures  (opacity,  ulceration, 
etc.).  These  disturbances  of  nutrition  have  been  and  still  are  one  of 
the  strongest  arguments  appealed  to  by  those  who  maintain  the  exist- 
ence of  an  independent  species  of  nervous  activity,  specifically  trophic  ; 
and  the  force  of  the  argument  lies  in  this,  that  nerves  analogous  to 
the  exciting  nerves  of  the  muscles  are  not  known  to  be  distributed  to 
the  skin  or  to  the  cornea  in  order  to  provoke  and  govern  the  functions 
of  these  organs.  But  this  arises  doubtless  from  the  fact  that  this 
function,  itself  of  a  chemical  or  molecular  nature,  eludes  our  means  of 
authentication,  and  does  not  manifest  itself  by  anything  immediately 
obvious  at  the  moment  of  the  section  or  the  stimulation  of  the  cutane- 
ous or  corneal  nerves.  The  structure  is  not  less  gravely  altered  by 
lesion  of  nerves  which  preside  over  it,  and  this  alteration  is  only  made 
manifest  by  its  remote  effects,  that  is  to  say,  by  the  structural  degener- 
ation which  is  the  necessary  consequence  of  the  perversion  of  function. 

In  short,  the  so-called  trophic  nerves  are  not  only,  like  the  so-called 
thermic  nerves,  those  which  promote  the  special  function  of  the  organ  to 
which  they  are  distributed  ;  they  are,  histologically  speaking,  the  same 
fibres.  It  must  be  assumed  that  these  exciting  nerves  are  distributed 
to  all  the  fixed  elements  of  the  organism,  at  any  rate  to  the  greater 
number  of  them.  Where  the  function  is  obvious,  they  appear  to  be 
both  excitors  of  function  and  regulators  of  nutrition.  Where  the 
function  is  unknown  or  dissimulated,  they  appear  only  as  trophic 
nerves.  It  is  this  which  has  given  rise  to  the  belief  that  these  are 
distinct  and  independent  nerves  specially  devoted  to  nutrition. 

Unity  of  function  and  unity  of  cell  excitation. — As  regards  a  given  single 
nerve  element,  there  only  exists  a  single  order  of  neuron  ;  that,  namely,  which 
arouses  the  special  function  of  the  element.  In  this  function,  relatively  simple 
(cellular  function),  but  liaving  multiple  and  divers  aspects,  e^^erything  is  closely 
connected  ;  the  excitation  or  the  non-excitation  to  which  we  subject  it  by  our 
exjoeriments  on  the  nervovis  system  causes  the  develoiDment  of  a  consecutive 
series  of  phenomena  suggesting  those  which  are  the  result  of  its  normal  or  even 
pathological  activity.  The  bond  of  iinion  which  gathers  together  these  pheno- 
mena under  a  common  dependence,  and  gives  to  each  cell  its  functional  iinity, 
has  nothing  to  do  with  the  nervous  systein  ;  it  is  internal  to  the  cell  itself,  very 
different  from  that  which  organizes  the  functional  sj^stems  and  which,  effected 
between  the  elements  of  the  system,  is  located  in  its  turn  internally  to  the  latter. 
To  return  to  the  nature  of  the  nerve  action  by  which  this  bond  of  union  between 
the  elements  in  the  constitution  of  the  systems  is  realized,  we  repeat  that  it  is 
univocal  ;  it  can  be  only  excitor  or  inhibitory  ;  it  either  causes  the  evolution 
of  functional  manifestations  in  their  regular  succession,  or  it  hinders  their 
production  whatever  they  may  be  ;  it  regulates  neither  their  nature  nor  their 
particular  direction.     It  is  a  provoking  cause,  it  is  not  an  efficient  cause. 


250  SYSTEMATIC  FUNCTIONS 

3.    The  nervous  system  and  animal  chemistry 

Tlie  trophic  disturbances  whicli  result  from  tlie  functional  alterations  of  the 
nervous  system  have  diverse  ways  of  displaying  themselves,  such  are  :  atrophies, 
hypertrophies,  deviations  of  the  external  form  of  apparatus  and  organs,  all 
directly  appreciable  to  observation.  These  macroscopic  changes  are  caused  by 
microscopic  alterations  of  the  comjsonent  cells  of  these  parts.  If  we  carry  the 
analysis  farther,  we  see  that  these  so-called  elementary  alterations  dejoend,  in 
their  turn,  on  structures  of  a  still  more  elementary  character,  internal  to  the 
cell,  in  a  word  molecular,  and  which  are  thus  the  foundation  of  the  organization 
of  the  living  being.  These  molecular  structures  are  nothing  else  than  those  which 
chemistry  studies  by  its  ajDpropriate  methods  when  it  desires  to  examine  the 
constitution  of  different  substances,  from  simple  bodies  uj)  to  albumen,  for 
example. 

The  degrees  of  organization. — The  organization  of  the  living  being  tlius  forms 
a  continuous  and  regularly  graduated  series,  whose  point  of  departure  is  situated 
in  tlie  chemical  elements  ;  to  interfere  with  this  series  is  to  compromise  the  entire 
edifice  ;  to  maintain  it  in  its  integrity  is  one  of  the  concUtions  essential  to  its 
I^ersistence  and  its  solidity.  It  is  for  this  reason  necessary-  to  examine  the 
connexions  of  the  nervous  system  with  animal  chemistry. 

Convergence  of  the  phenomena. — Between  a  tissue  thus  highly  differentiated 
and  structiu'es  of  molecular  order  (that  is  to  say,  the  most  inferior),  the  con- 
nexions are  not  evident  at  the  first  glance.  They  are  better  understood  if  it  is 
remembered  that  the  molecular  phenomena,  internal  to  the  cell,  are  mutually 
subordinated,  cyclic,  converging  towards  a  definite  end,  and  that  their  final 
result  may  thus  be  as  simple  as  their  mechanism  is  complicated.  Two  cellular 
elements,  two  organized  systems,  may  thus  possibly  react  on  one  another  in  a 
very  simple  manner.  The  stimulation  of  the  tissues  by  the  nerves  is  an  act  of 
this  kind.  Very  simple  in  itself,  it  is,  as  regards  the  stimulating  tissue,  the  initial 
phenomenon  of  another  equally  complicated  series  of  cyclic  and  convergent 
acts. 

Nutritive  equilibrium. — Trophic  distiorbances  are  revealed  to  us  by  a  change 
in  tlie  form  and  structure  of  organs.  It  is  necessary  to  remember  in  this  con- 
nexion that  the  structure,  molecular  (or  otherwise)  of  these  parts  is  not  a  static 
condition,  but  that  tlie  persistence  of  their  forms  marks  an  incessant  renewal  of 
the  organized  substance. 

Tliis  jjersistence  is  the  index  of  the  regularity  of  this  renewal.  From  the  fact 
that  the  structure  of  the  organs  depends  on  an  equilibrium  which  is  thus  perjjetu- 
ally  mobile,  a  directing  influence  is  necessary  which  is  cajoable  of  effecting 
between  the  forces  which  co-operate  in  it  the  compensations  required  to  main- 
tain it  within  its  correct  limits  ;  and  the  nervous  system,  so  far  as  regards  the 
functions  with  which  we  are  acquainted,  apj^ears  to  us,  once  again,  to  be  the 
most  appropriate  to  assume  this  directive  and  regulative  influence. 

The  actions  of  the  living  being  take  their  first  origin  in  the  chemical  reactions 
of  its  substance.  The  nervous  sysetm,  when  it  intervenes,  only  influences  these 
actions  through  the  intermediation  of  these  chemical  reactions.  What  is  the 
nature  of  the  influence  which  it  has  over  them  ?  But  flrst  of  all,  what  are  the 
reactions  themselves  ?     How  are  they  arranged  ? 

Reactions  of  the  organism. — Some  of  these  reactions  are  reversible  ;  the  others, 
irreversihle. 

(a)  Reversible  reactions. — A  phenomenon  is  called  reversible  when  it  consists 
in  a  change,  or  in  a  series  of  changes,  which  may  take  place  in  either  direction  from, 
the  initial  to  the  final  condition,  and  from  the  final  to  the  initial  condition,  by 
passing  precisely  the  same  intermediate  stages.  Example  :  oxygen  and  haemo- 
globin  being   submitted   (under    uniform    conditions    as    regards  temperature) 


PRIMARY  SYSTEMATIZATIONS  251 

to  increasing  pressure,  a  compound  wil]  result,  oxyhaemoglobin,  whose  quantity- 
is  in  a  direct  relationship  with  this  pressure.  If  the  jaressure  continuously  de- 
creases, the  quantity  of  oxy haemoglobin  will  decrease,  following  the  same  curve, 
but  in  an  opposite  direction.  There  is  thus  in  the  one  case  association  and  in 
the  other  chssociation  of  the  two  comjDonents,  and  hence  it  is  said  that  oxyhiemo- 
globin  is  a  dissociable  combination. 

(b)  Irreversible  reactions. — A  phenomenon  is  irreversible  when  it  consists  in 
a  change  or  a  series  of  changes  ivhich  can  only  take  place  in  a  determinate  direction, 
in  such  a  tcay  tJiat,  in  order  to  return  to  the  final  from  the  initial  condition,  it  is 
7iecessary  that  a  different  cycle  be  followed  from,  that  taken  in  proceeding  from  the 
initial  to  the  final  condition.  Example  :  from  the  glycogen  which  is  burnt  in 
contact  Avith  oxygen,  carbonic  acid  and  water  are  formed  ;  but  we  do  not  know 
of  any  means  by  which  this  process  can  be  inverted  (nor  even  any  means  in  the 
domain  of  ordinary  chemistry)  of  reproducing  glycogen  and  oxygen  with  this 
carbonic  acid  and  this  water.  The  formation  of  glycogen,  on  the  one  hand,  and 
its  destruction  on  the  other,  are  irre\'ersible  reactions. 

Chemical  equilibrium. — From  the  point  of  view  of  energj-,  reversible  and  irre- 
versible reactions  differ  profoundly. 

(1)  In  reversible  reactions. — In  the  first  the  chemical  equilibrium  is  constant 
and  stable  ;  according,  indeed,  to  the  state  of  the  temperature  and  of  pressure, 
combination  occurs  or  is  resolved  in  the  proportions  desired  in  order  that  this, 
ec^uilibrium  may  also  be  satisfied.  In  such  combinations  the  bodies  do  not 
accfuire  any  reserve  of  energy  or  any  potentiality. 

("2)  In  irreversible  reactions. — In  the  second  it  is  not  so  ;  the  complete  cycle 
of  the  phenomenon,  starting  from  a  given  initial  condition  in  order  to  return  to 
this  initial  condition,  manifests  indeed  in  its  turn  two  orders  of  reactions  which 
are  inverse,  but  not  symmetrical,  as  is  the  case  with  the  first. 

(a)  Ascending  phase. — In  the  first  phase,  the  reacting  bodies  absorb  and 
accumulate  in  themselves  a  certain  quantity  of  energy  which  is  connected  with 
the  particular  position  wliich  their  molecules  assume  within  them  ;  the  reaction 
is  then  called  endothermic.  Example  :  the  radiant  solar  enei'gj-  is  absorbed  by 
plants  for  the  synthesis  of  starch  ;  the  molecules  of  the  body  thus  prodviced  are 
in  iinstahle  equilibrium,  the  energy  accumulated  in  it  to  give  the  molecules  their 
particular  position,  is  always  ready  to  be  expended  in  order  to  make  them  leave 
this  position  and  destroy  this  body  by  giving  rise  to  new  combinations.  The 
energj'  thus  stored  up  is  called  its  reserve  or  potential  energy  ;  the  body  is  called 
explosive. 

(b)  Descending  phase. — In  the  second  phase,  this  unstable  equilibrium  is 
destroyed  ;  the  molecules  lose  their  relative  situation,  new  combinations  make 
their  apj^earance,  the  enei'gy  held  in  reserve  becomes  free  and  is  manifested  in 
the  form  of  heat  or  of  mechanical  work  ;  the  reaction  is  then  called  exothermic. 
Example  :  starch  (or  glycogen)  in  contact  with  oxygen  is  transformed  into  car- 
bonic acid  and  water,  with  disengagement  of  all  the  radiant  energj'  which  has 
been  absorbed  by  the  plant  in  order  to  produce  this  combination. 

Rupture  of  equilibrium. — The  irreversible  cycle  differs,  as  is  obvious,  from  the 
reversible  cycle,  inasmuch  as  it  has  a  definite  direction  of  which  the  different 
stages  can  be  recognized.  An  ascending  j^hase  can  be  determined,  during  which 
energy  is  stored  up,  and  a  descending  phase,  or  that  of  expenditure  of  energj^. 
Between  the  two  occurs  the  phenomenon  of  rupture  of  molecialar  eciuilibrium, 
and  this  opens  the  second  phase. 

Energy  of  disengagement. — This  I'upture  of  equ^ilibrium  requires  the  inter- 
vention of  an  energy  which,  from  the  time  of  Helmholtz,  has  been  known  as  the 
energy  of  disengagement. 

Direct  nervous  action. — The  following  principle  may  be  regarded    as   indis- 


252  SYSTEMATIC  FUNCTIONS 

)3utable  :  the  nervous  system  can  only  have  a  direct  action  on  tlie  exothermic  re- 
actions of  the  organism  ;  that  is  to  say,  on  the  irreversible  reactions  which  give 
off  energy.  Itself  representing  an  infinitesimal  amount  of  energy  (energy  given 
off),  it  can  only  have  a  directly  efficient  action  in  overcoming  an  unstable  equili- 
brium. Its  duty  is  to  cause  an  expenditure  of  energy,  not  to  supply  it  to  the 
tissues.  Energy  arises  by  another  route  ;  it  is  supplied  by  the  aliments  which 
have  been  stored  uj),  and  which  the  circulation  distributes  to  these  tissues  in  the 
form  of  somatic  or  cellular  reserves. 

The  comparison  of  the  ingesta  with  the  excreta  well  shows  this  alimentary  origin 
of  energy.  The  heat  of  combustion  of  the  first  is  considerable,  that  of  the  second 
is  almost  nil  ;  the  difference  between  the  two  precisely  measures  the  quantity 
of  energy  which  the  animal  organism  gives  off  in  the  course  of  the  transformations 
which  the  first  undergo  in  order  to  become  the  second.  It  is  the  duty  of  the  nervous 
system  to  control  and  to  direct  this  expenditiue  of  energy,  by  exciting  the  trans- 
formative reactions  by  means  of  which  the  excreta  are  derived  from  the  aliments. 

Syntheses  in  animals. — If,  however,  these  transformations,  in  their  totality, 
follow  a  general  curve  which  may  be  called  descending,  it  is  not  less  certain  that, 
from  their  initial  state  (aliments),  to  their  final  condition  (excreta),  they  present 
certain  oscillations  in  the  course  of  which  energy  is  now  liberated,  now  absorbed, 
before  being  finally  almost  totally  expended.  Alongside  of  these  analytical 
reactions  which  characterize  animal  chemistry  in  the  general  cycle  of  the  living 
kingdom  (vegetable  and  animal),  there  are  synthetic  reactions  which  take 
place  in  the  animal  resembling,  if  not  identical  with,  those  which  occur  in  the 
vegetable. 

Indirect  nervous  action. — In  the  animal  which  possesses  a  nervous  system,  as 
in  the  vegetable  wliich  possesses  none,  these  synthetic  reactions  elude  the  direct 
action  of  this  special  system. 

(a)  On  the  irreversible  endothermic  reactions. — Xevertheless  thej-  may,  in  an 
indirect  manner,  fall  once  again  under  its  influence,  in  the  sense  that  the  portion 
of  the  energy  rendered  free  by  the  exothermic  reactions  may  be  utilized  in  situ 
for  the  performance  of  endothermic  reactions  which  require  an  unappropriated 
energy  in  order  to  be  carried  out.  The  heat  given  off  by  the  cells  during  their 
functional  activity  would  here  perform  the  office  of  the  solar  radiations  by  which 
the  syntheses  of  vegetables  are  effected  ;  and  thus  would  be  explained  the  inti- 
mate bond  of  union  which  exists  in  the  cells  between  the  expenditvire  of  energy 
of  M'hich  they  are  the  seat  and  there-accumulation  of  their  available  reserves  in 
proportion  to  their  exhaustion. 

(b)  On  the  reversible  reactions. — As  regards  the  reversible  reactions,  inasmuch 
as  their  characteristic  is  that  of  presenting  a  constant  molecular  equilibrivmi,  the 
energy  of  disengagement  which  circulates  in  the  nervous  system  has,  in  their 
case,  no  hold  on  them.  Where  equilibritim  is  stable,  there  can  be  no  rupture  of 
equilibrium.  Bvit  these  reactions  may  eqvially,  like  the  preceding,  fall  once 
again  vmder  the  influence  of  the  nervous  system  in  a  roundabout  way  ;  for  this 
to  be  so  it  suffices  that  the  conditions  of  temperature  and  of  pressure  on  which 
they  dei^end,  be  themselves  changed  through  nervous  action,  that  is  to  say,  as 
the  direct  consequences  of  this  action. 

Example. — This  is  what  happens  in  the  muscle,  when,  as  the  result  of  the 
stimulation  of  its  nerve,  the  oxygen  contained  in  its  plasn:ia  acts  on  the  glycogen 
in  order  to  burn  it  up  ;  the  condition  of  the  temperature  is  not  markedly  changed, 
but  the  tension  of  the  gases  is  considerably  so.  The  glycogen,  in  order  to  he 
transformed  into  carbonic  acid,  absorbing  the  oxygen  of  the  muscular  plasma, 
consequently  lowers  the  tension  of  this  gas  in  the  liquid  intracellular  medium. 
Hence  the  muscular  haemoglobin,  then  the  haemoglobin  of  the  blood,  are  dis- 
sociated.     Carried  away  by  the  venous  blood,  this   htemoglobin  finds  in  tlie  lung 


PRI^L^RY  SYSTEMATIZATIONS  253 

a  pressure  of  oxj^gen  sufficient  to  reproduce  the  oxj'lisemoglobin  combination 
wliicli  has  been  destroyed  in  the  muscle,  and  this,  in  its  tvirn,  carried  away  bj^ 
tlie  arterial  current  to  the  muscle,  will  again  be  destroyed  in  it,  and  so  on. 

Initial  phenomena. — The  point  of  departure  of  these  changes  is  not  located 
in  the  lung,  as  seems  often  to  be  thought,  biit  rather  in  the  tissues,  and  the  initial 
phenomenon  is  a  nervotis  excitation  whose  consequences  are  gradually  felt  through- 
out the  economy,  indirectly  it  is  true,  but  inevitably. 

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Inhibition  in  the  Invertebrata. — Phisalix,  Centres  inhibitoires  des  taches  pigmen- 
taires  des  eeplialopodes,  Arch.  Phys.,  1894,  p.  92. — Piotrowski,  Muscle-nerve  Phvsiol. 
of  the  Craj-fisch,  Journ.  of  Phys.,  1893,  p.  163. 

Shock. — Bastian,  Med.  chir.  Trans.,  London,  1891. — Bethe,  Arch.  f.  d.  ges.  Phys. 
Bd.  LXVIII.— Bruns,  Neurol.  Centralbl.,  1893.— Contejean,  Arch.  Phys.,  1894,  p.  643, 
— Fr.-Franck,  Biol.,  1877  ;  Trav.  lab.  Marey,  1877. — Loeb,  Arch.  f.  d.  ges.  Phys.,  1894. 
Bd.  LVI. — Marsh.all-Hall,  Sjoiopsis  of  the  Diastaltic  Xervous  Sj-stem,  London,  1850. 
— W.-W.  XoRiiAN,  Arch.  f.  d.  ges.  Phys.,  1897,  Bd.  LXVII.— Pikchaud,  These  de  Paris. 
—Roger,  Arch.  Phys.,  1893,  p.  57,  601,  177;  et  1894,  p.  783.— Sherrington,  Phil. 
Trans.,  London,   1897. 

Stoppage  of  the  Exchanges. — Bro'svn-Seqtjard,  C.  P.  Acad,  sc,  1882,  t.  XCIV,  p.  491  : 
Arch,  de  phys.,  1891,  p.  818. 

Trophic  Nerves. — Cl.  Bernard,  Biol.,  1873. — Bichat,  Rech.  sur  la  vie  et  la  mort. 
Paris,  1829,  5*^  edit.,  p.  506. — Bidder,  Centralbl.  f.  d.  med.  Wiss,  1874. — B.  Brodie, 
cite  par  Brown-Sequ.ard,  Journ.  de  la  phys.  homme  et  anim.,  1859,  p.  114. — Charcot, 
LeQons  svu'  les  maladies  du  syst.  ner\'.,  1872-1873,  p.  133. — Couyba,  These  de  Paris, 
1871. — DuPLAY  et  MoRAT.  Mai  perforant  plantaire.  Arch.  gen.  de  med.,  1873. — H.  Fremy, 
Trophone\-rose,  These  de  Paris,  1872. — Knoll,  Sitz.  d.  k.  Acad.  Wiss.,  \^"ien,  1893. — 
Le  Lande,  Aplasie  lamineuse.  These  de  Paris,  1870. — Legro.s,  Des  vaso-moteurs.  These 
ag.  Paris,  1873. — Longet,  Traite  de  physiol.,  3''  edit,  t.  Ill,  p.  539.- — Magendie,  Journ. 
de  phys.  cxp.,  1824. — Marinesco,  Neurol.  Centralbl.,  1898. — G.  Meissner,  Gaz.  hebd., 
1867. — Obolensky  Gaz.  hebd.,  1868,  p.  590. — Ollier,  Journ.  de  la  phys.  homme  et  anim., 
1863,  t.  VI,  p.  107. — Samuel,  Die  trophischen  Xerven,  Leipzig,  1860. — Schiff,  Biol., 
1854,  Gaz.  hebd.,  1857. — Sherrington,  Proceed.  Boy.  Soc,  1896. — Stirling,  Journ. 
Anat.  and  Phys.,  1876,  vol.  X,  p.  511. — Vulpian,  Lemons  sur  I'app.  vaso-moteiu',  t.  II. — 
Warington,  Journ.  of  Phys.,  1897. 


CHAPTER    III 

THE  CONSCIOUS  AND  THE  UNCONSCIOUS  :    THEIR 

SEPARATION 

We  have  seen  that  the  nervous  system  is,  m  a  sense,  divided  into  two 
portions,  which  we  call  sensory  and  motor,  the  characters  of  which  have 
be  en  pointed  out.  From  another  point  of  view  it  is  divided  into  two 
great  systematizations  which  are  founded  on  another  opposition,  that 
which  exists  between  the  conscious  and  the  unconscious  nature  of 
certain  acts  or  functions  which  it  performs.  This  opposition  is  no 
more  absolute  than  is  that  observed  between  sensation  and  motion  ; 
but  it  seems  to  us  to  be  so  on  account  of  the  highly  marked  distinction 
which  exists  between  the  different  states  of  consciousness. 

The  degrees  of  consciousness. — There  is  an  obscure  consciousness  of 
being  which  does  not  analyse  either  the  forms  or  the  movements  or 
the  causes  of  these  movements  ;  this  is  never  absent  from  our  organs 
so  long  as  they  are  attached  to  the  nervous  system  as  a  whole,  and  we 
may  conclude  that  it  exists  to  some  extent  in  the  separate  cellular 
elements  ;  it  is  a  form  of  unconsciousness,  which  is  practically  only  sub- 
consciousness. There  is  a  definite  consciousness  of  being  which  is  sharply 
defined  from  that  which  surrounds  it,  and  furnishes  it  with  the  forms, 
the  cj[ualities  and  the  movements  which  come  in  relation  with  it  from 
the  external  world  ;  this  is  the  perception  of  the  ego,  consciousness 
properly  so  called. 

1.  Separation  at  the  periphery, — It  is  remarkable  that  the  most 
definite  consciousness  arises  from  the  most  sharply  accentuated  opposi- 
tion between  that  which  is  internal  to  us  and  tha.t  which  is  external 
to  us  ;  namely,  of  the  excitations  from  the  surface  of  our  bodies  (organs 
of  sense)  reverberating  on  muscles  capable  of  reacting  against  the 
causes  of  thase  excitations  ;  while  our  own  organs,  in  exchanging 
between  themselves  excitations  and  reactions  by  the  intermediation 
of  the  nervous  system,  only  furnish  us  with  sensations  which  are  ob- 
scure, without  precision,  indefinite,  incapable  of  analysis.  The  sensory 
nerves  which  start  from  the  surface,  the  motor  nerves  which  return 
to  the  superficial  muscles,  these  are  concerned  with  the  cycle  of  con- 


CONSCIOUS  AND  UNCONSCIOUS  ;    THEIR  SEPARATION    257 

sciousness.  The  sensitivo-motor  elements  embedded  in  the  depths 
of  the  body,  these  are  related  to  unconsciousness.  Anatomically 
speaking,  the  separation  is  here  very  definite  ;  on  the  one  hand  a 
somatic  system,  on  the  other  a  splanchnic  system  whose  characters  will 
be  analysed  farther  on. 

2.  Separation  in  the  cerebral  cortex. — Everywhere  else  the  separa- 
tion is  much  more  difficult  to  make.  Distinct  sensation,  the  conscious 
phenomenon,  is  only  developed  as  regards  a  cycle  which  includes  the 
cerebral  cortex.  But  the  converse  is  not  true,  although  it  is  often 
affirmed  to  be  so.  Certain  cycles  which  are  completed  in  the  cortex 
do  not  end  in  a  conscious  sensation  in  the  ordinary  sense  of  the  word. 
This  is  due  to  the  greater  or  less  extension  which  the  excitation  effects 
in  the  cortex,  and  to  the  facility  of  penetration  which  is  here  offered 
to  it,  according  to  the  point  of  departure  and  the  intensity  of  excita- 
tion. Those  excitations  which  come  from  the  senses  have  easy  access 
to  it,  those  coming  from  the  internal  organs  a  difficult  one  ;  but  it  is 
a  question  of  degree. 

3.  Separation  between  the  deep  and  the  peripheral  systems. — On  the 
other  hand,  the  excitation  which  has  penetrated  into  the  nervous 
system,  especially  in  the  cortex,  is  provided  with  means  of  remaining 
there  when  the  communications  with  the  organs  of  the  senses  are 
broken.  The  cycle  of  excitation  is  then  spUt  up  in  the  direction  of 
its  elevation,  into  a  superior  cerebral  cycle  and  an  inferior  medullary 
cycle,  which  are  capable  of  independent  functional  action.  Hence 
results  a  new  division  between  the  conscious  and  the  unconscious  : 
consciousness  continues  attached  to  the  brain  in  the  form  of  souvenir 
or  remembrance  of  the  anterior  sensation  ;  unconsciousness  is  situated 
in  the  inferior  cycle  which,  in  spite  of  its  persistent  relations  mth  the 
organs  of  sense  and  the  muscles,  is  reduced  to  the  condition  of  a  reflex 
phenomenon. 

Variability  of  the  limits. — Consciousness  is  not  then  attached  to  a 
rigid  and  permanent  system  of  nerves,  and  stiU  less  to  a  special  kind 
of  cellular  element.  It  takes  its  rise  in  the  associations  which,  accord- 
ing to  the  requirements,  are  organized  in  the  nervous  system,  and  its 
degree  becomes  more  elevated  according  to  the  complexity  and  the 
special  value  of  these  associations.  More  uniform,  more  automatic 
are  those  of  the  visceral  functions  ;  while  the  somatic  functions  are 
more  contingent,  more  varied,  and  more  complex,  and  hence  it  is  that 
their  value  is  so  unequal  from  the  point  of  view  of  consciousness. 

In  the  analytical  study  which  follows  and  passes  in  review  the 
principal  localities  in  wliich  nervous  associations  are  organized,  we 
shaU  always  bear  in  mind  this  double  separation  between  sensibihty 

P.  s 


258  SYSTEMATIC  FUNCTIONS 

and  motricity,  between  the  conscious  and  the  unconscious.  It  is  at 
the  foundation  of  nervous  organization.  It  will  guide  us  constantly 
in  the  study  which  we  shall  proceed  to  make  of  the  latter  as  a  whole, 
before  describing  the  different  modalities  or  special  functions  which 
introduce  into  it,  in  their  turn,  numerous  subdivisions. 

The  problem  of  the  conscious,  its  difficulties  ;  current  hypothesis. — Botli 
naturally  and  by  definition,  consciousness  is  a  phenomenon  which  we  only 
directly  perceive  in  ourselves  The  first  classification  which  occurs  to  us  is  a 
distinction  between  our  being  and  that  wliich  sui'rounds  it.  The  ego  is  opposed 
to  the  non-ego.  The  ego,  which  is  conscious  of  its  being,  and  which  sees  beings 
outside  its  consciousness,  willingly  attributes  to  thein  unconsciousness,  by  oppo- 
sition to  that  which  it  feels  to  be  itself. 

The  conscious  and  unconscious  apart  from  ourselves. — It  is  true  that  this 
delusion  is  somewhat  rapidly  rectified  when  it  is  a  question  of  beings  situated 
outside  ourselves  which  narrowly  resemble  us  in  their  external  characters,  as 
human  beings  ;  or  which  have  considerable  analogy  with  us,  as  animals.  By 
indirect  procedures,  we  thus  recognize  the  existence  of  consciousness  other  than 
oru"  own.  On  the  other  hand,  the  delusion  is  more  endm-ing  in  proportion  as 
we  are  removed  from  these  special  cases.  At  the  first  glance,  it  does  not  seem 
that  consciousness  can  exist  except  under  the  form  and  in  the  degree  which  we 
recognize  in  ovirselves.  It  may  be  asked,  however,  if  consciousness  is  not  a 
frmdamental  attribute  of  the  being,  an  attribute  whose  complicated  and  very 
differentiated  form  in  oui'selves  hinders  us  from  recognizing  its  original  and 
general  nature.  This  manner  of  viewing  the  question  is  supported  by  the  con- 
temporary progress  of  biology.  In  proportion  as,  starting  from  ourselves,  we 
are  better  acquainted  with  the  filiation  which  attaches  us  to  other  beings,  so 
much  is  the  field  of  consciousness  in  nature  enlarged.  There  only  where  the 
chain  seems  to  us  broken,  at  the  line  of  separation  between  the  organic  and  in- 
organic, does  this  field  itself  seem  to  terminate.  But  continuity  may  one  day 
be  found  to  exist  where,  at  present,  we  see  only  discontinuity.  However  this 
may  be,  by  remaining  on  biological  territory,  as  it  is  at  present  defined,  it 
may  be  said  that,  outside  ourselves,  the  division  between  the  conscious  and  the 
unconscious  is  not  made  in  accordance  with  a  distinctly  traced  line,  but  follows 
a  zone  progressively  degenerating  without  determinate  limits. 

The  conscious  and  the  unconscious  in  ourselves. — In  our  own  propei  being 
there  is  a  division  between  tlie  conscious  and  the  unconscious.  The  ego  does  not 
always  occupy  the  whole  of  the  organism,  and  it  does  not  always  occupy  the 
same  field  in  the  latter.  All  that  remains  apart  from  the  conscious  field  we  call 
unconscious.     But  the  same  problem  presents  itself  liere  as  higher  up. 

Is  this  unconsciousness  which  is  present  in  us  an  unconsciousness  in  the  abso- 
lute sense  of  the  word,  or  rather  is  it  a  consciousness  which  is  limited  to  what  is 
outside  the  ego  ?  If  we  notice  that  the  nervous  mechanisms  which  record  these 
so-called  unconscious  functions  are  (although  of  less  elaborate  nature)  built  up 
on  the  same  plan  as  those  which  take  part  in  conscious  functions,  we  must  admit 
that  the  second  supposition  is  the  more  probable  one.  The  anitnal  organism 
may  be  regarded  as  an  association  of  conscious  units  of  unequal  value,  and  in  which 
one  of  these  units  has  assumed  the  directive  action  (Durand  de  Gros). 

Animal  colonies. — Phylogenetic  development  seems  to  support  this  concep- 
tion. As  is  well  known,  the  invertebrata  are  composed  of  segments  (zoonites), 
each  one  representing  in  miniature  the  organization  of  the  animal  to  which  they 
belong.  Isolated  the  one  from  the  other,  they  are  yet  susceptible  of  vital  mani- 
festations presenting  a  certain  independence  (Duges). 


CONSCIOUS  AND  UNCONSCIOUS  ;    THEIR  SEPARATION    259 

In  the  vertebrata,  tlie  zoonites  have  become  the  metameres  and  have,  funda- 
mentally, the  same  signification.  Metamerisation,  at  first  clearly  obvious  in 
the  embryo,  is  in  the  process  of  development  reduced  to  a  mere  trace,  and  thus 
gives  place  to  a  very  definite  centralization  in  superior  animals,  especially  in 
man.  The  vertebrata,  according  to  this  hypothesis,  would  not  be  the  less  an 
animal  colony  (E.  Perrier),  in  which  one  of  the  conscious  imits  (that  which  we 
call  the  ego)  has  taken  the  control  of  the  whole  and  has  reduced  the  other  units 
to  tlie  condition  of  conscious  servants  having  no  initiative,  servants  so  eclipsed 
that  it  ignores  the  initial  filiation  by  which  they  are  united  to  it. 

Difficulties  of  the  analysis  of  the  phenomena  of  consciousness. — There  would 
be  then  in  the  living  being  an  organization  of  consciovisness,  just  as  there  is  an 
organization  of  force  and  of  matter,  and  it  is  this  very  organization  whose  chief 
outlines  would  be  rendered  visible  by  the  form  and  the  strvicture  of  animals. 
These  are  simple  indications  reduced  to  a  vague  and  indefinite  condition.  When 
analysis  endeavom-s  to  penetrate  into  tliis  domain,  inextricable  difficulties  are 
encoimtered.  Consciousness  is  the  most  imperceptible  and  the  most  mobile 
phenomenon  which  it  is  possible  to  stvidy.  We  know  that  it  is  susceptible  of 
augmentation,  of  reduction,  of  disintegration,  of  synthesis.  Its  field  of  action 
varies  at  every  moment,  absorbs  neighboiu-ing  fields,  or  is  detached  from  them, 
undergoes  degradations,  and  passes,  according  to  circumstances,  into  the  sub- 
conscious, the  unconsciovis,  or  the  extra-consciovis.  Consciousness  is  like  the 
living  being  in  a  condition  of  perpetual  renewal,  of  perpetual  genesis. 

A.     DISPERSION  AND  REFLECTION  OF  IMPULSES  :  THE  SPINAL  CORD. 

The  nerve  roots  are  only  conductors  of  the  impulse.  In  the  spinal 
cord  these  conductors  are  associated  ;  through  its  grey  matter  it  be- 
comes an  apjmratus  for  the  transformation  of  the  impulse  and,  therefore, 
for  the  organization  of  the  nervous  functions. 

The  grey  matter  wherever  it  occurs  is,  if  we  may  call  it  so,  the  key- 
stone of  the  systems  by  which  these  functions  are  carried  out.  By  it 
the  connexions  between  the  neurons  are  effected,  the  neurons  being 
those  which  make  up  these  connexions  and  contain  the  breaks  which, 
at  other  times,  dissociate  them  in  order  to  substitute  them  reciprocally. 
Erom  this  point  of  view  the  functions  of  the  spinal  cord  have  for  long 
been  divided  into  two  groups  :  the  one  including  those  which  are  per- 
fected in  inferior  and  very  simple  systems,  organized  in  it,  and  which 
suffice  for  the  performance  of  very  simple  functions  {reflex  systems  and 
functions)  ;  the  other  including  those  in  which  these  inferior  systems, 
dissociating,  yield  up  their  elements  for  the  constitution  of  much  larger 
systems  {conscious  voluntary  systems  and  functions). 

They  are  distinguished  by  the  fact  that,  in  the  first  case,  the  spinal 
cord  acts  as  a  centre  of  reflection,  and  in  the  second  as  an  organ  of  trans- 
mission. The  two  varieties  do  not  differ  fundamentally,  for  both 
imply  the  reflection  and  transformation  of  the  impulse  in  the  grey 
matter.  The  difference  consists  rather  in  that,  in  the  first  case,  reflec- 
tion occurs  towards  the  exterior,  in  a  manner  which  is  both  direct  and 
total ;  while,  in  the  second,  it  is  effected  towards  the  depths  of  the  nervous 


260  SYSTEMATIC    FUNCTIONS 

system,  in  which  the  impulse  is  dispersed,  undergoing  multiple  and 
graduated  reflections  and  transformations  which  generally  absorb  it  in 
great  part. 

The  word  "  spinal  cord,"  in  the  sense  in  which  it  is  used  in  descriptive  anatomy, 
does  not  imply  an  organ  having  natural  limits,  but  has  merely  the  value  of  a 
topographical  expression.  In  order  to  isolate  this  so-called  organ,  the  scalpel 
of  the  anatomist  separates  the  conducting  fibres,  some  of  which  attach  it  to  the 
brain  (deep  neurons  or  those  of  the  second  order),  and  others  to  the  non-nervous 
organs  (peripheral  neurons  or  those  of  the  first  order).  These  neurons  are  con- 
nected amongst  themselves  in  the  spinal  cord  itself,  as  also  with  other  neurons 
which  are  special  to  it.  The  limits  of  the  elements  and  of  the  systems  formed 
by  the  associations  of  these  elements  are,  on  the  contrary,  situated  in  the  grey 
matter.  This  latter  is  therefore,  by  definition,  a  place  of  organization  for  nervous 
functions.  In  order  to  reach  it,  the  conductors  of  the  first  and  of  the  second 
order  (peripheral  and  encephalic)  both  run  a  certain  covirse  in  the  white  mediillary 
tracts,  where,  completely  isolated  from  the  point  of  view  of  conduction,  they  are 
more  or  less  intimately  mixed. 

An  analytical  study  of  the  functions  of  the  spinal  cord  must  therefore  be 
conunenced  by  the  recognition  of  these  different  elements,  by  seeking  to  isolate 
them  functionally  the  one  from  the  other,  by  ascertaining  their  properties  with 
the  help  of  localized  stimuli,  or  by  equally  localized  mutilations,  so  that  an  opinion 
may  be  formed  concerning  their  function,  either  by  its  artificial  excitation  or  by 
its  deficit.  The  leading  type  of  these  experiments  is  displayed  in  those  which 
have  been  performed  on  the  roots,  with  this  qualification,  however,  that  the 
object  under  investigation  has  become  much  more  complex,  and  that  the  experi- 
mental difficulties  are  therefore  so  much  the  greater. 

1.    Sensation  in  the  Spinal  Cord 

It  is  necessary  to  consider  apart  the  results  furnished  by  local  stimu- 
lations and  those  due  to  interruptions  or  equally  localized  sections  of 
the  medullary  tracts. 

A.  Stimulation  of  the  grey  matter. — It  has  for  long  been  maintained 
by  physiologists,  as  a  kind  of  dogma,  that  the  grey  matter  is  wholly 
inexcitable  by  irritants  applied  experimentally  (electricity,  pricking, 
chemical  action,  etc.).  Chauveau  had,  however,  proved  that  elec- 
trical excitation,  appHed  to  the  floor  of  the  fourth  ventricle,  threw 
into  activity  the  nuclei  of  the  motor  nerves  which  take  origin  therein. 
The  erroneous  idea  which  was  held  concerning  this  matter  was  not 
wholly  corrected  until  about  1870,  by  the  work  of  Fritsh  and  Hitzig 
on  the  stimulation  of  the  cerebral  cortex.  So  far  as  concerns  the  spinal 
cord,  Vitzou,  operating  on  the  inferior  ventricle  {rhomboidal  sinus)  of 
the  spinal  cord  of  birds,  has  shown  that  its  grey  matter  can  be  directly 
excited  by  mechanical  agents. 

1.  Excitation  of  the  centres. — It  is  now  common  knowledge  that,  by 
stimulating  certain  regions  of  the  grey  matter,  it  is  possible  to  elicit 
the  motor  properties  of  the  motor  nerves  which  take  their  origin  in 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    261 

them  :  this  is  what  is  called  the  excitation  of  the  centres  of  origin  of 
these  nerves.  Nevertheless,  it  seems  that  some  confusion  still  exists 
concerning  what  should  be  called  the  excitation  of  a  centre.  This 
confusion  arises  from  the  fact  that  an  inaccurate  and  indefinite 
idea  is  held  concerning  the  organization  and  the  functions  of  the 
centres. 

Erroneous  comparison. — Applied  to  a  nervous  conductor,  the  stimu- 
lus causes  the  manifestation  of  the  function  of  this  conductor  ;  applied 
to  a  centre,  it  is  maintained  that  it  should  arouse  the  much  more  com- 
plex functions  of  this  centre,  and  make  them  appear  in  their  normal 
order.  But  it  is  here  that  the  error  lies  ;  the  comparison  is  inaccurate. 
There  is  a  tendency  to  forget  that,  in  the  first  case,  the  stimulus  affects 
a  simple  (or  relatively  simple)  object,  Avhich  has  but  one  mode  of 
response,  by  allowing  it  to  pass  into  the  sensory  or  motor  organs,  with 
which  it  is  connected  ;  in  the  second  case,  the  stimulus  is  applied  to 
an  association,  a  complex  arrangement  of  elements,  all  of  which  it 
affects  at  the  same  time,  without  regard  to  the  special  order  according 
to  which  they  should  transmit  this  impulse  in  order  to  ensure  its  regular 
and  harmonious  effect.  It  is  as  if,  in  a  piece  of  clockwork,  the  impulse 
were  communicated  to  all  the  wheels  at  the  same  time,  without  any 
regard  being  paid  to  the  direction  or  to  the  rate  of  their  rotation  ;  the 
mean  effect  of  this  would  be  a  movement,  but  one  not  necessarily 
suggesting  that  which  arises  regularly  when  the  apparatus  is  controlled 
by  its  balance  wheel. 

Simultaneous  excitation  of  elements  arranged  in  succession. — Of 
whatever  nature  may  be  the  stimulus  made  use  of,  electricity,  mechan- 
ical irritation  (and  electricity  is  almost  the  only  efficacious  excitant), 
it  wall  reach  simultaneously  in  the  grey  matter  (in  that  which  we  call 
the  centres)  all  the  elements  of  which  it  is  composed,  whether  these 
elements  be  sensory,  motor,  inhibitory,  co-ordinating,  associating,  etc., 
it  will  place  them  in  irregular  conflict  the  one  with  the  other,  and  will 
give  the  predominance  to  some  of  them,  preferably  to  those  which  take 
origin  in  the  centre,  in  such  a  way  that  the  stimulation  of  the  latter 
amounts  to  much  the  same  thing  as  that  of  its  motor  or  inhibitory 
nerves  in  unfavourable  conditions.  The  only  legitimate  and  regular 
means  which  we  possess  of  causing  the  penetration  of  the  stimulus  into 
such  a  complex  arrangement  is  to  excite  one  of  the  nerves  or,  if  we  are 
able,  one  of  the  elements  which  come  to  it  and  whose  proper  function 
it  is  to  arouse  it  to  action  in  a  definite  manner. 

It  should  be  added,  however,  that,  when  the  so-called  centre  has  a 
certain  longitudinal  or  superficial  extent  (like  the  spinal  cord  or  the 
brain),  the  stimulus  may  be  propagated  from  the  locality  directly 


262  SYSTEMATIC    FUNCTIONS 

excited,  according  to  its  normal  laws,  to  other  portions,  in  such  a  way 
as  to  arouse  the  regular  play  of  the  system.  This  mode  of  stimulation 
may  be  made  use  of  in  order  to  analyse  the  system  under  consideration. 
It  is  not  contrary  to  the  rule  which  we  have  just  formulated,  of  which 
it  forms  a  particular  case. 

2.  Determination  of  reflex  centres. — This  is  what  physiologists 
have  clearly  understood,  so  far  as  it  concerns  the  centres  of  the  reflex 
actions  which  are  of  the  nature  of  those  arranged  in  series  throughout 
the  length  of  the  spinal  cord  and  the  medulla  oblongata.  The  action 
of  such  centres  is  defined  by  the  comparison  of  the  effects  produced  by 
stimulation  of  the  centripetal  and  the  centrifugal  nerves.  The  excitation 
of  the  centres  has  become  important  only  when  the  brain  has  been 
studied.  Here  it  is  a  question  of  surfaces  or  of  areas  rather  than  of 
centres.  Stimulation  of  a  portion  of  their  surface  amounts  to  the  same 
thing  as  to  cause  the  stimulus  to  penetrate  this  surface,  in  some  definite 
locality,  whence  it  is  transmitted  by  physiological  conduction  to  other 
portions.  It  may  then  manifest  certain  of  the  functional  associations 
which  are  effected  by  the  areas  known  as  centres.  These  associations 
could  not  be  manifested  in  their  integrity  ;  nor,  especially,  in  their 
regular  succession.     It  is  necessary  to  be  aware  of  this. 

B.  Stimulation  of  the  Posterior  Columns. ^This  has  been  effected 
in  the  frog,  the  rabbit,  the  dog  and  the  large  solipedia  \^dth  more  or 
less  success. 

1.  Total  effect. — The  irritation  of  the  posterior  medullary  columns 
by  pricking  causes  severe  jyain  and  violent  reflex  movements.  It  thus 
acts  in  the  same  way  as  irritation  of  the  posterior  roots,  and  this  is  not 
surprising  when  it  is  remembered  that  the  posterior  columns  of  the 
spinal  cord  are  in  great  part  formed  by  the  terminal  prolongations  of 
these  roots  themselves  which  follow  in  them  both  an  ascending  and 
descending  course  (this  latter  sometimes  very  long). 

Endogenous  and  exogenous  fibres. — But  in  spite  of  the  preponder- 
ating position  which  the  terminal  expansions  of  the  posterior  roots 
{exogenous  fibres)  occupy  in  them,  the  posterior  columns  of  the  cord 
contain  a  certain  number  of  special  fibres  {endogenous  fibres).  Taking 
origin  in  the  grey  matter  of  the  posterior  horns,  they  return  thither, 
having  formed  between  the  different  stages  of  this  matter  longitudinal 
commissures  of  relatively  short  length  comparable  to  those  which 
exist  in  the  fundamental  antero-lateral  columns.  These  endogenous 
fibres  present  this  remarkable  feature  that,  after  having  received  an 
impulse  by  their  dendrites  in  the  spongy  substance,  or  the  substance 
of  Rolando,  they  redistribute  it  in  two  opposite  directions,  the  one 
ascending,  the  other  descending,  by  means  of  a  bifurcation  of  their 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    263 


axon,  which  sends  one  branch  upwards  and  another  downwards,  both 
of  which  once  again  enter  the  grey  matter  of  the  spinal  cord.  The 
ascending  branches  form  a  tract  which  is  situated  in  the  anterior  or 
ventral  portions  of  the  cord  {ventral  tract,  cornu-commissural  zone,  field 
of  Westphal)  ;  the  descending  branches  form  a  tract  which,  according 
to  the  locality,  whether  dorsal,  lumbar,  or  sacral  in  which  it  is  investi- 
gated, assumes  the  aspect  of  a  comma,  of  a  tract,  of  an  oval,  or  of  a 
triangle. 

Isolated  excitation  of  the  endogenous  fibres. — What  is  the  result  of  an  excita- 
tion limited  to  the  endogenovis  fibres,  or  those  peculiar  to  the  posterior  cokunn  ? 
Wiiat  is  the  function  of  these  fibres  '?  But,  first  of  all,  what  means  is  available 
for  the  separate  stimulation  of  these  fibres,  to  the  exclusion  of  those  of  the  pos- 
terior  roots? 
Ph  ysiologists 
have  striven  to 
discover  such  a 
means  :  (1)  by  ex- 
peri  m  e  n  t  i  n  g  in 
the  interval  b  e  - 
tween  the  roots, 
at  a  point  as  far 
removed  as  possi- 
ble from  the  in- 
sertion of  these 
roots,  and  by 
making  use  for 
this  purpose  o  f 
large  animals 
(Chauveau)  ;  (2) 
by  suppressing  in 
a  radical  manner, 
bj"  the  supragang- 
lionic  section  of 
the  roots  and  the 
degener  ation 
which  is  a  conse- 
quence of  it,  the 
elements  of  these  roots  themselves  up  to  their  termination  (Gianuzzi). 


CereWlar  tract 
(tlechsig). 


Lat.  (crossed) 

pyramidal  tract 

(Flechsig). 


Goirer's  tract 


Direct  pyr.  tract  or 
Ant.  pyram. 

(Tiirck). 


Ground  bundle 
of  anterior 
column. 


Fig.   109. — Tracts  of  the  spinal  cord. 

Topography  of  the  tracts  in  the  cervical  region.  The  pyramidal  tract 
in  red,  the  cerebellar  in  blue. 


2.  Conclusion. — The  conclusion  which  must  be  drawn  from  these 
experiments  is  that  stimulation  of  the  posterior  columns,  independently 
of  the  radicular  elements  ivhich  they  contain,  gives  rise  in  the  animal  to 
manifestations  of  sensation,  either  painful  or  reflex.  This  is  the  con- 
clusion at  which,  with  the  exception  of  Van  Deen,  all  investigators 
have  arrived,  with  variations,  it  is  true,  in  the  results  obtained.  All 
are  equally  unanimous  in  maintaining  that  this  sensation  is  less  mani- 
fest than  that  which  results  from  stimulation  of  the  posterior  roots. 

CI.  Bernard,  operating  on  the  dog,  finds  the  maximum  sensitiveness 
behind,  near  to  the  median  hne  ;    Chauveau,  experimenting  on  the 


264 


SYSTEMATIC    FUNCTIONS 


Ist  dorsal  nerve 


solipedia,  finds  it  outside  this  locality  in  the  neighbourhood  of  the 
posterior  columns.  These  two  investigators  are  unanimous  in  main- 
taining a  great  difference  between  the  superficial  (very  sensitive)  por- 
tion and  the  deep  (almost  insensitive)  portion  of  the  posterior  columns 

All  that  has  been  furnished  by 
anatomy  since  these  observations  on 
the  constitution  of  these  columns  being 
taken  into  account,  it  is  certain  that 
these  observers  have  acted  most  fre- 
quently on  a  mixture,  in  variable  pro- 
portions, of  endogenous  and  exogenous 
fibres,  and  the  relative  insensibility  of 
certain  regions  is,  according  to  them, 
the  only  criterion  of  the  relative  pro- 
portion of  these  two  kinds  of  fibres  the 
existence  of  which  they  were  well  ac- 
quainted with,  but  without  knowing, 
as  is  now  well  known,  their  distribu- 
tion. On  the  other  hand,  the  experi- 
ments of  Gianuzzi  are  extremely  definite, 
they  teach  us  that  after  degeneration  of 
exogenous  fibres  of  radicular  nature,  there 
remain  in  the  posterior  columns  special 
or  endogenous  fibres  ivhose  excitation  still 
gives  rise,  in  the  absence  of  the  first,  to 
painful  manifestations. 


K 


■  Lumbar  nerves 


Sacral  nerve 


Fig.    110. — Structiu'e  of  the  column 
of  Goll  (Charpy). 

Posterior  aspect  of  the  spinal  cord 
On  the  left  the  column  of  Goll,  shaded 
On  the  right  the  diagram  shows  that  the 
column  of  Goll  is  formed  by  the  long 
fibres  of  the  posterior  roots,  and  that 
in  this  column  the  fibres  are  more 
internal  and  posterior  in  proportion 
as  they  come  from  below. 


Schiff,  after  having  cut  the  posterior  col- 
vimns  in  a  rabbit  under  the  influence  of 
ether,  detaches  them  from  the  anterior  por- 
tions of  the  spinal  cord  for  a  certain  distance 
in  the  direction  of  the  head  of  the  animal. 
These  colmnns  thus  detached,  but  still  con- 
nected with  the  spinal  cord,  are  subjected  to 
stimulation  (pinching)  at  their  free  extremity 
(as  would  be  done  on  a  sensory  nerve)  ; 
very  obvious  manifestations  of  pain  are  pro- 
voked, provided  that  the  stimulus  is  not 
distant  more  than  five  or  six  vertebrae 
from  the  point  where  the  columns  rejoin 
the  spinal  cord. 

This    experiment    should     no    longer    re- 


ceive the  interpretation  which  was  form- 
erly given  to  it.  Before  the  extremely  oblique  and  prolonged  course  of  the 
superior  bifurcated  branches  of  the  radicular  fibres  in  the  columns  of  Burdach  and 
of  Goll  was  known,  it  seemed  to  be  a  proof  at  the  same  time  of  the  existence  and  of 
the  sensitive  irritability  of  strictly  endogenous  fibres  (the  only  ones  considered  to 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    265 


run  such  a  long  course  in  the  direction  of  the  cokinuis).  It  is  now  evident,  on  the 
contrary,  that  what  are  excited  in  the  fasciculated  bands  thus  separated  from 
the  gi'ey  matter  for  a  considerable  length  are  principally  the  ascending  branches 
of  the  radicular  fibres  which  ha\-e  preserved  their  connexions  with  the  grey 
matter  at  the  upper  portion  of  the  tract  thus  separated.  The  endogenous  fibres 
must  therefore  only  participate  to  a  slight  degree  in  the  production  of  the  sensory 
phenomena  elicited  in  this  manner. 

Ascending  and  descending  sensory  paths. — Following  the  example  of  Schiff, 
Brown-Sequard  makes  a  section  of  the  posterior  column  and  detaches  this  column 
no  longer  above,  but  below  the  section  (over  a  lesser  length,  it  is  true).  The 
stimulation  of  this  colvimn  also  causes  pain  and  reflex  movements,  still  more 
intense,  according  to  Brown-Sequard,  than  those  which  are  elicited  in  the  experi- 
ment of  Schiff.  It  is  a  fact  well  established  by  a  niunber  of  physiologists  that 
an  excitation,  whether  made  above 
or  below  the  section  of  the  posterior 
columns,  or  of  the  entire  spinal 
cord,  with  or  without  separation 
of  the  posterior  columns  finds 
paths  both  descending  and  ascend- 
ing, by  which  it  can  proceed  to 
the  sensorivuii  and  give  rise  to 
conscious  or  unconscious  reactions 
which  prove  the  presence  of  sensi- 
bility. These  descending  paths, 
which  had  been  unravelled  b^• 
experiment,  anatomy  (which  had 
formerly  had  a  glimpse  of  them), 
now  demonstrates  in  an  obviovis 
manner  by  means  of  its  new 
methods  ;  there  are  also  descending 
branches  of  the  root  fibres  as  well 
as  equally  descending  branches  of 
the  endogenous  fibres,  which  dis- 
perse the  impulse  in  the  grey 
medullary  matter,  whether  above 
or  below  its  place  of  penetration, 
it  the  point  of  implantation  of 
the  dorsal  root. 


Fig.  111. — Collateral  ramifications  of  the  axis- 
cylinder  prolongations.  Sagittal  longitudinal 
section  of  the  spinal  cord  of  a  human  embryo 
of  20  centimetre?  (after  V.  Lenhossek). 

Rp,  fibres  of  the  posterior  roots  (central  prolonga- 
tions of  the  cells  of  the  spinal  ganglia)  ;  h,  their 
bifvu-cation  ;  Bu,  longitudinal  fibres  of  the  column 
of  Burdacli  ;  c,  collaterals  ;  t,  terminal  arborizations 
of  the  collaterals  enchng  in  the  proximity  of  the  cells 
of  the  grey  medullary  matter. 


3.  Direct  and  indirect  pro- 
longations of  the  sensory 
roots. — Thus  the  posterior 
columns  are,  on  the  one  hand, 
the  direct  continuation  of  the 
posterior  roots,  of  which  they  form  the  terminal  prolongations 
scattered  in  the  different  regions  of  the  grey  medullary  matter  ;  and, 
on  the  other  hand,  the  indirect  continuation  of  these  same  roots  after 
their  interruption  in  the  grey  matter.  In  other  words,  they  contain 
elements  of  the  first  order,  the  radicular  neurons,  and  elements  of  the 
second  order,  the  endogenous  neurons,  Avhich  receive  the  impulse  from 
the  first  and  enable  it  to  pass  over  another  stage.     It  is  interesting  to 


266 


SYSTEMATIC    FUNCTIONS 


.  -  C nihil. 


'■l.ML^ — - 


•i'rJ 


■V 


know,  by  means  of  physiological  experimentation,  that  the  artificial 
stimulation  of  these  neurons  gives  results  which,  if  not  identical,  are 
at  least  of  the  same  nature  as  those  which  are  caused  by  stimulation 
of  the  posterior  roots  themselves. 

Successive  stages  of  the  nerve  cycle  experimentally  selected  as  point  of  departure 
of  the  excitation. — The  nervous  system  is  comparable 
to  a  mechanism  whose  components  communicate  move- 
ment the  one  to  the  other  in  a  gradual  manner  and  in  a 
definite  direction.  Normally,  the  stimulus  which  acts 
upon  it  is  received  by  the  first  of  these  portions,  which  is 
obviously  constructed  in  such  a  manner  as  to  be  adapted 
for  its  reception.  But  if,  artificially,  it  is  communi- 
cated to  it  by  the  second  or  some  more  remote  series 
in  the  mechanism,  a  motor  effect  is  still  possible,  and 
this  is  what  experiment  clearly  proves  as  regards  the 
nervous  system.  Only,  on  account  of  the  multiplicity 
of  the  transmissions  and  the  variety  of  the  movement, 
and  of  the  complexity  of  the  connexions,  in  proportion 
as  the  initial  or  inotor  component  is  departed  from,  the 
resulting  effect  loses  its  norinal  character,  and  this 
in  any  circumstances  differs  from  that  which  results 
from  the  stimulus  acting  at  the  site  of  election.  And 
this  is  easily  understood  if  we  remember  that  at  each 
new  transmission  the  connexions  of  the  elements 
markedly  change. 

Determination  of  the  sensory  field. — If  we  eliminate 
the  nervous  system  as  a  whole  and  convey  the  im- 
pulsion to  the  muscles  themselves  or  to  their  motor 
nerves,  we  still  obtain  movement  ;  but  a  j^henomenon 
which  is  altogether  characteristic,  and  which  accom- 
panies it,  has  disappeared,  namely,  sensation.  To 
ascertain  what  field  the  sensory  phenomenon  occupies 
in  the  nervous  system,  what  systems  employ  it  for 
the  performance  of  their  particular  associated  func- 
tions, is  one  of  the  problems  with  which  we  are  con- 
fronted. 

The  experiments  which  precede  solve  this  problem 
to  a  limited  extent. 

They  prove  to  us  that,  tvhen  deprived  of  its  neurons 
of  the  first  order,  the  nervous  system  tvhen  it  is  stimulated 
is  still  capable  of  sensation,  the  field  in  which  is  con- 
tudinal  section,  that  of  the    tinned  the  excitation  provided  artificially  to  the  neurons 
middle    portion    being    the    of  the  second  order ,  being  still  capable  of  permitting 
its  development. 

Difference  of  the  effect  according  to  the  place  chosen 
in  the  cycle. — But  these  same  experiments  show  us 
also  that  the  sensory  effect  due  to  these  artificial  ex- 
citations is  quantitatively  less  than  that  which  results  from  the  stimulation  of 
the  sensory  roots.  And  perhaps  it  is  also  qualitatively  different  from  this  latter, 
because,  apart  from  the  pain  which  is  the  common  attribute  of  all  sensory  areas, 
it  is  impossible  for  us  to  ascertain  in  a  certain  manner  if  the  excitation  of  the 
endogenous  fibres  of  the  posterior  cokimns  supplies  to  the  animal  any  idea  of 
tactile  sensations  properly  so  called,  and  any  notion  of  position  in  s]mce. 


--  Descend  br. 


Fig. 


the 


112.— Cells    of 
spinal  column. 

Diagram  showing  the  three 
types  of  the  cells  of  the 
spinal      column     in      longi- 


ordinary  type.  The  grey 
and  white  tints  correspond 
to  the  two  matters  of  the 
spinal  cord. 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    267 


Paths  of  dispersion  of  the  impulses  in  the  sensory  field. — The  endogenous 
fibres  of  the  posterior  columns  are  indeed  a  continuation,  not  only  indirect,  bvit 
also  partial,  of  the  posterior  roots.  They  only  collect  a  portion  of  the  stimulus 
which  is  distributed  to  the  grey  matter  by  the  terminal  ramifications  of  the 
posterior  radicular  neurons.  The  rest  is  collected  by  other  fibres  forming  other 
columns  which,  in  the  spinal "  cord  itself,  build  up  formations  parallel  to  the 
posterior  columns.  These  are,  in  the  lateral  columns,  the  column  of  Oowers 
cmd  the  direct  cerebellar  tract. 

Remark. — In  the  conditions  which  are  imposed  on  experiment  for  the  laying 
bare     of     the     spinal 

cord  and  the  prepare-  Q^ 

tion  of  its  columns,  it 
may  indeed  be  asked 
if  the  sensibility  which 
these  coliimns  mani- 
fest (even  for  their 
own  fibres)  is  not 
quantit  a  t  i  v  e  1  y  ex- 
aggerated, as  happens 
in  similar  c  i  r  c  u  in- 
stances, for  all  parts 
artificially  exposed. 
Experiment  would 
thus  deceive  us  con- 
cerning the  real  value 
of  the  phenomenon 
which  it  serves  to 
render  evident. 

Cerebellar  tract — 
The  cerebellar  tract 
starts  from  Clarke's 
column  and  termin- 
ates in  the  cerebel- 
lum, in  the  grey 
matter  of  the 
vermis  superior.  Its 
ascending  direction 
may  be  ascertaineH 
from  the  results 
of  its  degeneration. 
This  tract  conveys  a  certain  portion  of  the  tactile  impulses  towards 
this  organ,  whose  function  is  still  very  enigmatical,  and  which,  as  re- 
gards the  general  consciousness  of  the  individual,  represents  a  special 
modification  of  consciousness  necessary  for  the  correct  performance 
of  certain  movements  or  co-ordinated  efforts. 

Subserving  more  especially  (as  is  shown  by  experiment)  the  function 
of  equilibrium,  the  cerebellum  co-ordinates  and  adjusts  the  movements 
by  which  this  function  is  carried  out  ;   and  it  can  only  do  this  in  pro- 


FiG.    113. — Ascending  and  descendine  cerebellar  neurons 
(after  M.  Duval). 

PR,  pons  ;  CE,  cerebellar  cortex  ;  AC,  reflex  cerebellar  arc; 
CL,  cell  of  Clarke's  column  ;  CP,  cell  of  Purkinje  ;  XS,  sensory 
nerve  ;    NM,  motor  nerve ;   AR,  reflex  medullary  arc. 


268 


SYSTEMATIC    FUNCTIONS 


Srd  cervical 


♦ 


1st  dors. . 


Cerv.  nucleus 


Cereb.  tract . 


12th  dorsal 


3rd  lumbar. 


Clarke 


portion  as  it  is  itself  at  every  moment  informed  concerning  the  attitude 
of  the  parts,  and  of  the  changes  in  this  attitude.  It  is  easy  to  under- 
stand, as  a  consequence  of  this  fact,  that  definite  relationship  between 
sensation  and  movement  is  present  in  it,  as  in  the  brain  ;  but  what 
especially   distinguishes    this   relation  from    that  in   the  brain  we  do 

not  know,  inasmuch  as  we  have  but 
little  information  concerning  the  exact 
nature  and  mechanism  of  the  functions 
of  both  of  these-  two  organs.  This 
tract  would  merit  the  appellation  of 
tract  of  Foville,  who  was  the  first  to 
ascertain  its  presence  in  the  new-born 
infant,  and  has  followed  it  up  to  the 
medulla  oblongata  and  the  cerebellum. 
Tract  of  Gowers. — The  ascending 
antero-lateral  tract,  called  tract  of  Goivers, 
has  another  destination  ;  it  proceeds, 
at  all  events  partially,  to  the  cerebral 
cortex.  Arising  in  the  commissural 
cells  of  the  posterior  horn,  its  fibres 
pass  from  one  side  to  the  other,  cross- 
ing one  another  ;  by  following  the  an- 
terior commissure,  they  then  pursue  a 
long  course  in  the  superficial  and  an- 
terior part  of  the  lateral  column,  reach 
the  medulla  oblongata,  where  they  en- 
counter a  nucleus  of  grey  rnatter,  which 
partly  interrupts  them,  and  finally  be- 
come united  with  the  fillet  or  ribbon 
of  Reil  (lemniscus)  running  j^arallel  to 
this  tract,  itself  also  of  sensory  origin, 
and  thus  reach  the  cerebral  cortex. 
Concerning  the  origins  of  this  tract  in 
the  spinal  cord  and  its  terminations  in 
the  encephalon,  there  are  some  differ- 
ences of  opinion  amongst  anatomists. 
The  tract  of  Gowers  sends,  through 
the  superior  cerebellar  peduncle,  fibres 
to  the  vermis  superior  of  the  cerebellum. 
It  has  thus,  partially,  the  distribution  of  the  direct  cerebellar  tract. 
Deep  lateral  tract  and  lateral  ground  bundle. — The  remainder  of 
the  lateral  column  is  occupied  by  two  fasciculations,  that  of  the  deep 


—  Sacral  michus 


Fig.  114.— The  column  of  Clarke 
and  the  direct  cerebellar  tract 
(after  Charpy). 

Relations  as  regards  situation  and 
size  of  Clarke's  column  (in  black  and  on 
the  right)  with  the  cerebellar  tract  (in 
blue  and  on  the  left). 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    269 


Fig.   115.     Clarke's  column  (Charpy). 


lateral  tract,  which  touches  the  grey  matter  posteriorly,  and  that  of 
the  so-caUed.  lateral  ground  bundle,  which  occupies  the  remainder  of 
the  space.  These  fasciculations  are  formed  of  commissural  fibres, 
which  unite  en  arc  the  different  stages  of  the  grey  medullary  matter. 

4.  Stimulation  of  the  lateral  column. — Experiments  have  been 
performed  on  the  lateral  columns 

just  as  on  the  posterior  and  an-  ciarke'scoiunn. 

terior  columns.     In  order  to  un-  "\ 

derstand   the   relation   of    these  /    ';' 

experiments,  and  at  the  same 
time  that  which  they  teach,  it  is 
necessary  to  remember  that,  for 
the  most  part,  they  date  from 
an  epoch  anterior  to  that  in 
which  the  sub-divisions  of  these 
different  tracts  into  partial  fas- 
ciculations, such  as  have  just 
been  pointed  out,  have  been  re- 
cognized through  the  study  of 
myelination  and  of  secondary  degenerations. 

At  the  same  time  the  three  columns  recognized  by  descriptive 
anatomy  (anterior,  lateral,  posterior)  were  defined,  but  in  reality  only 
two  of  these  were  distinguished  (the  antero-lateral  and  the  posterior). 
The  sensory  effects  of  stimulation  are  much  less  marked  in  the  lateral 
than  in  the  posterior  column. 

Since  the  first  recognition  of  these  details,  new  experiments  naturally  take 
into  accovmt  recent  advances  of  knowledge.  As,  on  the  other  hand,  the  great 
difficulty  is  to  experiment  separately  on  tracts  which  are  so  closely  approximated 
and  sometimes  mixed,  an  effort  has  been  made  to  utilize  the  fact  of  the  isolated 
and  successive  myelination  of  each  of  them,  in  order  to  investigate  them  separ- 
ately on  new-born  animals  in  different  stages  of  development.  If,  for  example, 
a  single  tract  is  myelinated  and  the  whole  responds  to  the  excitation,  it  follows 
tliat  the  resulting  effect  is  dependent  on  this  tract.  If,  on  the  other  hand,  a 
single  tract  is  deprived  of  myelin  and  the  result  anticipated  does  not  occur,  it  is 
because  this  result  appertains  to  a  non-myelinated  tract  (Bechterew).  It  is 
known  that  these  tracts  are  excitable  only  when  their  fibres  are  provided  with 
myelin,  that  is  to  say,  when  their  development  is  complete. 

Conscious  effects. — The  lateral  coliomn  has  therefore  been  completely  severed, 
and  its  superior  segment  has  been  stimulated  in  the  same  way  as  the  posterior 
colvimn.  A  certain  degree  of  sensibility  has  been  found  in  it,  but  less  than  in 
the  jDosterior  colimin  ;  this  is  explained  by  the  absence,  in  the  lateral  column, 
of  sensory  radicular  elements  which  (excepting  in  the  experiment  of  Gianiizzi) 
have  not  been  successfully  dissociated  from  the  endogenous  elements  in  the 
posterior  coltunn.  These  endogenous  elements  thus  manifest  in  a  still  more 
dtfinite  manner  the  weakness  of  their  sensory  effect. 

Reflex  effects. — The  reflex  effects  of  stimulation  of  the   lateral   columns   are 


270  SYSTEMATIC    FUNCTIONS 

like  the  conscious  results,  feebler  than  those  aroused  by  the  stimulation  of  the 
posterior  columns  in  the  neighbouring  or  corresponding  regions.  Yet'  these 
reflex  effects  are  very  definite  so  far  as  concerns  the  cardio-vascular  modifications. 
Dittmar,  who  has  studied  them,  observes  that  the  centripetal  stimulation  of 
the  lateral  columns  invariably  produces  them,  while  that  of  the  anterior  columns 
or  that  of  the  grey  matter  has  not  this  effect. 

According  to  Bechterew,  hemisection  of  the  cervical  spinal  cord  is  accompanied 
with  movements  of  rotation  and  circus  movements.  If,  further,  the  segment 
subjacent  to  the  section  in  the  region  which  corresponds  to  the  direct  cerebellar 
tract  be  irritated  in  the  newly  born  dog,  a  movement  of  the  trunk  is  elicited, 
the  latter  tiu-ning  slightly  on  its  axis,  and  of  the  head,  which  is  inclined  towards 
the  shoulder  of  the  same  side.  But  at  this  period  of  development  the  cerebellar 
tract  is  comjDletely  myelinated,  alongside  of  bundles  which  are  not  so,  or  are  so 
to  a  very  incomplete  degree.  The  effects  produced  by  the  excitation  would  thus 
be  due  to  the  myelination.  This  tract  would  therefore  be  a  conductor  of  the 
centripetal  impressions  which  govern  equilibration. 

The  antero-lateral  tract,  or  that  of  Gowers,  is  only  excitable  in  the  dog,  from 
the  second  or  fourth  day  after  birth.  Its  centripetal  stimulation  causes  reflex 
movements  of  the  trunk  and  of  the  thoracic  linabs.  As  other  centripetal  paths, 
equally  well  developed,  exist  at  that  time  in  the  same  region,  the  conclusion  to 
be  drawn  from  this  exjjeriment  is  less  precise.  It  may  be  maintained,  never- 
theless, with  considerable  probability  that  this  tract  forms  an  important  sensory 
path. 

C.  Section  of  the  Medullary  Teacts. — Another  method,  apphc- 
able  both  to  the  spinal  cord  and  nerves,  consists  in  making  hmited 
sections  of  the  grey  axis  of  the  cord,  or  of  its  tracts,  in  order  to  ascer- 
tain the  deficit  which  results  as  regards  certain  functions,  or  the  con- 
servation of  certain  others.  This  double  control  should  never  be  omitted 
in  experiments  on  the  nervous  system. 

1.  Hemisection  of  the  spinal  cord  ;  conservation  of  sensibility  in 
the  corresponding  portions. — When  made  on  one  side  only  of  the  spinal 
cord,  section  of  the  posterior  colurnns  does  not  abolish  sensation  in  the 
part  situated  below  this  section.  This  result  was  very  surprising  to  the 
old  experimenters,  who  regarded  the  spinal  cord  as  being  simply  an 
assemblage  of  the  peripheral  nerves  into  a  single  trunk  ;  it  was,  on 
the  contrary,  easily  understood  when  the  structure  of  this  organ  was 
unravelled,  and  more  especially  that  of  the  posterior  columns,  and 
especially  of  the  sensory  roots,  which  in  great  part  build  them  up. 
The  field  of  distribution  of  each  of  these  roots,  and  of  each  of  the 
elements  which  compose  them,  is  extremely  large,  thanks  to  the  rami- 
fications of  those  elements  which  are  distributed  both  above  and  below 
in  order  to  reach  the  grey  medullary  substance,  in  the  greater  portion 
of  its  extent.  Section  of  the  posterior  column,  above  the  lumbar  en- 
largement for  example,  produces  the  same  result  as  partial  interruption 
of  the  connexions  of  the  sensory  nerves  of  the  posterior  limbs  with  the 
grey  medullary  axis.     The  impulses  conveyed  from  the  skin  by  the 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    271 

posterior  roots  still  continue  to  flow  to  it,  by  more  liraited  paths  it  is 
true,  but,  nevertheless,  thej'  reach  the  sensorium.  Ought  it  to  be  con- 
cluded from  this  that  the  route  which  is  open  to  them  in  the  compli- 
cated system  consecutive  to  the  radicular  neurons  is  indeterminate, 
and  that  every  path  is  available  for  them,  provided  only  that  it  is  per- 
meable ?  Experiment  does  not  confirm  this,  and  such  a  supposition 
appears  to  be  inadmissible  from  every  point  of  view. 

In  the  system  which  they  help  to  form,  each  of  the  fasciculations, 
each  of  the  elements  which  we  consider  separately,  has  its  particular 
function,  up  to  a  certain  specific  point,  which  explains  why  if  an 
element  is  destroyed  or  interrupted  the  system  is  no  longer  balanced, 
but  is  to  a  certain  degree  thrown  out  of  equilibrium. 

This  is  what  seems  to  be  the  result  of  section  of  the  posterior  columns, 
with  the  exception  that  the  modification  produced  by  this  section,  as 
regards  the  exercise  of  sensation,  is  altogether  unexpected. 

Hyperaesthesia. — Fodera  was  the  first  to  observe  that,  after  section 
of  the  posterior  columns  of  the  spinal  cord,  not  only  is  sensation  not  abol- 
ished in  the  limbs  situated  below  the  point  of  section,  but  is  on  the  contrary 
exaggerated.  This  fact  has  since  that  time  been  re-examined  by  all 
investigators,  and  it  is  Brown-Sequard  who  has  studied  it  in  the  greatest 
detail.  According  to  this  author,  it  is  not  merely  sensibility  to  pain, 
but  all  modes  of  sensation  (to  heat,  to  cold,  to  pressure,  to  touch)  which 
are  thus  increased.  It  may  be  truly  said  that,  as  a  result  of  hyper- 
aesthesia, these  different  modes  of  sensation  are  easily  resolved  into 
pain. 

Reflex  sensibility  is  also  considerably  exaggerated.  Hyperaesthesia 
affects  all  the  known  forms  of  sensation. 

Crossed  anaesthesia. — Brown-Sequard  has  shown  that,  if  the  section 
is  made  on  one  of  the  two  posterior  columns  the  phenomenon  of  loss  of 
balance  of  sensation  assumes  a  new  form  :  there  is  hpyercesthesia  of 
the  corresponding  limb  and  hypocesthesia,  that  is  to  say,  incomplete 
anaesthesia,  of  the  limb  opposite  to  the  side  of  section .  This  is  known  as 
crossed  anaesthesia. 

According  to  Vulpian,  there  is  a  close  connexion,  a  sort  of  balance, 
between  these  two  phenomena,  the  one  of  exaggeration,  the  other  of 
diminution  of  sensation. 

Lesions  varied  as  regards  situation  and  extent. — In  short,  this  phenomenon 
ma3'  lie  elicited  by  lesions  whicli  are  ^■al•ied  both  as  regards  magnitude  and  situa- 
tion, but  always  on  the  condition  that  they  are  unilateral. 

The  most  simple  means,  because  it  requires  less  precision,  is  to  make  a  half 
section  of  the  spinal  cord  above  the  origin  of  the  nerves  corresponding  to  the 
region  whose  sensation  is  being  examined.  The  phenomenon  still  appears  if 
one  of  the  lateral  tracts  be  cut  in  the  region  approximating  the  posterior  column, 


272  SYSTEMATIC    FUNCTIONS 

or  if  the  postei'ior  horn  of  one  side  be  cut  (Brown-Sequard).  An  extremely 
hmited  disorder  of  one  side  of  the  cord  in  the  regions  indicated  suffices,  a  prick 
for  example. 

Persistence  of  the  effects. — On  the  condition  that  the  lesion  produced  persists, 
the  phenomenon  of  the  loss  of  balance  and  of  sensation  also  persists  for  weeks 
or  months  ;    in  the  case  of  irreparable  lesion,  it  appears  to  be  definite. 

It  may  be  equally  produced  by  lesions  situated,  no  longer  in  the  thickness 
but  in  the  height,  of  the  spinal  cord.  If  the  hemisection  is  made  in  the  cervical 
region,  there  is  very  marked  hypersesthesia  of  the  two  corresponding  limbs  and 
hyposesthesia  of  the  opposite  side.  If  it  is  made  near  the  medulla  oblongata, 
there  is  in  addition  hypersesthesia  of  the  ear  of  the  same  side  and  hyposesthesia 
of  the  opposite  ear. 

Action  on  the  region  situated  immediately  above. — Turck  and  Chauveau  have 
observed,  the  first  in  the  frog,  the  second  in  mammals,  that  an  incomplete  hemi- 
section of  the  cord  may  equally  cause  hypersesthesia  of  the  parts  situated  in 
front  of  the  lesion  of  the  same  side. 

A  hemisection  of  the  restiform  body,  or  of  the  anterior  (superior)  cerebellar 
peduncle,  of  the  cerebelliom,  or  of  the  corpora  quadrigemina,  causes  a  hyper- 
sesthesia of  all  corresponding  parts  of  the  body,  but  only  to  a  slight  extent. 

The  reaction  of  the  lesion  is,  as  is  obvious,  very  widespread  as  concerns  the 
sensory  regions  situated  behind  (in  man  below)  the  hemisection.  Whether  the 
lesion  be  a  complete  hemisection  or  a  destruction,  very  limited  in  thickness  and 
height,  or  of  the  posterior  column,  the  consequence  of  it  reacts,  not  on  any  sj^ecial 
limited  cutaneous  territory,  but  on  all  the  sensory  areas  situated  posteriorly,  in 
an  almost  vmiform  manner. 

2.  Explanation  :  decussation  of  the  sensory  paths. — The  crossed 
anaesthesia  which  follows  hemisection  of  the  spinal  cord  at  first  seemed 
to  be  very  easily  explained  by  an  intercrossing  of  the  conducting  fibres, 
which  was  effected  near  to  the  point  at  which  the  posterior  sensory 
roots  enter  the  spinal  cord.  This  opinion  was  held  by  Brown-Sequard, 
who  supported  it  by  the  following  observations  : — 

(a)  On  one  side  of  the  spinal  cord  (say  the  right)  a  hemisection  is  effected  above 
the  lumbar  enlargement,  and  the  ansesthesia  of  the  opposite  side  crossed  an- 
sesthesia)  which  is  the  consequence  of  it  is  determined  ;  then  hemisection  of  the 
cervical  cord  is  made  on  the  left  side  ;  the  consequence  of  this  would  be  an- 
sesthesia of  the  right  anterior  and  posterior  limbs,  which  had  at  first  not  merely 
preserved  their  sensibility,  but  were  hypersesthetic.  The  hemisection  in  both 
cases  involves  fibres  which  have  decussated  ;  the  dorsal  those  of  the  opposite 
portion  of  the  superior  limb  only  ;  the  cervical  those  of  the  anterior  limb  and  of 
the  posterior  limb  on  the  opposite  side  ;  in  this  way  the  animal  would  have 
three  limbs  paralysed  as  regards  sensation. 

(b)  The  two  halves  of  the  lumbar  enlargement  of  thesj^inal  cord  are  separated 
by  a  longitudinal  section  :  the  consequence  would  be  ansesthesia  of  the  two 
posterior  limbs,  as  if  their  sensory  elements  were  involved  at  their  point  of 
decussation. 

(c)  The  two  halves  of  the  cervical  enlargement  are  separated  by  a  longitudinal 
section  ;  the  consequence  would  be  ansesthesia  of  the  two  anterior  limbs,  but 
no  lesion  of  sensation  of  the  posterior  limbs  ;  the  section  here  would  involve 
the  site  of  decussation  of  the  sensory  elements  of  the  anterior  limb  onlj%  those 
of  the  posterior  limbs  having  already  decussated. 

Restrictions. — These  facts,  as  their  author  has  since  recogxiized,  have  neither 
the  general  application  nor  the  precision  which  would  be  desirable  if  they  are 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    273 

to  coiiJSrm  the  conclusion  which  in  the  first  instance  they  had  supported.  The 
crossed  anaesthesia  which  follows  hemisections  is  not,  it  must  be  remembered, 
ever  complete,  and  is  sometimes  little  marked.  In  the  bird,  this  hemisection  is 
followed  by  anaesthesia  of  the  same  side.  In  the  monkey,  the  anaesthesia  pro- 
duced by  hemisection  is  particularly  direct  (Mott).  In  the  frog,  hemisection 
induces  slight  hyperaesthesia  of  the  same  side  and  no  anaesthesia  of  the  opposite 
side.  Double  hemisection,  effected  at  different  heights,  permits  the  persistence 
of  sensation  in  all  the  limbs  ;  it  merely  diminishes  it.  Longitudinal  separation 
of  the  two  halves  of  the  lumbar  enlargement  also  merely  produces  a  diminution 
of  sensation  in  the  two  limbs. 

Lastly,  longitudinal  section  of  the  bracliial  enlargement  does  not  exert  an 
elective  action  on  the  anterior  limbs,  but  merely  produces  an  unequal  effect  on 
the  four  limbs,  more  markedly  on  the  anterior,  by  destrviction  of  the  grey  matter 
in  this  enlargement. 

The  following  fact,  due  to  Browai-Sequard,  must  be  mentioned.  In  a  rabbit 
a  hemisection  of  the  pons  is  made,  for  example,  on  the  left  :  anaesthesia  follows 
on  the  opposite  side  (on  the  I'ight)  and  hyperaesthesia  on  the  same  side  (on  the 
left).  Then  a  hemisection  on  the  spinal  cord  is  made  on  the  right  ;  inversion  of 
the  preceding  phenomena  results  ;  the  anaesthesia  passes  to  the  left  and  the 
hyperaesthesia  to  the  right. 

All  these  facts  show  that,  as  regards  the  development  of  sensation,  the  part 
played  by  the  spinal  cord  is  a  very  important  one,  but  it  is  a  part  which  at  the 
present  time  can  be  in  no  sense  defined.  Amongst  the  explanations  which  must 
be  rejected  should  be  placed  the  one  which  regards  the  elements  of  the  spinal 
cord  as  mere  conductors  transporting  to  the  brain  the  impulse  such  as  it  has  been 
received  by  the  sensory  nerves  of  the  skin. 

Partial  and  variable  crossing. — The  decussation  of  the  sensory 
tracts,  which  was  formerly  supposed  to  take  place  immediately  above 
the  point  at  which  the  posterior  roots  join  the  cord,  is  then  only  partial 
at  this  spot.  In  certain  species  of  animals  it  is  very  slight  ;  however, 
the  facts  detailed  above  show  that  it  is  real,  however  limited  it  may 
be. 

Anatomical  Data. — The  data  subsequently  supplied  by  anatomy  are 
in  complete  accord  with  the  results  of  these  experiments.  Amongst 
the  tracts  which  from  the  grey  axis  proceed  to  the  cerebral  cortex, 
we  observe  at  least  one,  the  antero-lateral  tract,  or  that  of  Gowers, 
whose  fibres  decussate  near  to  its  place  of  origin  in  Clarke's  column 
and  which  then  progresses  in  the  half  of  the  cord  opposite  to  that  in 
which  it  originated.  Another  crossing  of  the  sensory  elements,  more 
important  than  the  preceding,  occurs  in  the  meduUa  oblongata,  in  the 
immediate  vicinity  of  that  of  the  motor  elements  of  the  pyramidal 
tracts.  The  ascending  branches  of  the  radicular  neurons,  after  having 
ascended  in  the  posterior  columns  as  far  as  the  union  of  the  spinal  cord 
and  of  the  medulla  oblongata,  while  giving  off  in  this  course  numerous 
collaterals  in  the  grey  medullary  axis,  exhaust  their  last  ramifications 
in  two  nuclei  (nuclei  of  Goll  and  of  Burdach)  which  are  the  origins  of 
a  very  important  sensory  tract,  the  fillet  or  lemniscus  (ruban  de  Reil). 

p.  T 


274  SYSTEMATIC    FUNCTIONS 

It  is  the  fillet  itself  which  decussates  near  to  its  origin  ;  shortly  after 
its  decussation,  it  joins  on  to  the  tract  of  Gowers,  increases  in  size  by 
the  acquisition  of  the  sensory  elements  coming  from  the  bulbar  nerves, 
and,  thus  constituted,  proceeds  towards  the  central  convolutions  of 
the  cerebral  cortex,  not  without  presenting  during  its  course  an,  at  all 
events,  partial  relay  in  the  optic  thalamus. 

Unilaterality  or  bilaterality  of  sensory  representations. — The  whole 
cutaneous  surface  of  one  side  of  the  body  should  thus  have,  in  a  certain 
sense,  its  sensory  representation  in  the  cortex  of  the  opposite  hemi- 
sphere ;  no  doubt  existed  on  this  point  until  lately,  and  this  view  is 
generally  maintained  ;  but  the  example  of  the  sense  of  sight,  in  which 
the  decussation  is  only  partial  ;  that  of  the  motor  apparatus,  in  which 
the  same  side  of  the  brain  acts,  although  very  unequally,  on  the  muscles 
of  both  sides  of  the  body,  should  lead  to  caution  being  exercised  in 
this  matter,  and  the  more  so  because  no  means  exists  of  absolutely 
controlling  an  entire  and  perfect  decussation. 

Galvanometric  method. — Tlie  ti'ansmission  of  the  impulse  is  accompanied,  as 
is  well  known,  by  electro-motor  phenomena  (negative  variation  or  current  of 
action)  which  are  rendered  evident  and  are  measured  by  the  galvanometer. 
Gotsh  and  Horsley  have  observed  that,  on  stimulating  the  sciatic  nerve  of  one 
side,  currents  of  this  kind  are  developed  in  the  lumbar  segment  of  the  spinal  cord, 
these  currents  obivously  accompanying  the  propagation  of  the  impulse  tlirough 
this  segment.  But  though  these  currents  exist  on  both  sides,  yet  they  are  always 
more  intense  on  the  side  of  the  stimulation. 

Syndrome  of  Brown-Sequard. — This  name  is  given  to  a  collection  of 
symptoms  consisting,  as  the  result  of  unilateral  lesion  of  the  spinal 
cord  of  motor  paralysis  of  the  one  side  combined  with  anoisthesia  of  the 
opposite  side  (with  or  without  hypersesthesia  on  the  side  of  the  lesion). 
This  association  of  symptoms  recalls  that  which  is  experimentally 
effected  by  hemisection  of  the  spinal  cord.  The  combinations  of 
anaesthesia  and  of  hypersesthesia  may  here  also  be  very  variously 
displayed. 

3.  Medullary  sensory  paths  of  the  deep  organs. — The  evidences 
which  are  most  often  brought  forward  as  a  proof  of  sensory  manifesta- 
tions are  the  defensive  reactions  of  animals  which  are  performed  by 
the  muscles  of  the  skeleton  ;  but  certain  movements  of  the  deep  organs, 
connected  with  the  functions  of  organic  life,  may  equally  serve  as 
very  sensitive  aesthesiometers.  Miescher  has  performed  experiments 
of  this  kind  by  registering  the  carotid  pressure  in  a  curarised  rabbit, 
and  by  noting  the  variations  which  it  undergoes  as  the  result  of  stimu- 
lation of  the  sciatic  nerve,  both  in  the  normal  condition  and  when  the 
spinal  cord  is  incompletely  divided,  the  section  being  performed  above 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    275 

the  origins  of  this  nerve.  By  making  limited  sections  of  the  two  lateral 
columns,  and  by  proceeding  to  the  point  in  which  they  meet  in  the 
thickness  of  the  cord,  the  transmission  of  the  impulse  to  the  vaso- 
motor centres  was  almost  entirely  suppressed.  Conversely,  if  the 
whole  cord  be  divided,  with  the  exception  of  one  of  the  lateral  columns, 
stimulation  of  the  sciatic  nerve  on  the  opposite  side  caused  the  pressure 
to  rise  almost  as  much  as  in  the  normal  animal  ;  stimulation  of  the 
sciatic  on  the  same  side  was  nearly  without  result.  The  author  has 
concluded  that  the  site  of  the  passage  of  the  impulse  thus  made  on 
the  nerve  of  the  inferior  extremity  is  chiefly  in  the  lateral  column  ; 
that,  further,  this  transmission  is  effected  by  paths,  some  of  which  are 
direct,  but  the  majority  crossed. 

It  must  be  remembered  that  the  lateral  colmnn  is  formed  of  longer  tracts 
situated  more  superficially,  and  of  shorter  or  commissural  tracts  arranged  longi- 
tudinally adjacent  to  the  grey  matter.  In  physiological  researches  it  is  at  pre- 
sent necessary  to  give  up  the  attempt  to  operate  in  a  separate  manner  on  these 
different  fasciculations  ;  as  the  difficulty  of  isolating  the  one  from  the  other  is 
very  great,  and  still  more  so  that  of  isolating  the  three  fundamental  columns 
of  the  cord  which  are  visible  to  the  naked  eye  from  the  grey  matter. 

In  the  anterior  columns  physiological  experimentation  does  not  enable  us  to 
recognize,  any  more  than  do  the  results  furnished  by  anatomy,  any  element 
-whose  direction  is  ascending,  in  other  words,  a  so-called  sensory  element. 

4.  Important  part  played  by  the  grey  matter  in  the  transmission 
of  sensory  impressions. — A  fact  which  has  also  been  demonstrated  by 
physiology,  before  anatomy  proved  it  to  be  true,  is  the  importance  of 
the  grey  matter  in  the  transmission  of  sensory  impulses  through  the 
tissue  of  the  spinal  cord  in  order  to  reach  the  brain.  That,  individually, 
the  posterior  columns  and  a  portion  of  the  lateral  columns  take  an 
obvious  part  in  this  transmission  is  easily  understood  from  the  experi- 
ments which  have  been  described  above  ;  but,  without  the  co-opera- 
tion of  the  grey  matter,  it  would  be  impossible  for  these  structures  to 
ensure  the  exercise  of  sensation.  This  is  proved  by  the  following 
experiment  : 

Experiment. — The  whole  thickness  of  the  spinal  cord  is  cut,  with 
the  exception  of  the  posterior  columns  ;  sensation  is  abolished  in  the 
subjacent  regions  ;  even  if,  with  the  posterior  columns  the  lateral 
columns  are  permitted  to  remain,  when  the  rest  of  the  cord  is  cut, 
sensation  disappears.  This  is  because  the  medullary  grey  matter  plays 
a  paramount  part  in  the  sensory  functions  and  its  section,  by  itself 
alone,  completely  annuls  the  functional  activity  of  the  tactile  sensory 
system.  This  role  would  be  demonstrated  better  and  more  clearly  if 
it  were  possible  to  separately  destroy  the  grey  matter  for  a  certain 
length,  all  the  columns  being  left  intact  ;    but  its  central  situation 


276  SYSTEMATIC    FUNCTIONS 

prevents  its  isolated  destruction.  We  are  reduced  to  cutting  it  con- 
jointly, sometimes  with  one  column,  sometimes  with  another.  It  is 
only  observed  (and  investigators  are  unanimous  on  this  point)  that  an 
isolated  section,  or  one  combining  that  of  the  different  columns,  has  no 
marked  and  complete  ancesthetic  action  so  long  as  the  grey  matter  has 
not  been  divided  throughout  its  thickness. 

This  may  be  said  at  least  as  regards  the  sensation  of  pain,  because 
some  would  make  reserves  concerning  certain  forms  of  sensation  for 
which  they  consider  that  separate  paths  exist.  More  especially  would 
tactile  sensation  have,  in  the  posterior  columns,  its  conducting  fibres 
distinct  from  those  which  transmit  painful  impressions  (Schiff),  but 
the  fact  is  disputed. 

Situation  of  the  grey  matter  intercalated  in  the  course  of  the  impulses. — When 
it  is  remembered  that  the  grey  substance  of  the  spinal  cord  is  the  locality  in  which 
the  radicular  neurons,  or  those  of  the  first  order,  come  into  contact  with  those 
of  the  second  order,  which  conduct  it  towards  the  brain,  and  that  it  is  hence 
a  compulsory  halting-place  for  the  current  of  excitation  which  traverses  the 
system  of  tactile  sensation,  the  results  fi.u'nished  by  experiment  and  the  essential 
part  which  the  latter  attributes  to  it  in  the  functions  of  this  system  will  cause 
the  less  siu'prise.  Doubtless  the  current  of  excitation  follows  the  conducting 
fibres,  both  of  the  first  and  second  order,  but,  to  pass  from  one  to  the  other,  it 
cannot  avoid  the  grey  matter.  Every  serious  lesion  of  the  latter  may  thus 
destroy  sensation. 

Paradox. — Yet  it  is  difficult  to  exjDlain,  even  with  these  data,  how  a  transverse 
section  of  this  grey  matter,  provided  that  it  is  complete,  suffices  to  entirely  abolish 
sensation  in  the  regions  posterior  to  it.  It  is  surprising  to  observe  that  the  in- 
terruption of  this  feltwork  in  one  point  has  so  decided  an  effect,  resembling  that 
of  section  of  a  band  of  parallel  fibres.  It  is  still  more  surprising  to  note  that 
authors  like  Vulpian,  who  have  studied  this  subject  with  the  greatest  attention 
and  with  scrupulous  conscientiousness,  affirm  that  a  series  of  sections  carried 
out  in  different  direct  ons,  but  incompleteh',  allows,  on  the  contrary,  sensation 
to  persist ;  as  if  the  impulses,  which  come  from  the  posterior  roots,  could  have 
in  this  grey  matter  an  indeterminate  course,  an  always  possible  means  of  flowing, 
on  the  one  condition,  that  the  continuity  of  the  grey  axis  is  not  interrupted. 

Lastly,  and  this  is  a  no  less  astonishing  fact,  after  these  incomplete  sections 
carried  out  in  different  directions,  the  animal  still  recognizes  the  site  of  the  im- 
pression and  turns  to  the  side  of  the  limb  which  is  being  irritated  (Vulpian). 

Remarks.— These  facts  suggest  two  remarks,  already  made  by  the  authors 
of  these  experiments,  and  which  it  is  advisable  to  refer  to,  namely  :  that 
experimental  attempts  to  act  ;'n  an  isolated  manner  on  such  and  such  a  portion 
of  the  spinal  cord  are  extremely  delicate  and  liable  to  error  ;  and  secondly,  that 
the  sensation  displayed  in  these  experiments  is  almost  exclusively  that  of  pain, 
and  that  the  conditions  of  its  production  are  more  general  and  may  be  considered 
as  less  precise  than  those  of  other  forms  of  sensibility. 

2.   Motility  in  the  Spinal  Cord 

From  the  spinal  cord  proceed  motor  nerves  which  are  distributed 
to  most  of  the  muscles  of  the  body.    These  nerves  represent  the  terminal 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    277 

neurons  of  the  tactile  system  ;  they  convey  to  the  muscles  the  impulse 
which  they  have  themselves  received  in  the  spinal  cord. 

Multiple  internal  sources  of  motor  excitation. — This  excitation 
comes  to  them  by  somewhat  varied  routes,  namely  :  (1)  certain  simple 
reflexes,  directly  from  the  sensory  roots  ;  (2)  more  complicated  reflexes 
of  the  grey  ganglionic  nuclei  arranged  in  series  in  the  cord,  the  medulla 
and  the  base  of  the  brain  ;  (3)  conscious  voluntary  acts  of  the  cerebral 
cortex.  It  must  not  be  forgotten  that  the  common  source  of  these 
stimuli  is  invariably  in  the  sensory  roots  and  the  sensorial  apparatus 
situated  at  their  extremity.  But  this  transmission,  which  is  immediate 
and  approximate  for  the  execution  of  the  reflex  acts,  is,  on  the  con- 
trary, mediate,  and  so  much  the  more  remote  in  proportion  as  it  is  a 
question  of  acts  and  of  functions  concerning  instinct,  and,  above  all, 
intelligence  ;  the  more  these  functions  assume  a  psychical  aspect,  so 
much  the  longer  is  the  duration  of  the  impulse  in  the  nervous  system, 
the  more  complicated  is  the  course  which  it  runs  in  it,  the  more  round- 
about and  prolonged  are  the  paths,  Avhich,  by  compelling  it  to  pass 
through  the  cortex,  bring  it  back  to  the  motor  nuclei  of  the  spinal 
cord. 

Motor  Field. — Just  a;^,  by  comparison  with  the  neurons  of  the  jDosterior  roots, 
those  neurons  are  called  sensory  wliich  proceed  from  the  cord  to  the  encephalon, 
so  by  comparison  w  ith  the  neurons  of  the  anterior  roots,  those  neiu-ons  are  called 
motor  which  descend  from  the  brain  towards  the  sjainal  cord  and  the  medulla 
oblongata. 

That  which  distinguishes  both  of  them  from  the  strictly  sensory  and  motor 
nerves  is,  as  regards  the  first,  that  they  no  longer  receive  the  impiilse  directly 
from  the  exterior  ;  as  regards  the  second,  that  they  no  longer  directly  transmit 
it  to  the  organs  of  movement,  btit  only  by  the  obligatory  intermediation  of  the 
nerves  of  the  primary  or  inferior  system.  The  first  are  nerves  stimulated  by 
nerves,  and  they  react  according  to  their  natixre  and  theii*  organization  ;  the 
second  are  nerves  which  stimulate  nerves  and  equally  make  use  of  the  organiza- 
tion of  the  latter,  and  no  longer,  like  them,  simj^ly  of  muscular  activity.  The 
difference  of  the  effects  in  the  two  cases  results  jDrecisely  from  the  transformations 
which  take  place  in  the  transmission,  from  the  fact  of  this  organization  w^iose 
existence  they  reveal  to  us,  if  not  its  internal  details. 

Cerebro-spinal  motor  tracts — Pyramidal  tract. — Of  these  descending  tracts 
the  best  known  is  that  wliich  forms  the  so-called  pyramidal  tract.  It  takes  its 
origin  in  the  central  convolutions.  Its  fibres,  mixed  at  first  with  those  of  the 
corona  radiata,  then  proceed  by  the  internal  capsule,  follow  the  crusta  (pes)  of 
the  crus  cerebri,  pass  through  the  pons  varolii,  partially  decussate  in  the  medulla 
oblongata,  of  which  they  form  the  so-called  antero-pyramidal  tract  ;  the  portion 
which  does  not  decussate  follows  the  anterior  tract  of  the  cord  of  the  same  side, 
while  the  decussated  portion,  which  is  much  more  important,  accompanies  the 
posterior  portion  of  the  lateral  column,  in  which  it  forms  a  well-marked  fascicu- 
lation.  The  crossed  pyramidal  tract  extends  to  the  fourth  pair  of  sacral  nerves  ; 
the  direct  pyramided  tract  to  the  first  lumbar  (Dejerine  and  Thomas).  Such  is 
the  arrangement  in  n^ian. 

In    animals  there  is  also  a  crossed  pyramidal  tract  which  accompanies  the 


278 


SYSTEMATIC    FUNCTIONS 


lateral  column  of  the  cord,  but  the  direct  tract  is  not  differentiated  as  it  is  in 

man,  and  does  not  proceed  through  the  anterior  column  ;    it  is  represented  by 

fibres  which  follow  the  lateral  column  of  the  same  side,  being  more  or  less  mixed 

with  the  crossed  fibres  coming  from  the  opposite  side.     In  man  an  arrangement 

of  this  kind  is  sometimes  present  without  interfering  with  the  column  of  Tiirck 

which  accompanies  the  anterior  column.     The  decussation  of  the  motor  tracts 

undergoes  very  great  variations  according  to  the  species,  and  even  in  different 

individuals  of  the  same  species. 

Other  descending  paths. — Ground  bundles. — In  addition  to  these  descending 

fibres  of  variable  length,  which  form  such  a  remarkable  commissure  between  the 

cerebral     cortex    and    the    grey 

medullary  axis,  there  are  others 
Post.  root.  ,  .  ^         "^ .  '  •         <• 

which  unite  to  the  grey  axis  of 

the    spinal  cord  either  the  gan- 
glia of  the  base  of  the  brain,  or 


Fig.    116. — The  short  paths  of  the  spinal  cord. 
They   are   grouped   around   the  grey   matter  ;    the 
-white  field  corresponds  to  the  middle  or  long  paths. 


117. — Descending 
fibres. 


cerebellar 


Lumbar  spinal  cord  ;  fibres  of  the 
column  and  anterior  roots  degenerated 
after  extirpation  of  tlie  cerebellum 
(Marchi). 

other  parts  of  this  axis  itself.  Like  the  ascending  fibres,  the  descending  cerebro- 
spinal fibres  are  of  very  variable  length  and  form  an  infinite  number  of  con- 
nexions, of  which  we  clearly  recognize  only  the  most  striking. 

The  shortest  commissural  fibres  are,  as  usual,  those  which  directly  approxi- 
mate the  grey  matter,  over  which  they  are  arched,  like  bridges  of  different  lengths. 

Yet  further,  an  important  formation  in  the  ground  bundle,  the  posterior  longi- 
tudinal bundle,  is  to  be  noted,  as  it  will  be  necessary  to  revert  to  it  more  than 
once. 

Cerebello-spinal  motor  paths— Antero-pyramidal  tract.— As  is  implied  by  its 
name,  this  tract  is  situated  at  the  surface  of  the  cord,  at  the  periphery  of  the 
anterior  and  slightly  of  the  lateral  column. 

As  it  descends  it  approaches  the  mecUan  line  of  the  anterior  fissure,  which  it 
soon  skirts.  The  process  of  degeneration  proves  it  to  be  a  descending  tract, 
formerly  called  motor  (Lowentlial).  It  is  a  centrifugal  cerebellar  tract  ;  it  de- 
generates after  unilateral  ablation  of  the  cerebellum  (Marchi)  and  after  section 
of  the  inferior  cerebellar  i^eduncle  (Basilewski).  Helweg,  Bechterew  described 
yet  another  tract  under  the  name  of  periolivary  or  olivary  tract  ;  it  is  a  small 
superficially  situated  tract,  which  would  connect  the  olivary  body  with  the  dif- 
ferent stages  of  the  grey  medullary  axis,  and  would  be  attached  to  the  system 
of  the  cerebello-spinal  connexions.  The  motor  fibres  taking  origin  in  the  cere- 
bellum are  not  fixed  in  these  more  or  less  defined  and  recognizable  formations, 
but  are  disseminated  as  far  as  the  crossed  pyramidal  tract.  These  are  those 
which  are  found  to  be  degenerated  in  it  after  ablation  of  the  cerebellum  or  sec- 


CONSCIOUS    AND  UNCONSCIOUS  :    THEIR  SEPARATION    279 

tion  of  the  inferior  honiolateral  cerebellar  peduncle.     A  tract  called  intermediate 
has  also  been  defined. 

The  motor  cerebello-spinal  tracts  are  thus,  as  is  obvious,  the  counterpart  of 
the  sensory  spino-cerebellar  tracts.  Both  provide  between  the  cerebellum  and 
the  spinal  cord  a  double  current  of  impulses.  The  nervous  cycle  of  which  they 
form  part  thus  supplies  a  particular  form  of  the  co-ordination  of  movements, 
equilibration.  The  elements  of  this  cyclic  system  are,  as  will  be  seen  further 
on,  chiefly  organized  in  the  cerebellum. 

1.  Stimulation  of  the  descending  tracts. — The  different  tracts  of 
the  spinal  cord  have  been  stimulated  in  their  normal  condition,  or 
after  isolated  section  and  separation  of  the  neighbouring  parts,  in 
order  to  act  upon  them  in  the  same  way  as  upon  ordinary  nerves.  In 
this  way  either  the  anterior  or  lateral  tracts  have  been  stimulated. 

Preliminary  question. — As  regards  all  these  descending  tracts,  from 
the  very  commencement  of  investigation,  the  same  question  has  arisen 
as  in  the  case  of  the  ascending  tracts. 

How  are  the  strictly  motor  elements  of  the  spinal  cord  (the  endo- 
genous fibres)  to  be  distinguished  from  the  strictly  radicular  motor 
elements  which  arise  in  it  from  the  anterior  horns  of  the  grey  matter  ? 
Separate  excitation  of  both  is  here  much  easier  than  in  the  case  of  the 
ascending  elements.  The  field  of  origin  of  the  motor  radicular  neuron 
has  not,  in  the  spinal  cord,  the  same  extension  as  the  field  of  distribu- 
tion of  the  sensory  radicular  neuron  in  its  posterior  portion.  Instead 
of  those  bifurcations  which,  in  the  tracts  of  Goll  and  of  Burdach  follow 
such  a  wide  course,  the  radicular  neuron  traverses  the  antero-lateral 
tract  perpendicularly  to  its  fibres,  in  such  a  manner  that  between  the 
two  anterior  roots  it  is  the  special  fibres  of  the  spinal  cord  which  are 
observed. 

Apparent  contradictions. — By  stimulating  the  anterior  columns  in 
the  interval  between  the  roots,  after  or  without  previous  section  of 
the  spinal  cord  or  of  these  tracts,  Longet  has  determined  their  excita- 
bility and  their  motor  function.  This  result  was  then  interpreted  as 
implying  a  direct  continuity  between  the  columns  and  the  anterior 
roots.  Chauveau,  on  the  contrary,  experimenting  on  large  animals, 
arrived  at  the  conclusion  that  these  columns  are  inexcitable.  Like 
Longet,  he  makes  use  of  electrical  excitation  ;  but,  absorbed  in  avoid- 
ing its  diffusion  to  the  neighbouring  motor  roots,  he  graduates  it  care- 
fully and  maintains  it  at  an  intensity  sufficient  to  stimulate  the  motor 
roots.  He  thus  observes  that  the  stimulus  which  arouses  the  functions 
of  these  latter  does  not  produce  any  motor  effect  when  it  is  applied  to 
the  columns  in  the  interval  between  the  roots.  And  this  is  the  reason 
why  he  declines  to  admit  the  motor  excitability  of  these  columns. 

2.   Decisive   experiment. — Vulpian  has   devised  an   experiment   on 


280  SYSTEMATIC    FUNCTIONS 

this  disputed  point  which  is  decisive.  In  a  rabbit  or  a  dog,  after  it 
has  been  put  under  the  influence  of  ether,  he  lays  bare  the  spinal  cord 
for  a  length  of  six  to  ten  centimetres  above  its  lumbar  enlargement  ; 
he  cuts  all  the  roots  which  correspond  to  this  length  (in  order  that  he 
may  not  have  to  take  into  account  the  movements  which  would  result 
from  their  stimulation  by  the  diffusion  of  the  stimulating  current). 
He  cuts  the  cord  in  the  most  anterior  portion  of  the  region  which  has 
been  laid  bare  and,  throughout  the  extent  of  the  latter,  removes  the 
posterior  columns,  a  portion  of  the  lateral  columns,  and  as  much  as 
possible  of  the  grey  matter,  in  such  a  way  that  the  anterior  or  antero- 
lateral columns  (according  to  circumstances)  thus  separated  are  only 
connected  with  the  cord  by  their  posterior  extremity.  If  the  anterior 
extremity  of  the  columns  isolated  in  this  way  be  pricked  or  compressed, 
somersaults  are  provoked ;  that  is  to  say,  contractions  of  the  muscles 
of  the  hindquarters  of  the  animal  and  movements  of  the  tail.  If,  by 
following  the  anterior  fissure,  the  two  anterior  columns  be  separated 
with  exactitude  the  one  from  the  other  by  a  longitudinal  incision,  it  is 
observed,  by  stimulating  one  of  them,  that  much  stronger  movements 
ensue  in  the  corresponding  limb  than  in  the  limb  of  the  opposite  side. 

In  the  newborn  dog,  the  pyramidal  tract  is  not  yet  myelinated.  Stimulation 
of  the  lateral  columns,  when  made  at  this  period  of  development,  does  not  pro- 
duce the  motor  effects  which  ensue  in  the  adult,  or  only  from  the  epoch  of  the 
complete  develoj^ment  of  these  parts  (Bechterew). 

Chiefly  direct  and  partially  crossed  effects. — There  is  thus  no  doubt 
that  stimulation  of  the  anterior  columns,  and  also  that  of  the  lateral 
columns,  is  followed  by  motor  reactions  attributable  to  this  very  stimu- 
lation. Further,  this  experiment  shows  us  that  the  transmission  of 
the  impulse  from  these  tracts  to  the  motor  nerves  of  the  anterior  roots 
is  effected  (in  the  grey  medullary  matter)  chiefly  on  the  corresponding 
side,  and  subordinately  on  the  opposite  side  ;  in  other  words,  that  it 
is  chiefly  direct  and  very  partially  crossed. 

3.  Quantitative  difference. — The  experiments  of  Chauveau  have 
nevertheless  a  very  important  bearing.  If,  indeed,  we  ought  to  modify 
the  formula  in  which  his  conclusion  is  expressed  and  maintain  with 
Vulpian  and  Longet  the  motor  excitability  of  the  antero-lateral  columns 
of  the  spinal  cord,  we  see  from  these  same  experiments  (as  also  from 
that  of  Vulpian)  that,  jro7n  the  quantitative  point  of  vieiv,  if  not  from 
the  qualitative,  there  is  a  great  difference  in  the  excitability  of  the  motor 
roots  and  of  the  antero-lateral  columns,  and  this  proves  to  us  that,  if 
these  two  formations  participate  in  the  same  general  function,  that  of 
motricity,  functional  differences  exist  between  them  by  which  they 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    281 

can  be  experimentally  distinguished.  In  reality,  these  two  formations 
are  not  the  immediate  prolongation,  the  one  of  the  other,  but  are 
mutually  connected  by  the  grey  matter,  which,  by  establishing 
their  connexions,  transforms  the  current  of  excitation  which  passes 
through  it. 

Direct  tract  and  crossed  tract. — Stimulation  of  the  anterior  column 
is  followed  by  undeniable  motor  results  ;  that  of  the  lateral  columns 
is  equally  so.  But  these  columns  are  complex  formations  and,  further, 
they  are  not  absolutely  equivalent  in  man  and  in  animals. 

We  leave  on  one  side  the  ascending  fibres  which  are  present  in  the 
lateral  column  and  which  are  excluded  from  the  stimulation  (as  here 
practised)  by  the  direction  of  their  conduction.  The  anterior  column 
contains  the  direct  portion  of  the  pyramidal  tract,  the  lateral  column 
contains  that  portion  of  it  which  has  decussated  in  the  bulbar  pyramids. 
But,  in  both  columns,  to  the  tract  known  as  the  pyramidal  another 
one  is  added,  the  ground  bundle,  formed  of  more  or  less  lengthy  com- 
missural fibres  which  connect  the  superposed  stages  of  the  grey  axis. 
At  all  events  this  is  the  arrangement  in  man  ;  in  animals  the  direct 
tract  is  almost  completely  wanting,  and  its  elements  are  traced  back 
to  the  lateral  column  of  the  same  side.  Experimental  stimulation 
performed  in  animals,  when  it  is  applied  to  the  anterior  tract,  thus 
chiefly  affects  the  commissural  fibres,  and  consequently  renders  evident 
their  motor  function  ;  when  it  is  applied  to  the  lateral  column,  it  affects, 
on  the  contrary,  a  collection  of  fibres  in  which  the  pyramidal  tract 
occupies  a  prominent  place  from  the  motor  point  of  view. 

4.  Section  of  the  antero-lateral  columns. — As  the  result  of  a  large 
number  of  experiments  made  by  different  observers,  it  may  be  con- 
cluded that  section  of  the  antero-lateral  columns  paralyses  the  movement 
of  the  subjacent  7nuscles.  Thus  it  consequently  interrupts  the  trans- 
mission of  the  impulses  which  descend  from  the  superior  regions  of 
the  nervous  system,  and  only  suffers  the  continuance  of  the  most  simple 
reflexes. 

Section  of  the  whole  cord  with  the  exception  of  the  Antero-lateral 
Columns. — If,  conversdy,  the  whole  cord  with  the  exception  of  the 
antero-lateral  columns  be  cut  (for  example,  a  little  above  the  lumbar 
enlargement),  movement  is  preserved  in  the  subjacent  members,  and 
this  is  the  counter  proof  of  the  preceding  experiment,  to  the  truth  of 
w^hich  it  bears  witness.  The  movements  which  are  thus  preserved  are 
not  all  capable  of  the  same  interpretation  ;  some  are  voluntary,  and 
proceed  from  the  impulses  starting  in  the  cerebral  cortex  ;  others  are 
emotiojial,  and  proceed  from  the  optic  thalamus  ;  others,  again,  are 
automatic,  and  are  the  result  of  impulses  originating  in  the  mesence- 


282  SYSTEMATIC    FUNCTIONS 

phalon.  All  the  conductors,  without  doubt  distinct,  whose  function 
it  is  to  stimulate  in  the  cord  the  elements  which  perform  these  move- 
ments, are  contained  in  the  antero-lateral  columns  ;  the  preceding 
experiments  prove  this. 

5.  Part  played  by  the  grey  matter  in  transmission  of  motor  impulses. 
— Section  of  the  grey  matter  has  not,  as  regards  movement,  the  directly 
paralysing  effect  which  is  so  evident  in  the  case  of  sensation.  It  must 
not,  however,  be  concluded  from  this  that  it  plays  no  part  in  the  trans- 
mission of  motor  impulses.  Whether  it  is  a  question  of  motion  or  of 
sensation,  it  is  always  by  the  grey  matter  that  the  connexions  are 
effected  through  which  the  neurons  are  joined  together  in  a  successive 
order  ;  the  grey  matter  is  a  place  of  obligatory  passage  for  the  impulse 
transmitted  from  the  one  to  the  other.  The  difference,  when  the  terri- 
tories of  articulation  of  the  ascending  and  descending  neurons  in  the 
spinal  cord  are  compared,  is  that  the  first  of  these  areas  have  a  wide 
extension,  while  the  second  are  gathered  together  and  condensed  in 
the  very  place  which  corresponds  to  the  insertion  of  each  motor  root. 
From  the  experimental  point  of  view,  the  consequence  is  that  the  first 
are  encroached  upon  by  every  section  which  affects  the  grey  medullary 
matter,  while  the  second  almost  necessarily  escape  this  section  when 
it  is  made  a  little  above  the  motor  nerves  which  are  the  subject  of 
investigation.  But  if  the  destruction  of  the  grey  matter  occurs  in 
this  locality,  it  interrupts  the  communication  between  the  cortical 
spinal  elements  and  the  radicular  motor  neurons,  and  a  motor  paralysis 
is  the  result. 

Transformation  of  the  impulse. — The  grey  matter  of  the  anterior 
horns  is  not  only  a  place  of  passage,  but,  as  has  been  already  remarked 
(Vulpian),  a  place  of  transformation  of  the  impulse.  The  movements 
which  are  provoked  by  stimulation  of  the  motor  root  are  in  no  sense 
comparable  to  those  which  are  caused  by  the  stimulation  of  the  pyra- 
midal tract,  from  the  cerebral  cortex  to  the  grey  medullary  matter 
itself.  The  first  represent  a  crude  effort  of  the  muscles  working  alto- 
gether, without  direction  and  without  useful  results  ;  the  second  repre- 
sent, on  the  contrary,  an  ordered  movement,  one  whose  end  is  so  much 
the  more  clearly  defined  in  proportion  as  the  stimulation  affects  a 
more  restricted  fasciculation  in  the  thickness  of  the  pyramidal  tract. 

Transported  from  the  root  nerve  to  the  cortico-spinal  nerve,  the 
impulse  assumes  this  new  character  :  it  is  then  that  this  last  nerve  is 
able  to  distribute  it,  or  to  cause  it  to  be  distributed,  according  to  a 
definite  order,  to  a  group  of  neurons  which  make  use  of  a  muscular 
group  with  the  view  of  the  performance  of  a  definite  act.  It  is  the 
organization  of  the  motor  function  which  is  evident  in  this  example 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    283 

and  which  is  effected  by  the  connexion  of  the  neurons  in  the  grey  matter. 

().  Direct  and  crossed  action. — It  is  known  that  the  descending 
cortico-spinal  fibres  are  crossed  chiefly  in  the  bulbar  pyramids.  When 
hemisection  of  the  cord  is  effected,  which  necessarily  interrupts  these 
descending  fibres  on  the  side  to  which  they  are  distributed,  the  corre- 
sponding hmb  is  paralysed  as  regards  voluntary  movement,  as  was 
originally  pointed  out  by  Galen.  Nevertheless,  this  paralysis  is  not 
absolutely  complete,  for,  as  we  have  already  learnt  by  stimulation  of 
the  antero-lateral  columns,  a  small  portion  of  the  fibres  cross  over  in 
this  same  region  from  one  side  to  the  other.  The  preservation  of  the 
power  of  movement  on  the  side  of  the  hemisection  varies  in  degree, 
according  to  the  species,  and  also  according  to  the  conditions  of  the 
experiment. 

In  the  frog,  it  is  very  obvious  (Van  Deen,  Valentin,  Stilling)  ;  in 
mammals,  it  is  less  marked,  but  can  still  be  observed  (Stilling,  Brown- 
Sequard).  The  motor  paralysis  is  the  less  marked  in  the  corresponding 
limb  in  proportion  as  the  hemisection  is  made  more  anteriorly  as  regards 
the  motor  organs  under  consideration.  According  to  Vulpian,  a  hemi- 
section made  immediately  in  front  of  the  nerves  going  to  the  posterior 
limb  completely  paralyses  this  member  ;  if  made  in  the  cervical  region, 
the  anterior  limb  is  then  paralysed  ;  but  the  corresponding  posterior 
limb  preserves  its  movements,  as  does  that  of  the  opposite  side,  which 
is  also  slightly  weakened. 

Syncineses. — For  every  movement  in  a  determinate  direction,  such  as  flexion, 
extension,  abduction,  etc.,  of  a  limb  or  of  its  component  segments,  there  is  ob- 
viously an  association  of  muscles,  some  co-operative,  others  antagonistic,  whose 
resulting  action  determines  the  nature  of  the  movement,  together  with  its  rate, 
strength  and  all  its  special  circumstances.  This  association  can  only  take  place 
tlirougli  the  nervous  system,  and,  in  the  latter,  only  by  means  of  the  grey  matter. 
As  regards  certain  of  the  most  simple  of  these  associations,  it  is  clear  that  the 
grej'  medullary  matter  is  by  itself  alone  capable  of  performing  them.  If,  indeed, 
the  cord  be  cut  in  the  dorsal  region  of  a  frog,  and  if  some  only  slightly  sensitive 
2:)ortion  of  the  posterior  limb  be  irritated,  such  as  the  extremity  of  the  toes,  so- 
called  reflex  movements,  are  provoked,  which  are  co-ordinated  movements  ;  for 
example,  a  flexion  of  the  different  segments  of  the  limb  which  thus  avoids  the 
stimulation  ;  or,  if  the  latter  be  stronger,  it  will  be  an  abrupt  extension  of  the 
two  limbs  of  the  animal,  as  if  it  were  in  flight  (Vulpian). 

These  co-ordinated  movements,  j^erformed  by  the  cord  separated  from  the 
medulla  oblongata  (and  consecpently  separated  from  all  the  superior  centres), 
have  been  noticed  by  a  large  number  of  observers  ;  by  themselves  alone  they 
render  very  improbable  the  opinion  that  the  cord,  in  man,  is  deprived  of  all  reflex 
power.  Chau^'eau  has  remarked  them  in  the  solipedia,  Browni-Secjuard  in  the 
rabbit,  Tarchanoff  in  the  duck.  In  a  horse  or  an  ass  whose  cord  has  been  cut 
below  the  mechilla  oblongata  and  in  whom  artificial  respiration  is  performed, 
the  reflex  excitability  of  the  cord  is  very  great.  If  the  pastern  of  the  limb 
(opposite  to  that  on  which  the  animal  is  lying  in  order  that  it  may  have  liberty 
of  movement)  be  grasped,  this  limb  is  drawn  back  towards  the  trunk  by  abrupt 


284  SYSTEMATIC    FUNCTIONS 

flexion,  accompanied  with  some  alternate  movements  of  extension,  sometimes 
indeed  with  an  abrupt  extension  simulating  a  kick. 

Co-ordination  in  the  reflex  system. — A  duck,  just  decapitated  and  placed  in 
a  basin  of  water,  performs  regular  natatory  movements  which  are  provoked 
either  by  the  stimulation  of  the  superior  portion  of  the  cord,  or  by  that  of  the 
peripheral  nerves. 

In  this  case  no  other  system  of  co-ordination  can  exist  tlian  the  reflex  system, 
and  in  the  latter  there  is  no  other  locality  in  which  association  of  the  elements 
can  be  effected  save  the  grey  matter  of  the  lumbar  enlargement.  If,  instead  of 
stimulating  a  nerve  coming  from  the  skin,  we  stimulate  one  coining  from  the 
brain,  we  shall  observe  very  similar  or  very  analogous  movements,  which  are 
invariably  co-ordinated.  In  the  one  instance  as  in  the  other,  the  impulse  com- 
municated to  a  conducting  fibre  has  fallen  into  a  system  adapted  to  impress  upon 
it  its  direction,  its  succession,  its  relative  intensity ;  in  a  word,  the  order  best 
adapted  for  the  attainment  of  the  motor  results.  In  the  first  case  (reflex  action), 
it  comes  from  the  skin,  that  is  to  say,  directly  from  the  exterior  ;  in  the  second 
case  (voluntary  action),  it  comes  from  the  cerebral  cortex,  that  is  to  say,  from 
another  locality  in  which  grey  matter  exists  ;  or,  expressed  in  yet  another  way, 
from  a  systematized  whole  infinitely  more  complex  than  those  assemblages  which 
are  present  in  the  cord.  We  thus  see  this  superior  system  making  use  of  simpler 
systems  in  order  to  carry  out  actions  which  it  has  itself  prepared  by  the  work  of 
comparison,  of  co-ordination,  of  elaboration,  to  which  it  has  submitted  the 
impulse  coming  to  it  from  the  periphery,  that  is  to  say,  from  the  exterior. 

Convergence  of  the  impulses  in  the  motor  field, — In  both  cases,  an  impression 
or  an  impulse  is  carried  to  a  long  distance.  And  this  projection  is  made  in  the 
same  apparatus,  that  is  to  say,  in  the  same  small  aggregate  of  associated  nerve 
elements.  The  casual  or  original  difference  is,  however,  extreme,  since,  in  the 
first  case,  the  stimulus  is  purely  tnechanical,  while  in  the  second  it  is  physical, 
that  is  to  say,  bound  to  a  sensory  phenomenon  which  precedes  and  controls  it. 

Simple  and  complex  systems. —  By  this  analysis  the  systematization  of  the 
nervous  tissue  is  made  evident  ;  I  mean  the  association  of  its  elements  into 
systems  at  first  very  simple  which,  in  their  turn,  are  associated  in  succession  or 
in  juxtaposition,  so  that  they  form  larger  systems  ;  and  it  is  the  same  with  these 
latter,  so  that  the  nervous  system  properly  so  called  may  be  built  up.  Of  what- 
ever nature  the  system  to  which  we  turn  our  attention  may  be,  whether  simple 
or  complicated,  we  shall  find  in  it  internal  bonds  of  union  which  assure  its  con- 
tinuance and  also  its  functional  individuality,  and  external  bonds  of  union,  wMch 
connect  it  to  others  in  a  larger  system  and  one  of  different  order. 

Indeterminate  limits  ;  Changing  constitution. — The  greatest  difficulty  con- 
sists in  tracing  the  exact  limits  of  these  associations  and  the  exact  order  in  which 
they  are  superposed  and  fitted  together,  because  obviously  these  boimdaries 
are  not  definitely  determined  or  fixed  in  their  sitviation.  When  the  imjDidse 
arrives  in  a  system  and  spreads  through  it,  it  seems  to  fade  away  at  its  bound- 
aries by  insensible  diminution  ;  it  is  resolved  in  order  that  with  certain  of  its 
elements  it  may  reproduce  another  impulse  with  the  object  of  performing  a 
different  action.  This  is  at  least  the  case  as  regards  especially  the  actions  known 
as  those  of  the  life  of  relation  with  the  exterior  ;  the  internal  functions  of  the 
vegetative  life  are  much  more  fixed  and  uniform,  and  their  changes  are,  indeed, 
restricted  to  an  obvious  periodicity. 

Method  of  association  of  the  neurons. — Concerning  the  mode  of  association 
of  nerve  elements,  in  order  that  definite  functional  groups  may  be  formed,  ana- 
tomy has  supplied  some  important  information.  These  elements  enter  into 
relation  and  communicate  the  impulse  which  has  put  them  in  action  by  their 
ramified  prolongations.     The  knowledge  of  these  relationships,   not  merely  in 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    285 

general,  but  also  in  detail,  would  be  of  the  highest  interest,  because  it  is  clear 
that  on  the  special  disposition  of  these  connexions  the  functional  associations 
whicli  we  endeavovu'  to  'ascertain  depend.  The  little  that  is  known  on  this  point 
deserves  to  be  recorded. 

Overlapping  of  the  Polar  Fields. — When  two  neurons  transmit  the  impulse,  the 
polar  fields  (terminal  of  the  one  and  initial  of  the  other),  greatly  ramified,  by 
which  they  come  into  relationship,  are  not  exclusively  but  only  partially  super- 
posed, while  the  remainder  corresponds  to  portions  of  polar  fields  belonging  to 
other  neurons. 

In  this  manner  a  neuron  transmits,  or  can  transmit,  the  impulse  to  several  others 
(sometimes  to  a  very  large  number),  and  distributes  it  thvis  in  very  diverse  and 
remote  regions  ;  conversely,  a  neuron  receives  the  impulse  from  several  others 
(sometimes  also  from  a  very  large  number)  and  concentrates  it  in  one  point  after 
having  received  it  from  multiple  and  distinct  regions. 

Examples. —  The  spinal  cord  supplies  us  with  very  characteristic  examples  of 
both  arrangements.  An  element  of  a  posterior  root,  taken  by  itself,  distributes 
the  impulse  (by  means  of  the  grey  matter)  to  radicular  motor  neurons,  to  the 
cerebellum,  to  the  cerebellar  cortex,  to  the  optic  thalamus,  speaking  only  of  the 
principal  localities  towards  which  it  is  distributed.  An  element  of  an  anterior 
root,  taken  by  itself,  receives  the  impulse  (by  means  of  the  grey  matter)  from 
posterior  radicular  neurons,  from  the  cerebelkmi,  the  optic  thalamus,  the  cerebral 
cortex,  etc.  (see  Fig.   104). 

Direct  and  derived  transmission. —  Another  method  of  formulating  the  relation- 
ships in  a  more  general  and  synthetic  fashion  is  the  following  : — 

When  two  neurons  transmit  the  impulse  to  each  other  they  generally  do  so  in  two 
ways,  namely  :  (1)  directly  by  their  own  prolongations  :  (2)  indirectly  by  neurons 
placed  derivatively  on  these  terminations.  These  derived  neurons,  when  they  are 
short,  are  called  associating  nem-ons.  As  a  matter  of  fact  they  are  of  all  possible 
lengths.  When  we  especially  exaixdne  the  connexion  of  the  posterior  and  an- 
terior radicular  nevirons  of  the  cord  we  see  them  communicating  the  impulse,  in 
addition  to  their  direct  prolongations,  by  means  of  the  cerebellum,  of  the  cortex, 
of  the  cerebral  ganglia.  Other  paths  of  association,  medium,  short,  very  sliort, 
fill  up  the  gaps  left  between  these  remote  masses. 

Elements  of  projection  and  elements  of  association. —  To  speak  precisely,  the 
so-called  elements  of  projection  are  elements  of  association  when  they  unite  the 
nervous  organs  ;  two  masses  of  grey  matter,  however  remote  the  latter  inay 
be  ;    for  these  elements  have  all  possible  dimensions. 

Each  segment  of  tlie  spinal  cord,  even  when  regarded  as  separated  from  its 
neighbours  by  section,  still  contains,  for  its  own  special  functional  activity,  these 
short  cells  of  association,  which  doulatless  take  part  in  the  most  simple  reflex 
actions  arising  in  these  segments.  Further,  the  neighbouring  or  more  or  less 
remote  segments  are  connected  by  elements  of  the  same  kind,  whose  length  is 
progressively  greater.  These  cells,  known  as  co-ordinating  or  commissural, 
often  present  an  arrangement  which  explains  the  redistribution  which  they 
impose  on  the  impulse  reaching  them.  Their  dendrites  are  limited  to  the  cir- 
cumference of  the  cell  ;  in  other  words,  their  recepti\'e  pole  covers  a  limited 
field.  Their  axon,  after  running  a  short  course,  divides  into  two  branches,  the 
one  usually  ascending,  the  other  descending  in  the  columns,  and  sends  collaterals 
to  the  grey  matter  to  which  they  return  ;  their  chstributive  pole  occupies  a 
relatively  very  extended  area. 

The  large  commissures  which  connect  the  cord  to  the  superior  grey  masses, 
when  they  arrive  at  the  latter,  obey  in  their  turn  the  same  law.  The  ascending 
and  descending  elements  which  compose  them  form  direct  connexions  in  these 
masses  by  articulation  of  the  one  with  the  other  ;   but,  further,  they  are  second- 


286  SYSTEMATIC    FUNCTIONS 

arily  connected  by  elements  of  association  or  of  derivation  of  diverse  and 
extremely  numerous  categories,  whence  arises  the  very  complicated  structure 
of  these  organs. 

Extra  and  intra-medullary  distribution  of  the  impulses  by  the  same  neuron.^ — 
It  is  owing  to  the  advance  in  anatomical  methods  that  it  is  now  possible  to  say,. 
from  the  inspection  of  a  neuron,  which  are  the  points  in  it  of  entry  and  of  exit 
of  the  impulse.  The  radicular  motor  neurons  of  the  spinal  cord  receive  the 
impulse  by  their  dendrites  (formerly  known  as  protoplasmic  prolongations)  ; 
they  transmit  it  by  their  axis  cylinder  or  axon,  which  carries  it  to  the  inuscles 
by  these  ramified  terminations  ;  but,  before  leaving  the  cord,  this  axis  cylinder 
gives  off,  in  its  course  through  the  anterior  coruna,  collateral  branches,  which, 
iDcfore  leaving  this  organ,  distribute  in  it  a  portion  of  the  impulse  to  the  elements 
which  approximate  them.  It  hence  follows  that  the  radicular  muscles  excite 
not  only  the  muscles,  but  the  motor  neurons  in  their  vicinity,  which,  in  their 
turn,  finally  discharge  the  impulse  received  in  the  inuscles  ;  in  other  words,  and 
conformably  to  the  general  law,  they  stimulate  the  muscles  at  the  same  tiine 
both  directly  and  indirectly,  and  furnish  a  new  example  of  this  overlaj^ping  of 
the  nerve  elements  the  one  over  the  other,  which  aj^pears  to  be  the  fundamental 
rule  presiding  over  their  connexions. 

Another  example. — The  neurons  of  the  pyramidal  tract  offer  an  arrangement 
of  the  same  kind  which  is  still  more  definite.  Their  axis  cylinder,  near  its  origin, 
supplies  collaterals  of  which  certain  very  long  ones  woiild  represent,  at  all  events 
jsartially,  the  fibres  of  the  corpus  callostmi,  which  functionally  connect  one  hemi- 
sphere with  the  other  ;  further,  in  the  locality  in  which  it  passes  through  the 
pons,  it  supplies  others  not  less  remarkable  on  account  of  their  situation,  in  the 
middle  course  of  the  axon  which  furnishes  them,  and  wliich  distribute  the  im- 
pulse to  elements  which  proceed  to  the  cerebellum  by  its  middle  peduncle. 

Thus  an  impulse,  even  if  supposed  to  be  localized  in  the  dendritic  plume  of  a 
neixron  of  the  pyramidal  tract,  has  several  paths  open  to  it  by  which  it  can  attain 
the  motor  nuclei  of  the  spinal  cord  ;  the  one  direct,  long  known  ;  the  others 
indirect,  by  the  opposite  hemisphere,  and  by  the  cerebellum,  without  including 
other  possible  paths,  all  of  which  converge  towards  the  anterior  horns.  And 
having  arrived  there,  the  same  scheme  is  reproduced,  but  in  a  more  restricted 
manner  as  regards  the  radicular  netu-ons,  which  carry  this  impulse  to  the  muscles 
dii-ectly  by  their  terminations  and  indirectly  by  their  collaterals.  The  nervous 
organization  thus  seems  to  have  for  its  first  and  essential  aim  the  multiplication 
as  regards  the  impulse  of  the  paths  and  conflicts,  to  drive  it  back  from  element 
to  element,  and  to  graduate  its  rate  before  recondensing  it  on  the  extreme  term- 
inations of  the  motor  paths  in  order  to  impose  on  it  an  order,  a  definite  succession 
adapted  to  the  result  to  be  obtained. 

B.  ANIMAL    AND    ORGANIC    LIFE— THE    GREAT    SYMPATHETIC. 

Anatomists,  and  witli  them  many  physiologists,  divide  the  nervous 
system  into  two  great  secondary  systems  :  the  one  known  as  the 
cerebro-sjnnal  system,  the  other  as  the  great  sympathetic  system,  both 
recognizable  by  very  obvious  external  characters.  According  to  them, 
and  following  the  ideas  and  expressions  of  Bichat,  the  first  takes  part 
in  functions  of  the  so-called  animal  life,  or  that  of  relation,  the  second 
in  the  functions  of  the  vegetative  life  or  that  of  nutrition.  At  the  first 
glance  these  expressions,  and  the  ideas  which  they  formulate,  appear 
to  be  very  clear ;  experiment  has  not  formally  contradicted  them ;  in 


CONSCIOUS  AND  UNCONSCIOUS  :   THEIR  SEPARATION    287 


enforcing  precision,  it  has  gradually 
shown  that  they  are  too  schematic 
and  too  absolute.  Each  of  these 
terms,  both  from  the  anatomical  and 
physiological  point  of  view,  ought  to 
be  defined  ;  and  it  is  by  bringing 
these  definitions  in  accord  with  the 
experimental  data  that  the  degree 
to  which  they  have  changed  since 
the  time  of  Bichat  is  recognized. 

1.    The  two  lives  :  their  distinct  repre- 
sentation in  the  nervous    system 

Are  there  then  in  reality  two  lives, 
the  one  animal  the  other  vegetative? 
Is  the  animal  life  represented  by  a 
collection  of  organs  possessing  sen- 
sation, intelligence,  motor  power, 
grafted  on  a  vegetable  life  repre- 
sented by  organs  of  nutrition,  to  such 
a  degree  that  it  is  possible  to  ascer- 
tain and  follow  out,  scalpel  in  hand, 
the  manner  in  which  one  is  fused  to 
the  other  ?  No  ;  Bichat's  definition 
has  only  a  figurative,  an  imaginary 
value.  It  is  certainly  very  deep,  but, 
from  that  very  fact,  it  eludes  a  simple 
localization  such  as  that  pointed  out 
above,  which  nevertheless  has  the 
great  merit  of  being  easily  grasped 
on  account  of  its  simplicity.  Aristotle 
had  already  observed  that  the  func- 
tions of  the  living  being  may  be 
divided  into  two  orders  :  the  one 
regarding  more  especially  its  con- 
servation (vegetative  functions  or 
those  of  nutrition),  the  other  concern- 
ing its  connexions  with  the  living 
world  external  to  itself  (social  func- 
tions or  those  of  relation).      By  re- 


r^^ 


Xeck 


I'pper  limb 


Chest 


Xi 


Lower  limb 


'< 


Fig.   118. — Deep  nervovis  system. 
The  encephalon,  the  spinal  cord,  the  great  sympathetic. 


288  SYSTEMATIC    FUNCTIONS 

garding  the  internal  organs  such  as  the  heart,  the  lung,  the  intestine,  it 
becomes  obvious  that  they  are  intended  for  maintenance  of  life,  for 
nutrition  ;  on  the  other  hand,  the  organs  of  sense,  the  apparatus  of 
expression  and  of  external  movement,  are  adapted  for  the  relationship 
of  the  animal  with  the  medium  which  surrounds  it,  and  especially 
with  the  living  world.  But  the  line  of  division  is  not  fixed  at  the  im- 
mediately visible  organs.  Every  cell,  every  organized  part,  presents 
it  once  again  in  its  more  restricted  area  ;  in  every  cell  indeed  there  is 
a  portion  of  the  protoplasm  which  is  especially  concerned  with  its 
maintenance  and  conservation,  and  another  portion  which  discharges 
the  social  function  with  regard  to  other  cells,  bringing  them  into  rela- 
tion with  itself. 

And  if  ever  analysis  shall  penetrate  still  farther  into  the  organization 
of  this  complex  being,  the  cell,  the  same  division  will  apply  to  every 
differentiated  portion  of  this  miniature  organism.  In  short,  animal 
life  and  vegetative  life  are  not  two  separate  things,  but  two  different 
aspects  of  the  functions  of  the  living  organization,  aspects  which  are 
encountered  in  every  system  of  complicated  organs  when  they  are 
analysed.  Each  group  is  united  to  analogous  groups  by  external  bonds 
of  union,  while  its  constituent  parts  are  connected  amongst  themselves  by 
bonds  of  union  internal  to  the  group  itself.  The  totality  of  the  living 
kingdom  is  a  system  of  this  kind  which  analysis  decomposes  into  smaller 
and  smaller  groups,  until  the  elements  of  dead  or  of  mineral  nature  are 
reached. 

So-called  Cerebro-spinal  and  Great  Sympathetic  Systems. — To  return 
to  the  systems  known  as  cerebro-spinal  and  great  sympathetic  ;  their 
reciprocal  functions  are,  as  a  whole,  those  of  relation  (like  every  nervous 
function)  ;  only  the  first  established  relations  between  the  organism  and 
the  exterior,  while  the  second  forms  relationships  between  the  organs  of 
the  same  org'am^m,  indirectly  for  certain  of  these  organisms,  directly  as 
regards  those  which  exercise  the  conservative  function  known  as  that 
of  nutrition.  This  much  being  said  concerning  their  functions,  how 
should  these  two  systems  be  limited  the  one  with  regard  to  the  other  ? 
Signification  attributed  to  these  terms. — On  this  point,  as  also  con- 
cerning the  former,  the  ordinary  meaning  attributed  to  the  terms 
cerebro-spinal  and  great  sympathetic  is  illusory,  because  it  is  too  absolute. 
Clearly  distinct  at  the  periphery,  at  the  level  of  the  differentiated 
organs  between  which  they  are  distributed,  these  two  systems  form  a 
single  one  in  the  superior  portions  of  the  nervous  system,  in  order  to 
ensure  the  unity  of  the  latter  and  hence  that  of  the  organism.  Al- 
though the  anatomist,  for  reasons  of  convenience,  traces  a  conven- 
tional line  of  demarcation  between  the  two,  this  is  merelv  a  device, 


CONSCIOUS  AND  UNCONSCIOUS  :     THEIR  SEPARATION  289 


certainly  a  useful  one,  but  which  must  not  cause  us  to  lose  sight  of 
the  reality. 

The  brain  and  the  spinal  cord  enclosed  in  an  osteo-fibrous  cavity 
(the  encephalo-spinal  cavity)  form  an  apparently  homogeneous  mass, 
which  is  invariably  compact  and  known  as  central.  Nerves  arise  from 
the  spinal  cord  and  by  their  prolonga- 
tions form  a  feltwork  of  conducting 
fibres  which  are  known  as  the  'peri- 
pheral  nerves.  This  central  mass, 
with  its  feltwork,  is  the  cerebro- 
spinal system  of  anatomists. 

On  the  other  hand,  nerve  roots  are 
seen,  after  leaving  the  spinal  cord, 
to  be  detached  from  small  bundles 
(communicating  branches),  projecting 
themselves  into  a  double  chain  inter- 
rupted by  ganglia,  and  from  Avhich 
cords  arise  forming  a  plexiform  whole, 
itself  being  strewn  with  ganglia,  which 
proceed  to  the  pulmonary,  digestive 
and  vascular  apparatus,  that  is  to  say, 
to  the  organs  of  nutrition  :  this  is  the 
great  sympathetic  system  such  as  it 
is  still  described  in  all  treatises. 

Intra-rachidian  prolongation  of  the 
Great  Sympathetic  System. — Experi- 
ment has  convincingly  shown  that 
this  second  system  communicates 
with  the  cord,  and  therefore  with  the 
brain  itself,  with  which  it  effects  an 
exchange    of    impulses.       Thus    the 

^  \  Sciaiie 

division  of  nerves  into  those  of  nutri- 

.  Fig.    119. — Encephalon,    spinal    cord, 

tion  and   those    of    exterior   relation  is       and  great  sympathetic  in  the  frog. 

inaccurate,  and  the    terms  which  de-     3,  ocuio-motor ;    4,  pathetic ;    5,  tri- 

„  .,  T  ,.  .^       .  geminal  ;   8,  aiiditory  ;    10,  pneumogastric. 

nne  it  are  aecej)tive  ;  it  gives  a  pre- 
ference to  the  second  to  the  detriment  of  the  first.  The  cerebral  and 
spinal  mass  is  not,  as  is  obvious,  excluded  from  the  control  of  nutrition, 
the  great  sympathetic  is  not  the  only  one  to  safeguard  the  conservation 
of  the  organism.  This  has  long  been  recognized,  and  has  been  for  certain 
observers  a  reason  why  they  deny  all  distinction  between  animal  and 
nutritive  functions  and  reject  every  systematization  based  on  this 
distinction.  This  is  to  fall  into  the  opposite  mistake  ;  it  is  to  introduce 
P.  u 


Crural 


290 


SYSTEMATIC    FUNCTIONS 


confusion  once  more  into  a  subject  which  can  be  rendered  clear  only 
by  persevering  analytical  efforts. 

Of  the  theory  of  Bichat  the  most  essential  part  must  be  retained,  but  its  formula 
must  be  corrected  in  such  a  way  as  to  make  it  agree  with  the  facts  of  experiment. 
It  is  especially  necessary  to  discard  designations  which  are  deceptive,  or  which 
have  only  an  indefinite  meaning.  The  system  which  physiology  describes  as 
that  of  "  animal  life  "  is  not  exactly  that  which  anatomy  calls  "  cerebro-spinal  "  ; 
its  limits  are  less  wide  than  this  designation  indicates,  since  the  cord  and  the 
brain  are  also  concerned  in  vegetative  life  and  contribute  to  regulate  it  as  well 
as  that  known  as  animal  life.  Conversely,  the  system  which  physiology  calls 
"  vegetative  life  "  is  not  merely  that  which  anatomy  describes  as  "  sympathetic," 
a  term  which,  further,  has  no  longer  any  meaning,  the  sympathies  (a  kind  of 
functional  consensus  which  the  old  physiology  held  to  exist  between  i-emote 
organs)  being  assured  as  much  by  one  of  the  two  systems  as  by  the  other,  and 
reciprocally. 

In  spite  of  tliis,  the  anatomical  expressions  currently  used  will  still  be  em- 
ployed, even  by  those  who  appreciate  their  inaccuracy  or  their  insufficiency. 
We  must  therefore  make  use  of  them ;  and  this  is  the  reason  why  it  is  necessary 
accurately  to  define  the  true  meaning  which  attaches  to  them. 

Motor  Neroes  Anatomical  differ- 

^  ^  -  ence  between  the  two 

systems. — From  the 
point  of  view  of  de- 
scriptive anatomy, 
the  difference  which 
exists  between  the 
animal  and  the  vege- 
tative life  is  that  the 
first  has  its  grey 
matter,  its  centres, 
altogether  contained 
in  the  cerebro-spinal 
cavity,  while  the 
second  has  a  portion 
of  this  grey  matter 
distributed      outside 


Intraspinal 


hxtr-i-symM 


^ 


a 
a 


o 


i] 


o 

o 


II> 


Fig.  riO. — Diagram  showing  tlie  anatomical  characteris- 
tics of  the  motor  systems,  one  being  volvmtary  and  the 
other  involuntary. 

As  regards  the  first  (called  cerebro-spinal)  the  locality  of  union 
of  the  two  orders  of  peripheral  and  deep  neurons  is  intra- 
spinal :  as  concerns  the  second  (known  as  great  sympathetic), 
it  is  extra -spinal. 

Motor-nerves  in  black,  excito-motor  in  blue,  inhibitory  in  red. 


this  cavity.  This  extra-sj)inal  grey  matter,  represented  by  the  ganglia 
both  of  the  chain  and  the  plexiform  cords  of  the  second  system,  is  pre- 
cisely that  which  distinguishes  the  great  sympathetic  from  all  other 
nerves.  The  great  sympathetic  is  a  sort  of  spinal  cord,  or  a  portion  of 
the  spinal  cord,  disserninated  in  the  nutritive  apparatus.  The  chief 
nervous  mechanisms,  such  as  the  reflexes,  inhibition,  summation  of 
stimuli,  etc.,  are  recognized  by  experimental  analysis,  both  in  the  meta- 
meric  segments  of  the  spinal  cord  and  in  the  ganglia  of  the  great  sympa- 
thetic.    The  grey  matter  of  the  ganglia  is  further  constructed  histo-. 


CONSCIOUS  AND  UNCONSCIOUS  ;    THEIR  SEPARATION    291 


logically,  as  regards  its  main  out- 
lines, in  the  same  manner  as  the 
spinal  cord  and  the  brain  ;  arbori- 
zations of  neurons,  some  terminal, 
others  initial,  are  intermixed  and 
articulated  in  it  as  in  the  grey 
medullary  axis  and  the  cerebral 
cortex  ;  and,  further,  the  swollen 
bodies  of  these  neurons  find  place 
in  it  in  the  midst  of  these  arbori- 
zations. 

The  limits  of  the  Great  Sympathetic. 
— In  accepting  the  great  sympathetic 
as  the  extra-spinal  portion  of  the  ner- 
vous system  of  vegetative  life,  it  is  still 
necessary  to  define  the  limits  which 
appertain  to  it,  and  on  tliis  point  the 
confusion  has  been  great.  As  has  been 
mentioned,  the  great  sympathetic  is 
continuous  with,  and  has  the  same 
origin  as,  the  cord.  But  the  latter  com- 
prises two  portions,  namely,  the  spinal 
cord  and  the  medulla  oblongata.  The 
relations  of  the  great  sympathetic  with 
the  spinal  cord  should  be  taken  as  a 
type  for  the  description  because  they 
arc  simple  and  symmetrically  repeated 
throughout  the  length  of  the  medullary 
cylinder.  The  relations  of  the  sym- 
pathetic witli  the  medulla  oblongata, 
in  which  the  typical  form  of  the  coi'd, 
properly  so  called,  has  disap2:)eared, 
will  only  become  clear  by  comparing 
them  with  the  arrangement  of  this 
latter. 

Its  communicating  branches.  — 
From  each  mixed  trvmk  resulting  from 
the  fusion  of  the  anterior  and  posterior 
roots  of  a  spinal  nerve  a  small  branch 
called  communicatimj  is  detached,  which 
proceeds  to  enter  the  chain  of  each  of 
the  great  symj^athetic  at  the  level  of 
each  of  its  ganglia.  Having  arrived  in  the 
chain,  the  fibres  of  this  branch  ascend 
or  descend  through  the  length  of  the 
latter,  following  a  variable  coiirse,  be- 
fore again  leaving  it,  also  at  the  level  of 
one  of  its  ganglia.  The  origins  of  the 
great  sympathetic  are  situated  both  in 
the    cord    and    the    ganglia,    including 


Fig.  121. — Diagram  of  the  great  sym- 
pathetic representing  its  visceral  dis- 
tribution. 

On  the  right,  medulla  oblongata,  spinal 
cord  and  roots.  In  the  middle,  vertebral 
chain  and  its  ganglia.  On  the  left,  second 
chain  (prevertebral),  formed  by  the  pneumo- 
gastric  nerve  and  the  mesenteric  nerves,  solar 
plexus,  and  hypogastric  plexus.  On  the  ex- 
treme left,  terminal  ganglia  and  plexuses  of 
the  viscera. 

The  break  between  peripheral  and  deep 
neurons  is  effected  either  in  the  catenary, 
terminal  or  intermediate  gangUa. 

Symmetrical  with  regard  to  a  plane  xy 
which  intersects  the  thorax.  Principal  con- 
densed origins  in  the  thoracic  region.  Sup- 
plementary origins  arising  from  the  medulla 
oblongata  (nerve  of  Wrisberg  and  pneumo- 
gastric)  and  from  the  sacral  spinal  cord 
(erector  nerves). 


292  SYSTEMATIC    FUNCTIONS 

those  of  the  chain  ;  by  this  is  implied  that  the  fibres  coming  from  the  spinal 
cord  are,  at  least  partially,  interrupted  in  the  chain.  Thus  from  the  chain 
branches  are  given  off  which,  after  having  formed  plexuses  and  passed  through 
new  ganglia,  are  distributed  in  the  tliree  great  nutritive  apparatus,  the  digestive 
tube,  the  'pulmonary  apparatus,- the  vascular  apparatus,  and  also  in  the  genital 
apparatus  in  its  deep  organs. 

Its  visceral  and  cutaneous  branches. — As  regards  the  organs  which  form 
clearly  individvialized  masses,  such  as  the  intestine  and  its  large  glands,  or  the 
heart  and  the  aorta,  these  branches  extend  directly  from  the  chain  to  these 
organs  ;  but  as  concerns  those  which,  like  the  muscular  and  cutaneous  vessels  or 
the  cutaneous  glands,  are  disseminated  interstitially  in  organs  other  than  those  of 
nutrition  (in  order  to  ensure  their  nutrition),  they  follow  the  common  path  of 
he  nerves  of  these  organs.  For  this  purpose  they  extend  from  the  chain  to  the 
mixed  rachidian  trunk,  by  following  the  coimmmicating  branch  in  the  opposite 
direction  to  that  of  the  fibres  coming  from  the  spinal  cord,  and,  having  arrived 
at  this  trunk,  they  follow  it  towards  the  periphery  to  filially  reach  the  contractile 
or  secretory  elements  for  which  they  are  intended.  A  nerve  like  the  radial,  the 
sciatic,  or  the  trigeminal,  is  thus  mixed,  not  only  because  it  contains  sensory  and 
motor  elements  of  the  conscious  or  voluntary  order,  but  also  because  it  contains 
others  belonging  to  this  unconscious  or  sub-conscious  system  which  the  great 
sympathetic  helps  to  characterize. 

Its  sensory  elements. — In  the  preceding  description  we  have  endeavoured  to 
trace  an  involuntary  motor  fibre  from  the  cord  to  its  termination,  in  the  direction 
of  its  conduction.  The  great  sympathetic  contains,  together  with  these  motor 
fibres,  sensory  elements  which  duplicate  them  and  whose  conductivity  is  naturally 
opposed  ;  but  having  made  this  reservation,  their  arrangement  should  be  the 
same.  As  a  matter  of  fact,  the  constitution  of  the  great  sympathetic  has  been 
ascertained  by  experiments  made  on  its  motor  portion  ;  the  sensibility  of  the 
oro-ans  of  nutrition  is  too  obtuse  to  be  appealed  to  as  a  witness  as  experimental 
evidence  ;  the  sensibility  known  as  reflex  might  serve  for  such  a  research  which 
is  still  very  little  advanced. 

Metameric  arrangements  :  Ganglia.— The  chain  of  the  great  sympathetic 
forms  its  axis  or  chief  part.  Its  resemblance  to  the  spinal  cord  is  striking  ;  as  a 
rule  there  are  on  each  side  as  many  ganglia  as  vertebra?,  as  many  communicating 
branches  as  nerve  pairs.  Yet,  in  the  cervical  region  several  of  these  ganglia 
coalesce,  the  number  being  reduced  to  three  for  seven  vertebra?.  Of  these  three 
ganglia  there  is  one  (the  first  thoracic,  still  known  as  the  stellate  ganglion)  which 
represents  a  fusion  of  ganglia,  some  of  which  belong  to  the  inferior  portion  of 
the  cervical  region,  otliers  to  the  superior  portion  of  the  thoracic  region.  Above 
the  superior  cervical  ganglion,  the  great  sympathetic  chain  seems  to  disappear 
and  to  be  entirely  absent  in  the  prolongation  of  the  spinal  cord  known  as  the 
bulb  or  the  medulla  oblongata.  In  reality  a  trace  of  it  has  been  recognized  in 
the  anastomosis  which  proceeds  from  the  superior  cervical  ganglion  to  the 
Gasserien  ganglion  :  this  is  at  least  the  conclusion  at  which  I  have  arrived  as 
the  result  of  my  dissections  and  my  experiments  on  animals,  in  which  this  anas- 
tomosis has  more  importance  on  account  of  the  predominance  of  the  face  over 
the  brain.  From  the  Gasserien  ganglion,  the  fibres  of  this  anastomotic  branch 
follow  the  branches  of  the  trigeminal,  which  they  once  more  leave  in  order  to 
reach  the  ganglia  annexed  to  these  branches  (ophthalmic,  spheno-palatine  and 
otic  ganglia). 

Cranial  Sympathetic. — In  this  region  the  sympathetic  chain  has  the  same 
relationships  with  the  medulla  oblongata  as  lower  down  with  the  vertebral 
spinal  cord.  By  the  roots  of  the  trigeminal  it  receives  new  origins  from  the 
bulb,  while  it  supplies  branches  of  distribution  to  the  branches  of  the  trigeminal, 


CONSCIOUS  AND  UNCONSCIOUS  .  THEIR  SEPARATION     293 


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coming  from  below  (from  the  spinal  cord),  and  which  proceed  together  to  the 
organs  placed  in  the  field  sujiplied  by  tliis  nerve.  Above  this  point,  still  other 
nerves,  the  motor 
nerves  of  the  eye, 
supply  to  it  small 
branches  of  simi- 
lar origin,  such  as 
the  large  and 
short  branch  of 
the  oculo-motor 
nerve.  Below, 
that  is  to  say,  be- 
tween the  t  r  i- 
geminal  and  the 
first  cervical  pair, 
the  connexions  of 
the  chain  with  the 
bulbar  nerves, 
sucli  as  the  facial, 
the  glosso-phary  n- 
geal,  the  pneu- 
niogas  trie  and 
spinal  accessory, 
are  but  little  ob- 
vioiis,  or  are  re- 
duced to  insignifi- 
cance. This  is 
not  the  same  thing 
as  to  say  that 
these  nerves  are 
not  related  to  the 
great  s  y  m  p  a  - 
thetic  ;  only  these 
relations  are 
effected  in  a  less 
simple  manner, 
less  systematical- 
ly than  witli  the 
trigeminal,  in 
which  the  asjject 
of  a  spinal  jjair  is 
still  recognizable, 
and  especially  as 
regards  the  spinal 
roots. 

The  facial,  by 
its  small  root 
( nerve  of  Wris- 
berg),  svipplies 
fibres  which,    like 

the  two  petrosal  and  the  chorda  tympani  branches,  proceed  to  the  spheno-palatine, 
otic  and  sub-maxillary  ganglia  and  manifestly  come  from  the  origins  of  the  great 
sympathetic.  The  glossopliaryngeal,  by  its  branch  of  Jacobson,  gives  off  similar 
filaments.     As  to   the  pneiunogastric   and  spinal  accessory,  these  large  nerves. 


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3   5   3-53 


294  SYSTEMATIC    FUNCTIONS 

form  only  moderately  fine  anastomoses  with  the  chain  at  the  superior  cervical 
ganglion,  but,  fui'ther  on,  a  large  j^ortion  of  their  fibres  pass  into  the  pharyngeal, 
•oesophageal,  gastric,  pulmonary  cardiac  plexuses,  while  their  terminations  form, 
in  the  abdomen,  one  of  the  most  important  origins  of  the  solar  plexus.  The 
hj'^poglossal  much  resembles  in  its  constitution  the  arrangement  of  a  spinal  pair 
as  regards  its  connexions  with  the  great  sympathetic. 

Its  bulbar  origins. — In  these  bulbar  nerves,  which  seem  to  elude  the  typical 
arrangement  of  the  spinal  roots,  and  to  which  for  this  reason  special  names  have 
been  given,  instead  of  simple  nvuiierals,  this  arrangement  when  sought  for  is 
practically  found  to  be  present ;  it  is  obvious,  whether  it  is  a  question  of  the  rela- 
tionships, of  sensation  to  movement,  or  whether  of  those  which  connect  the  vohm- 
tary  to  the  involuntary  nerves  for  the  performance  of  functions  as  a  whole.  The 
difference  lies  especially  in  the  fact  that,  in  the  regions  of  the  organism  (thorax, 
abdomen)  in  which  the  metameric  division  of  the  vertebrae*  is  recognizable  at 
first  glance,  similitude  of  form  justifies  the  inference  of  similitude  of  function 
directly  experiment  has  determined  this  as  concerns  any  one  of  tliese  metameric 
groups.  In  localities  where  this  arrangement  has  been  upset  by  new  superadded 
formations  (skull),  such  an  inference  is  impossible,  and  as  regards  each  nerve, 
each  nerve  branch,  this  function  must  be  determined  by  exj^eriment.  It  is  for 
this  reason  that  there  is  a  series  of  nerves  called  cranial,  which  are  not  included 
in  the  general  formulae  comprising  the  grouping  of  nerves  of  different  functions, 
formulae  based  on  experiments  carried  out  on  the  spinal  nerves.  The  nature 
of  this  grouping  is  in  no  sense  absolute  ;  tlie  separation  into  metameres  does 
not  express  an  absolute  physiological  necessity,  but  a  fact  of  development,  of 
evolution,  the  reason  of  which  lies  in  the  past.  Wliether  these  conducting  fibres 
are  gathered  together  into  bundles  more  or  less  numerous,  more  or  less  volumi- 
nous, or  more  or  less  resembling  one  another,  is  of  little  importance  as  concerns 
the  function  ;  the  essential  point  is  that  they  have,  individually,  relationships 
which  are  appropriate  to  their  origin  and  to  their  termination  ;  the  rest  is  con- 
tingent. 

Myelinated  and  non-myelinated  fibres. — The  fibres  of  the  great  sympathetic 
are  'myelinated  fibres,  usually  of  small  diameter.  Near  to  their  cell  of  origin  and 
near  to  their  termination  they  lose  their  myelin  sheath,  which  has  led  to  the 
formation  of  a  category  of  fibres  known  as  those  of  Eemak  or  non-myelinated 
fibres,  which  were  formerly  considered  as  being  special  to  the  great  sympathetic  ; 
they  are  but  prolongations  of  the  first.  This  arrangement  is  not,  as  has  been 
thought,  peculiar  to  the  great  sympathetic,  but  is  merely  much  exaggerated  in 
it.  When  these  non-myelinated  fibres  predominate  over  the  others  (as  in  the 
neighbourhood  of  the  ganglia),  the  nerves  assvune  a  greyish  colour  which  en- 
croaches on  the  ordinary  wliitish  colour  of  nerves. 

White  and  grey  branches. — Onodi  and  Gaskell  have  noticed  that  the  com- 
municating branches  which  unite  the  mixed  spinal  trunk  to  the  sympathetic 
chain,  are,  some  of  them,  whitish  and  others  grey.  The  first  would  especially 
contain  the  fibres  of  origin,  the  second  those  of  distribution.  The  communicating 
branches  of  the  thoracic  region  are  white  ;  they  represent  especially  fibres  of  origin 
which  effect  a  connexion  between  the  cord  and  the  chain  ;  those  of  other  local- 
ities, in  jDroportion  as  we  get  farther  away  from  the  thorax,  are  grey :  they  especially 
represent  fibres  of  distribution  proceeding  from  the  chain  to  the  organs.  These 
facts  are  in  accord  with  the  remark  which  I  have  previovisly  made,  based  upon 
experimental  data,  that  the  origins  of  the  great  sympathetic  are  especially  condensed 
in  the  thoracic  region  of  the  spinal  cord. 

Ganglia  ;  grey  matter. — The  ganglia  of  the  great  sympathetic,  studied  by 
the  new  methods,  present  the  general  structure  and  character  of  grey  matter. 
It  has  long  been  knowoi  that  they  contain  nerve  cells  (the  body  of  the  cells  of 


CONSCIOUS    AND  UNCONSCIOUS  :    THEIR  SEPARATION    295 


the  nevirons).  It  has  since  been  ascertamed  that  tliey  also  contain  ramified 
lorolongations  which  radiate  around  these  cells  and  cause  them  to  resemble  those 
of  the  cord  and  of  the  brain.  It  is  also  adinitted  that  these  jarolongations  have 
free  terminations,  which  come  in  contact  with  the  axis-cylinder  ramifications  of 
the  neurons  which  carry  the  impulse  to  them. 

These  are  all  characters  which  draw  together  the  ganglia  of  those  nervous 
organs  which  are  known  as  centres,  and  they  are  in  unison  on  the  other  hand 
with  the  data  concerning  them  furnished  by  experiment. 

In  a  sense,  they  are  localities  in  which  nerve  conductors  are  interrupted  or, 
which  amounts  to  the  same  thing,  sites  of  association  for  neurons  which  enter 
into  the  constitution  of  this  system  in  view  of  its  special  functions.  It  is  this 
which  essentially  characterizes  the  grey  mat- 
ter of  the  ganglia  ;  the  ganglia  of  the  gi'eat 
sympathetic  are  nothing  more  than  one  of 
the  special  areas  of  this  substance,  attached 
to  its  other  areas  by  links  such  as  those 
which,  in  the  so-called  cerebro-spinal  mass, 
unite  the  grey  axis  of  the  cord  to  the  cerebral 
cortex.  It  would  be  of  the  highest  import- 
ance to  be  acquainted  with  the  laws, 
wliether  general  or  special  to  each  group, 
according  to  which  this  association  is  effected. 
There  is  still  very  little  known  abovit  it  : 
nevertheless,  experiment  has  fm'nished  some 
facts  which  are  of  an  interesting  natiii'e. 

Isolation  and  Dependence. — Observing  the 
ganglionic  chain  of  the  great  sympathetic, 
with  its  typical  and  regular  form,  its  situation 
outside  the  vertebral  column  andits  jwolonga- 
tions  to  the  visceral  organs,  one  is  tempted, 
by  exaggerating  somewhat  the  conception  of 
Bichat,  to  regard  it  as  an  independent  sys- 
tem, that  is  to  say,  one  whose  function  is  in- 
dependent of  that  of  the  rest  of  the  nervous 
system.  Experiment  has  refuted  in  different  ways  this  absolute  conception. 
The  influence  of  the  spinal  cord,  and  even  of  the  brain,  is  transmitted  to  the 
viscera  throvigh  the  great  sympathetic,  which  is  a  proof  of  a  somewhat  close 
bond  of  union  between  these  different  assemblages.  An  o})posite  opinion,  also 
obviouslj^  exaggerated  in  the  sense  of  simplicity,  would  regard  the  gi-eat  sympa- 
thetic as  an  ordinary  conductor  without  special  influence  on  the  impulses  which 
pass  through  iC  The  truth  is  that  the  great  sympathetic  represents  systematized 
groups,  connected  with  other  analogous  groups,  with  which  they  are  neither  con- 
stantly fused,  nor  from  which  constantly  isolated,  but  from  which  it  is  possible 
to  isolate  them  ;  the  Ijond  of  union  being  either  made  or  broken  according  to 
functional  necessities.  Experiment  shows  that  they  are  capable  of  isolation, 
by  manifesting  in  them  complex  nerve  acts, such  as  the  reflex  or  inhibitory  actions. 
In  the  normal  exercise  of  functions,  this  isolation  has  also,  at  certain  instants, 
its  raison  d'etre.  In  an  aggregate  so  essentially  mobile  as  the  living  being,  de- 
pendence or  independence  is  not  fixed  and  invariable,  but  is,  on  the  contrary, 
mobile,  contingent  and  gi'adviated. 

Study  by  degeneration. — The  method  of  Wallerien  degeneration  (degeneration 
after  section  of  the  segment  separated  from  the  nerve  cell  of  origin)  has  been 
made  use  of,  concurrently  with  the  ordinary  methods  of  experimental  physiology, 
in  order  to  study  the  connexions  of  the  sympathetic  ganglia,  either  with  other 

U  * 


Fig.  123. — Tliorac-ic  ganglion  of 
the  embryo  of  a  iowl  (after 
Cajal). 

A,  B,  cells  whose  axis  cylinders  sink 
in  the  cliain  CC  ;  E,  F,  protoplasmic 
prolongations  ;  G,  collaterals  ;  H,  ter- 
minal ramifications  of  the  axis  cylinders. 


296  SYSTEMATIC    FUNCTIONS 

centres,  or  between  themselves.  Schiff,  having  destroyed  in  birds  the  roots  of 
the  spinal  nerves,  found  degenerated  fibres  in  the  great  sympathetic  ;  he  natur- 
ally concluded  that  this  latter  has  its  origin  in  the  sj^inal  cord,  in  opposition  to 
the  views  of  those  who  located  it  in  the  ganglia. 

Once  again,  it  must  be  pointed  out  that  these  two  opinions  are  not  exclusi\-e 
the  one  of  the  other.  The  great  sympathetic  has  cells  of  origin  in  the  spinal  cord 
and  also  in  the  ganglia.  These  cells  are  the  place  of  origin  of  two  orders  of  neurons, 
the  one  superposed  on  the  other,  tvhich  transmit  the  impulse  to  the  ganglia  where 
their  junction  is  efjected.  To  make  use  of  a  comparison  which  renders  this 
arrangement  clear,  there  arc  motor  nerves  of  the  great  sjTiipathetic  as  there 
are  those  of  the  life  of  relation  ;  the  origins  of  these  latter  are  not  situated  totally 
and  exclusively  in  the  brain  or  in  the  spinal  cord  ;  they  are  in  the  cerebral 
cortex,  whence  arise  the  fibres  descending  to  the  grey  axis  of  the  cord,  and  they 
are  in  this  grey  axis  itself,  whence  the  impulse  retm-ns  to  proceed  to  the  muscles. 

In  the  one  as  in  the  other  case,  there  is  a  superior  and  inferior  neuron.  In 
that  which  is  known  as  the  great  sympathetic,  the  superior  neuron  commences 
in  a  cell  of  the  grey  medullary  matter.  According  to  Pierret,  this  origin  should 
be  found  in  the  tractus  intermedio-lateralis  (middle  horn),  a  species  of  third  horn 
interposed  between  the  two  others.  This  neuron  follows  the  communicating 
branches  and  terminates  in  some  ganglion.  The  inferior  neuron  commences  in 
a  cell  of  a  ganglion  and  proceeds  to  the  motor  or  secretory  element  for  which  it 
is  destined. 

The  great  sym2:)athetic  contains,  in  addition  to  the  ganglia  of  the  chain,  ter- 
minal plexuses  of  ganglionic  nature  (for  example  :  plexus  of  Auerbach  and  of 
Meissner  in  the  intestine,  the  oesophageal,  pharyngeal,  cardiac,  pulmonary 
plexus,  etc.,  etc.),  and  it  presents  as  well,  in  the  course  of  its  chief  branches  of 
distribution,  more  or  less  plexiform  ganglia  (for  example,  semi-lunar  ganglion 
and  solar  plexus). 

Between  these  ganglionic  masses  thus  scattered  from  the  vertebral 
column  to  the  viscera,  no  other  difference  so  far  has  been  noticed  than 
that  affecting  their  situation  ;  their  structure  and  function  are  the 
same,  so  far  as  is  known. 

Terminal  fibres  and  fibres  of  passage.— Are  all  these  ganglia  places  of  junction 
between  successive  neurons  ?  Yes,  in  the  sense  that  all  contain  cells  of  origin 
for  a  certain  number  of  neurons.  But  no,  in  the  sense  which  is  sometimes  im- 
plied, that  all  the  fibres  are  interrupted  in  all  tlie  ganglia,  and  that  there  would 
be  as  many  points  of  severance  as  of  ganglia  on  the  course  of  each  conductor. 
Histology  teaches  us  that  in  each  ganglion  there  are,  alongside  the  termi^ial 
fibres,  transitory  fibres,  that  is  to  say,  those  which  pass  on  without  stopping  in 
the  ganglion.  In  short,  for  a  given  fibre,  the  number  of  ganglia  placed  on  its 
covu"se  does  not  imply  the  number  of  points  of  severance  or  of  relays  which 
interrupt  it,  these  relays  being  effected  in  one  or  other  of  the  three  orders  of 
ganglia  indicated  above  (ganglia  of  the  sympathetic  chain,  terminal  ganglia, 
intermediate  ganglia).  This  point  cannot  be  determined  precisely,  all  that  can 
be  said  is  that,  from  the  cord  to  the  viscera  iJiere  is  at  least  one  interruption,  there- 
fore at  least  two  neurons  which  are  successive  or  superposed.  However,  the  tran- 
sitory fibres,  ichich  pass  through  the  ganglia  without  exhausting  their  terminal 
arborization  in  them,  usually  yield  up  to  them  some  collateral  branches,  which  still 
further  com23licates  tliis  structure,  but  which  helps  us  a  little  in  determining  its 
significance. 

By  this  means  a  given  fibre  (a  neuron  issuing  from  the  cord)  distributes  the 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    291 


impulse  to  several  terminal  fibres  (neurons  arising  from  different  ganglia).  The 
law  according  to  which  tliis  distribution  is  effected  is  vmknown,  both  as  regards 
the  great  syinpathetic  and  the  cord  ;  it  cannot  be  simple  inasmuch  as  it  repre- 
sents functions  neces- 
sarily coinjilex.  The 
associations  whicli  are 
effected  m  the  grey 
matter,  both  ganglionic 
and  spinal,  are  intended 
for  the  establishment 
of  different  and  multi- 
plied connexions,  a  sort 
of  conflict  between  the 
neurons  which  end  in 
tliis  grey  matter  and 
start  again  from  it, 
whence  results  a  trans- 
formation of  the  im- 
pulse wliicli  is  appro- 
priate to  the  functions 
to  be  fulfilled.  Very 
far  from  the  imjjulse 
passing  simpl^■  from 
one  fibre  to  the  follow- 
ing one,  the  field  of 
distribution  of  e^ery 
neuron,  from  its  origin 
to  its  termination,  must 
assuredly  be  very  com- 
plicated as  regards  its 
relations  with  preceding 
or  successive  neurons,  or 
even  with  collaterals. 


Mfiasnir's  Plprint. 


Fw. 


124. — The   interstitial   sympathetiL'   of  tiio   intestine 
(after  Ramon  y  Cajal). 
Section  of  two  villi  containing  nerve  cells  of  the  great  sym- 
pathetic. 


2.    The  grey  matter  of  the  ganglia  :  its  functions 

TJie  key  to  the  systematization  of  the  great  sympathetic  is  to  be 
found  in  the  constitution  of  its  gangha. 

Ganglia  ;  motor  nuclei. — These  gangha  are  motor  nucleL  or.  bettei'r 
seasori-motor.  Anatomically  the  origin  of  nerves  having  all  the  char- 
acters of  motor  nerves  is  found  in  them,  in  the  sense  that  the  neurons 
which  form  them  have  their  cells  ramified  in  these  ganglia  and  their 
axons  turned  towards  the  periphery.  The  terminations  of  axons  which 
come  from  above,  and  especially  from  the  spinal  cord,  are  also  to  be 
seen  in  them.  Physiologically  it  is  demonstrated  that  they  are  the 
localities  in  which  the  impulse  is  transformed.  They  may  stop  it, 
preserve  it,  redistribute  it  in  a  sort  of  way  to  organs  situated  in  their 
field  of  innervation  ;  each  of  them  resembles  a  segment  of  the  spinal 
cord.     These  essential  points  are  acquired  in  a  general  manner  :   much 


298  SYSTEMATIC    FUNCTIONS 

remains  to  be  done  as  regards  the  study  of  the  detail  of  these  functions 
and  the  locahzed  investigation  of  each  separate  ganghon. 

Their  experimental  isolation  from  the  Nervous  System. — As  regards  many  of 
the  great  sympathetic  ganglia,  their  motor  function  may  be  demonstrated,  but 
in  no  case  more  clearly  and  simply  than  in  those  of  tlie  heart.  In  this  case  a 
crucial  exijeriment  can  be  performed.  The  heart  of  a  cold-blooded  animal  is 
separated  by  cutting  the  vessels  which  keep  it  in  place  (the  vena  cava  and  the 
aorta?)  ;  it  is  seen  to  beat  with  regularity  for  a  considerable  time  ;  the  lower 
two-thirds  of  the  ventricle  are  separated  with  the  scissors  (the  portion  known 
as  tlie  apex)  ;  the  ventricular  portion  thus  detached  immediately  ceases  to  beat, 
while  the  pulsations  of  the  superior  portion  (the  am'icles)  continue. 

Artificial  circulation. — If  it  is  desired  to  render  the  experiment  still  more 
striking,  the  gaping  orifices  of  the  cut  vessels  are  sup])lied  with  glass  cannulas  ; 
these  are  j^rolonged  by  indiarubber  tubes  full  of  lilood,  in  such  a  way  as  to  main- 
tain an  artificial  circulation  in  the  heart.  The  latter  will  drive  the  blood  into  a 
reservoir,  whence  it  redescends  into  its  cavities,  and  this  circulation  may  con- 
tinue for  days  ;  but  if  the  physiological  continuity  of  its  nervous  network  be 
destroyed  by  a  ligature  aiDplied  a  little  below  the  base  of  the  ventricle,  the  heart 
stops  beating.  In  any  case,  the  conditions  which  maintain  this  movement, 
comparable  to  that  of  the  normal  circulation,  have  disappeared  ;  irregular  and 
intermittent  movements  alone  remain. 

The  heart  deprived  of  its  ganglia  is  thus,  at  the  first  glance,  reduced  to  the 
condition  of  an  ordinary  muscle.  It  contracts  if  it  is  stimulated,  but  only  when 
it  is  stinmlated  ;  except  at  the  moment  in  which  it  receives  the  stimulation,  it 
is  inert.  When  supplied  with  its  ganglia,  the  motor  organ  receives  stimuli  without 
our  supplying  any  to  it  :  deprived  of  its  ganglia,  it  ceases  to  receive  stimuli  unless 
u-e  ourselves  furnish  them.  How  can  these  ganglia  contain  a  provision  so  in- 
exhaustible that  it  can  last  for  fifteen  days,  as  has  been  observed  ?  That  these 
ganglia  have  ]ireserved  a  portion  of  those  impulses  whicli  have  come  from  the 
cord  by  the  cardiac  nerves  cannot  be  doubted  ;  but  that  they  have  been  reduced 
to  this  provision  made  in  advance,  seems  difficult  to  maintain.  Between  these 
ganglia  and  the  heart  muscles,  a  reflex  cycle  is  probably  established  whose  centri- 
petal paths  (from  the  muscle  to  the  ganglion)  are  unknown  to  us,  as  they  have 
remained  indistinguishable  up  to  the  present  time  amidst  the  other  nerves  ;  but 
it  appears  probable  that  they  exist  and  that  the  beating  of  the  heart  maintains 
the  stimulation  of  its  motor  nuclei  by  this  mechanism  at  once  reflex  and  auto- 
matic. 

Engelmann  and  Fano  incline,  it  is  true,  to  attribute  to  the  cardiac  muscle,  to 
the  exclusion  of  its  nervous  system,  the  avitomatism  of  these  cardiac  movements. 
It  must  be  admitted  with  them  that  the  question  is  still  enshrouded  in  obscvirity, 
but  it  cannot  be  allowed  that  they  have  demonstrated  that  this  automatism  is 
purely  muscular  in  the  adult  animal. 

In  the  isolated  stomach  of  the  frog  filled  with  a  liquid  alimentary  material, 
such  as  inilk,  an  experiment  of  the  sanie  natvire  can  be  carried  otit.  A  series  of 
periodical  contractions  act  on  the  liquid,  and  may  be  graphically  recorded.  The 
gall  bladder  acts  in  the  same  way,  as  Doyon  has  observed,  as  do  all  the  hollow 
muscles  furnished  with  ganglia. 

The  apex  of  the  heart.^The  apical  portion  of  the  heart,  that  which,  after  its 
separation  from  the  ganglia,  becomes  immobile,  has  been,  as  we  have  said,  com- 
pared to  an  ordinary  muscle  supplied  with  nerve  endings,  and  which  henceforth 
only  contracts  when  it  is  artificially  stimulated.  To  what  extent  is  this  com- 
parison exact  ?     It  is  precisely  here  that  new  researches  have  been  tmdertaken. 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION     299 

and  also  at  the  same  time  a  new  and  unexpected  direction  given  to  the  question 
of  the  n:iotor  mechanism  of  the  heart. 

Its  manner  of  reacting  to  stimuli. — In  reality,  viewed  from  certain  aspects 
which  it  remains  to  examine,  there  is  a  great  difference  between  the  reaction  of 
an  ordinaiy  muscle  to  a  varied  series  of  stimuli  and  that  of  this  inuscxtlar  seg- 
ment, which  is  currently  known  as  the  apex  of  the  heart.  The  ordinary  nuiscle 
follows  tolerably  faithfully  by  its  contractions  the  rhythm  of  the  stimuli  which 
are  supplied  to  it,  except  that  when  they  become  sufficiently  approximated  it 
unites  them  into  a  sustained  effort,  which  immobilizes  it  in  its  contraction,  wliich 
then  becomes  tetanic.  The  apex  of  the  heart  acts  rather  in  the  contrary  maimer  ; 
it  is  in  vain  that  the  rhythm  of  the  discharges  of  the  stimulating  alternate  current 
are  precipitated  upon  it  :  it  refuses  to  respond  to  these  stimuli  and,  after  having 
accelei'ated  its  action  up  to  a  certain  limit  (which  varies  according  to  the  in- 
tensity of  the  current),  it  continues  to  respond  by  dissociated  rhythmical  con- 
tractions ;  it  resists  tetanization  (Eckhard).  From  one  point  of  view  the  two 
objects  are  comparable  ;    from  another  they  are  not. 

Myogenous  and  neurogenous  doctrines. — The  rhythm,  the  automatism  of 
the  beats  of  the  heart  which  gives  such  a  special  physiognoniy  to  its  movements, 
would  not  then  have  its  explanation  in  the  special  organization  of  its  nervous 
sj'stem,  whether  intrinsic  or  extrinsic,  but,  on  the  contrary,  in  the  properties  of 
the  muscular  tissue  itself.  Hence  arise  two  doctrines  which  are  maintained  by 
physiologists  on  this  important  ]3oint  concerning  the  nervous  and  muscular 
function.  The  first,  faithful  to  the  ancient  conception,  are  the  neurogenists  : 
the  second,  partisans  of  the  new  explanation,  are  the  myogenists.  Both  oppose 
each  other  by  facts  whether  ancient  or  modern  ;  both,  in  order  to  suj^port  a 
definite  doctrine,  are  drawn  into  propping  it  up  with  hypotheses  of  which  the 
gratuitousness  or  the  spuriousness  alone  up  to  the  present  time  impress  the 
partisans  of  the  opposite  camp  ;  on  the  one  side  as  on  the  other  conviction  is 
complete.  We  will  describe  theSe  two  doctrines  as  briefly  as  possible,  but  also 
Impartiall}-. 

Undefined  paths  of  the  propagation  of  the  Impulse. — After  Fick,  Engelmann 
has  observed  that  if  a  ventricle  be  cut  in  a  zigzag  form,  the  impulse,  compelled 
to  follow  the  course  of  the  incision,  none  the  less  passes  from  one  extremity  to 
the  other  by  this  tortuous  route.  The  heart  is  composed  of  muscular  mono- 
cellular cells,  which  are  often  branched  and  welded  together  by  a  cement  {trait 
scalifonne)  at  their  extremities  ;  thus  these  cells  transmit  the  impulse  from  one 
to  the  other.  It  was  originally  thouglit  that  this  muscular  network  of  welded 
cells  contained  no  nerve  fibre  :  and  the  myogenous  theory  found  in  this  fact  a 
conclusive  proof  of  its  accuracy.  Ranvier  was  the  first  to  ascertain  the  existence 
of  a  very  fine  network,  lining  the  joreceding,  a  netM'ork  the  existence  of  which 
is  rendered  very  obvious  by  the  employment  of  the  cliromate  of  silver  method. 
Deprived  of  this  argument,  the  myogenists  have  foiind  another  of  the  same 
order  in  the  facts  furnished  by  comparative  anatomy  and  embryology. 

Movements  of  the  heart  in  the  embryo. — Fano,  Pattrizzi,  and  Pickering  have 
obser\'ed  that  in  the  embryo  of  the  fowl  the  heart  commences  to  beat  not  only 
before  any  nervous,  but  even  any  distinct  muscular  element  can  be  distingviished. 
This  is  certainly  a  fact  of  the  highest  importance  as  regards  the  origin  of  the 
rhythm  and  of  the  automatism  of  the  heart,  whatever  may  be  the  solution  of 
the  question  under  discussion,  whether  for,  against,  or  apart  from  myogeny  or 
neurogeny.  It  is  true  that  this  information  does  not  solve  the  problem,  but 
rather  brings  forward  a  new  one,  namely,  in  a  mass  of  homogenous  protoplasm, 
manifesting  the  simplest  functions  of  the  adult  heart,  what  is  it  which  represents 
the  muscle  and  what  the  nerves  ?  The  myogenists  maintain  as  obvious  that 
the   muscle  alone  is  represented,  and  that  nerves  will  appear  later  at  a  certain 


300  SYSTEMATIC    FUNCTIONS 

period  of  development.  The  neurogenists  ask  if  our  present  metliods  of  histo- 
logical technique  allow  of  otir  grasping  a  commencing  differentiation  ;  and  if, 
with  the  improvements  which  they  will  undergo  in  futiire,  the  negative  informa- 
tion concerning  the  embryonic  heart  will  not  have  the  same  fate  as  that  which 
was  at  first  accepted  for  the  adult  heart  ;  till  recently  it  was  not  possible  to 
distinguish  nerve  elements  which  are  now  easily  demonstrated. 

Excitability  and  conductivity. — The  contraction  of  the  heart  is  at  the  same 
time  rhythmical  and  peristaltic.  It  arises  in  one  area,  starting  from  which  it 
is  propagated  to  other  areas,  like  a  wave  changing  its  place.  How  is  the  com- 
munication of  the  impulse  effected  in  this  succession  of  cells  welded  together 
by  their  extremities  ?  The  myogenists  maintain  that,  tlirovigh  the  connecting 
inaterial  of  these  weldings,  the  sarcoplasm  (not  the  myoplasm)  of  the  muscular 
cells  is  continuous  from  the  one  to  the  other.  According  to  them,  the  conduc- 
tivity and  the  excitability  of  the  muscular  tissue  would  be  two  distinct  things, 
the  first  localized  in  the  sarcoplasm  (primitive  or  organotrophic  protoplasm  of 
the  cell),  and  the  second  in  the  myoplasm  (differentiated  protoplasm).  Thus 
would  be  explained,  as  regards  the  myogenists,  how  it  is  that  the  wave  of  con- 
traction, arising  in  one  point,  is  sometimes  propagated  to  remote  points  without 
affecting  the  intermediate  area  which  remains  in  repose.  The  neurogenists 
object  that  the  fact  of  propagation  of  the  impulse,  without  visible  movement, 
belongs  particular!}-  to  nerves,  and  that  there  is  no  need  to  reject  this  explana- 
tion when  it  is  a  question  of  an  organ  like  the  heart,  wliicli  is  abiindantly  pro\'ided 
with  nerves.  It  may  be  remarked,  on  the  other  hand,  that  the  partitions  between 
successive  cells  appear  to  be  very  complete,  since  they  hinder  in  the  heart  the 
so-called  current  of  demarcation  or  alteration,  which  in  other  muscles  arises 
on  their  cut  siu-face  and  persists  vip  to  the  entire  destriiction  of  the  luuscle,  thanks 
to  the  non-discontinuity  of  the  latter  (muscle  of  the  .skeleton). 

The  neurogenists  maintain  that  the  muscvilar  element  of  the  heart  is  absolutely 
inexcitable  in  a  direct  manner,  and  that  every  stimulus  is  conveyed  to  it  through 
the  nerves.  This  may  also  seem  to  be  an  exaggerated  statement  when  it  is 
remembered  that,  wherever  a  division  occurs  between  nervous  and  muscular 
tissues,  the  mviscle  shows  an  excital^ility  peculiar  to  itself.  In  truth,  no  stimula- 
tion is  so  efficient  for  it  as  that  which  it  receives  from  its  nerve.  In  the  case  of 
the  heart  we  have  no  means  of  dissociation,  because  its  nerves  are  found  to  be 
refractory  to  the  action  of  curare.  In  any  case,  curare  does  not  paralyse  the 
cardiac  movements. 

So  far  as  regards  the  propagation  of  the  impulse  from  one  portion  of  the  heart 
to  another,  facts  are  already  in  existence  which  show  tliat  the  auricle  sometimes 
possesses  a  rhythm  independent  of  that  of  the  ventricle  (Chauveau).  Fvirther, 
this  independence  can  be  obtained  by  section  of  certain  nerve  filaments  which 
are  visible  on  the  surface  of  the  heart  (Nadine,  Lomakine). 

Periodic  inexcitability ;  Refractory  phase ;  Compensatory  repose, — Peristalt- 
ism  is  the  proi)agatioh  of  the  wav^e  of  contraction  ;  rhythm  is  its  periodical  re- 
production in  the  same  place  at  each  point  of  its  com'se  under  consideration. 
This  periodicity  is,  as  it  were,  the  result  of  the  incapacity  of  the  heart  to  fuse 
together  its  contractions,  a  consequence  of  that  which  we  have  called  its  resist- 
ance to  tetanization.  As  Marey  has  observed,  during  the  active  jahase  (systolic 
period  of  its  contraction)  it  is  refractory  to  every  new  or  supplementary  stimulus  ; 
during  the  diastolic  period  (that  is  to  say,  the  period  of  loss  of  contraction)  and 
the  pause  which  follows  it,  it  again  becomes  capable  of  stimulation.  If  the 
stimulus  occurs  in  this  diastolic  period  or  during  the  pause,  it  gives  rise  to  systole 
out  of  turn  (extra-systole).  But  if  this  unrhythmical  systole  somewhat  deranges 
the  order  of  the  contractions  it  does  not  alter  the  number  of  them,  because  it  is 
followed  by  a  compensatory  repose.     The  stimulus  lias  only  anticipated  tlie 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    301 

coiiitraction  wliich  sliould  follow.  The  work  of  the  heart  remains  constant.  The 
fact  of  periodical  inexcitability  of  the  systolic  phase  is  very  real  and  evident  ; 
how  is  it  to  be  explained  ?  And  is  it  to  be  attributed  to  the  muscle  or  the  nerve  ? 
The  response  may  be  foreseen  according  to  the  general  theory  accepted.  For 
the  myogenists  it  l^elongs  to  the  muscle,  for  the  neurogenists  the  complexity 
of  the  conditions  which  take  part  in  it  seems  a  clear  indication  of  its  belonging 
to  the  ner\'ous  system. 

Point  of  departure  of  the  stimulus. — The  point  of  departm-e  of  tlie  systolic 
contraction  is  in  the  sinus  venosus  and  tlie  auricle,  wlience  the  movement  passes 
on  to  the  ventricle.  From  the  auricle  to  the  ventricle  it  has  been  long  thought 
that  the  passage  could  only  be  effected  by  means  of  nerve  elements  which  proceed 
from  one  to  the  other.  His,  junior,  having  foimd  that  between  the  two  a  small 
bridge  of  muscular  substance  exists,  the  myogenists  interpreted  this  fact  in 
favoxir  of  the  possibility  of  a  transmission  effected  only  by  the  muscular  substance. 

But  the  heart  is  double,  and  if,  in  the  inferior  vertebrata,  it  only  contains  one 
ventricle,  it  possesses  two  auricles,  in  which  terminate,  in  one  the  vena  cava,  in 
the  other  the  pulmonary  veins,  which  are  distinctly  separated  A-essels. 

It  is  from  these  very  distinct  regions  that  a  double  wave  of  contraction  arises, 
of  which  the  two  courses,  at  first  independent,  finally  converge  on  it  or  the  ven 
tricles.     How  can  it  be  maintained,  object  the  neurogenists,  that,  without  the 
intervention  of  the  nervous  system,  the  muscles,  separated  at  this  point,  can  act 
so  unanimously  at  the  point  of  departiu-e  of  the  systole  itself  ?  (Hering.) 

First  origin  of  the  stimulus. — Thus;  for  the  myogenists,  the  rhythm,  the  peris- 
taltisni,  in  a  word,  the  particular  form  of  the  motor  reaction  of  the  heart,  is  a 
pvu'ely  muscular  phenomenon.  But  whence  come  the  stimuli  '?  This  is  a  doubtful 
point  for  them  ;  but,  they  say,  with  sufficient  probability  it  may  be  allowed, 
"that  the  stimuli  do  not  take  their  origin  in  the  ganglionic  nerve  elements,  but 
rather  in  muscular  elements  which  are  histologically  but  little  differentiated, 
.  .  .  they  are  ^^ery  probably  the  expression  of  the  automatic  disintegration  of 
the  living  substance  of  a  more  or  less  extensive  group  of  muscular  cells,  situated 
at  the  venous  extremity  of  the  cardiac  tube."  This  time,  the  nervous  system 
is  dispossessed  of  the  most  fundamental  and  most  essential  property  of  those 
which  vip  to  the  present  time  have  been  recognized  in  it,  that  of  being  an  organ 
of  stimulation  for  the  other  tissues.  The  cardiac  muscle  would  not  therefore 
owe  its  stimulus  either  to  the  blood  or  to  the  nerves  ;  it  would  supply  it  to  itself  ; 
bj^  its  own  contractions  it  would  be  stimulated.  Contraction  and  stimvilation 
would  thus  be  mutually  related  the  one  to  the  other,  being,  as  they  would  be, 
bound  together  in  an  intramuscular,  intracellular  cycle.  Such  an  exclusive 
opinion  as  this  is  not,  howe^'er,  that  of  all  the  joartisans  of  the  myogenous  theory. 

It  caiuaot  be  allowed  that  the  cardiac  muscle  receives  the  stimulus  otherwise 
than  by  its  nervous  system.  When  the  ganglia  are  intact,  it  is  they  which  supply 
the  impulse  ;  when  they  are  remo^^ed  and  when  the  apex  of  the  organ  is  elec- 
trically stimulated,  it  is  its  nerves  rather  than  its  muscles  which  receive  this 
artificial  stimulation,  and  this  in  the  same  manner  as  an  ordinary  muscle.  But — 
and  in  this  it  differs  from  an  ordinary  muscle — the  effect  of  the  stimulation  is 
inxariably  rhymthical,  that  is  to  saj*,  interrupted  by  intervals  of  repose ;  and 
peristaltic,  that  is  to  say,  slowly  propagated.  The  origin  of  the  impulse  being 
undeniably  in  the  nerves,  is  the  form  which  it  assumes  and  wliich  it  impresses  on 
the  movement  due  to  the  nerves  or  rather  to  the  cardiac  muscle  ?  In  order  to 
form  an  opinion,  it  is  necessary  to  re-examine  the  three  phenomena  wliich  we 
have  described  as  periodic  inexcitability  of  the  heart,  the  extra-systole  and  the 
compensatory  repose,  in  condensing  as  much  as  possible  the  conditions  of  their 
production. 

Mechanism  of  the  periodic  inexcitability. — During  the  systolic  phase  of  its 


302  SYSTEMATIC    FUNCTIONS 

conti-action,  the  heart  is  inexcitable.^  As  tliis  systoUc  phase  recurs  periodically 
this  inexcitability  would  also  occiu-  periodically.  If  the  separated  apex  of  the 
heart  be  artificially  stimulated  by  the  aid  of  discharges  possessing  tlie  normal 
rhythm  of  the  heart,  every  superadded  stimulation  falling  on  the  systolic  phase 
will  be  without  effect.  But  every  stimulation  falling  apart  from  this  phase 
might  produce  an  extra-systole.  The  rhythmical  discharges  supplied  to  the 
apex  of  the  heart  here  seem  to  replace,  purely  and  simply,  the  stimuli  supplied 
normally  by  the  sinus  venosus  (ganglia)  ;  the  intercalated  stimulus  so  far  as 
concerns  them  behaves  in  the  same  way  as  it  does  with  regard  to  the  normal 
stimuli  starting  from  the  sinus.  If,  instead  of  giving  to  the  stimvilating  charges- 
the  normal  rhythm  of  the  heart,  they  are  rendered  more  and  more  frequent, 
the  apex  of  the  heart  will  at  first  follow  this  new  rhytlim  ;  but  the  systoles  being 
more  and  more  apj)roximated,  the  phases  of  inexcitability  will  be  the  same. 
When  they  coincide,  it  will  necessarily  follow  that  the  stimuli  will  be  without 
result ;  only  those  will  be  efificacious  which  are  not  synclironous  with  the  systolic 
phase  of  subsisting  contractions.  Thus  is  explained,  by  means  of  systolic 
inexcitability,  the  fact  that  the  contraction  of  the  heart  is  always  rhythmical  ; 
or,  as  has  already  been  said,  that  this  organ  resists  tetanization. 

There  is,  nevertheless,  a  condition  which  may  in  a  certain  degree  coimteract 
this  inexcitability,  this  is  the  intensity  given  to  the  stimulus.  It  may  shorten 
the  phase  of  inexcitability  ;  very  strong  intercalated  stimulation  may  give 
origin  to  an  extra-systole  in  case  a  ir.ore  feeble  one  should  not  arrive.  This  is 
at  least  the  opinion  of  Marey  and  of  Dastre,  contrary  to  that  of  Engelmann,  who 
denies  this  influence  of  intensity. 

We  see  clearly  that  the  nem'o-muscular  organ  refuses  the  stimulation  at  a 
certain  moment  which  we  are  able  to  define  (period  of  activity),  and  accepts  it 
at  certain  others  (period  of  repose)  ;  and  this  is  the  first  datum  from  which  we 
start  in  order  to  explain  the  greater  number  of  the  facts  peculiar  to  the  heart. 
Fundamentally,  this  result  is  inexplicable.  We  only  endeavour  to  find  out  to 
what  tissue  it  belongs.  But  nothing  exactly  indicates  to  us  that  this  refusal 
as  regards  stimulation  is  peculiar  to  muscle  or  nerve.  Thus  the  periodic  excita- 
bility may  appertain  either  to  the  first  or  to  the  second.  It  remains  to  inquire 
into  the  compensatory  repose  and  the  constancy  of  the  work  of  the  heart  which 
appear  to  be  the  consequence  of  it. 

Mechanism  of  compensatory  repose. — Dastre  was  the  first  to  ask  the  question 
whetlier  tliis  phenomenon  will  be  observed  by  stimulating  the  apex  of  the  ven- 
tricle, or  whether  it  appertains  only  to  the  heart  fvu-nished  with  its  ganglia,  in 
which  case  it  would  obviously  be  of  nervous  origin.  We  have  seen  above  in 
what  it  consists.  The  extra-systole  which  is  produced  by  irritating  the  whole 
heart  in  the  diastolic  phase  is  not  a  supernumerary  systole,  it  is  only  an  anticipated 
systole  ;  a  compensatory  repose  rej^laces  the  following  sj'stole  in  its  normal 
place  and  the  work  of  the  lieart  remains  constant.  On  the  other  hand,  the  extra- 
systole  which  is  provoked  by  stimulating  the  apex  of  the  heart,  when  a  stimvilus 
is  intercalated  out  of  turn  in  the  interval  between  the  contractions,  is  not,  accord- 
ing to  Dastre,  followed  by  a  compensatory  repose.  This  latter,  therefore,  would 
be  of  ganglionic  origin.  Gley  has  also  determined  the  existence  of  this  pheno- 
menon in  the  heart  of  warm-blooded  animals.  Later,  Kaiser  has  arrived  at  the 
same  conclusion.  On  the  other  hand,  Engelmann  has  endeavoured  to  diminish 
the  value  of  these  facts.     According  to  him,  the  more  or  less  prolonged  repose 

1  More  accurately,  the  inexcitability  commences  O**"!  before  the  commencement  of 
the  systole  and  finishes  O""^'-'  'l  before  its  end.  This  delay  of  0'*'"=  1  corresponds  to  a  latent 
period.  This  is  equivalent  to  saying  that  the  mechanical  phenomena  of  the  contraction 
are  retarded  by  O^'^'^-l  as  regards  the  chemical  phenomena  which  develop  the  energy 
necessary  to  its  performance.  The  inexcitabihty  exactly  corresponds  with  the  chemical 
phenomena  of  the  systolic  phase. 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    303 


Auric. -plex. 

Fig.    125. — The  cardiac  plexuses  in  the  human  embryo  (after 
W.  His,  junior). 


which  (in  the  case  of  the  entire  heart)  follows  the  extra-systole  has  not  a  really 
compensatory  value,  but  is  dvie  only  to  the  fact  that  the  extra-systole  is  followed 
by  a  phase  of  inexcitability  which  annuls  the  effect  of  the  impulse  descending 
at  this  instant  from  the  sinus  and  the  auricles.  If,  says  he,  two  extra-systoles 
are  produced  one  after  the  other,  the  following  systole  will  not  be  repulsed  two 
degrees,  but  only  one  degree  ;  whatever  may  be  the  number  of  extra-sj^stoles, 
the  consecutive  repose  remains  the  same. 

The  nervous  Network  of  the  apex  of  the  heart. — If  the  nervous  origin  of  cardiac 
excitation  cannot  be  denied,  it  must  be  remembered  that,  so  far  as  concerns  the 
special  rhythmical 

form  of    the    con-  Aorta  ("^  f^"^^^-     Symp. 

traction  which 
fo  11  o  w  s,  there 
may  be  hesitation 
as  to  whether  it 
should  be  c  o  n  - 
nected  with  the 
muscular  or  ner- 
vous tissue.  Cer- 
tain facts,  how- 
ever, seem  rather 
to  attribute  it  to 
this  latter.  The 
apex  of  the  heart 
is  not  exactly 
comparable  to  an 
ordinary  muscle 
supplied   with   its 

nerve  terminations.  The  nervous  network  which  anatomy  reveals  in  it  displays  a 
complication  which  these  latter  certainly  do  not  possess  to  the  same  degree. 
Separated  from  the  ganglia,  properly  so  called,  to  which  appertains  the  co-ordinat- 
ing fimction  of  the  cardiac  contraction,  this  network  still  manifests  to  a  certain 
degree  their  functions  and  properties.  Sometimes,  indeed,  it  appears  to  com- 
pletely supplement  them  ;  this  occm-s  when  the  section  separating  the  ventricle 
from  the  auricle  is  effected  very  high  up,  immediately  below  the  lowest  group 
of  the  ganglionic  cells.  It  may  then  happen  that  the  ventricle,  placed  in  favour- 
able conditions,  may  begin  to  beat  spontaneously.  The  organization  of  the 
excitation,  its  regular  maintenance,  would  then  be  less  the  result  of  the  ganglionic 
cells  themselves  than  of  the  associations  which  their  prolongations  effect.  In 
brief,  the  properties  attributed  to  the  ganglia  would  be  rather  those  of  the  net- 
work which  t-ekes  origin  in  them  (Morat). 

Its  complexity. — The  difference  between  the  apex  of  the  heart  and  an  ordinary- 
muscle  consists  especially  in  this,  that  in  the  latter  the  nerve  terminations  are 
simple  conductors  depri\ed  of  any  special  arrangement  by  which  they  are  united 
amongst  themselves  ;  while  in  the  first,  these  terminations  are  systematized  in 
such  a  way  as  to  impress  on  the  impulse  numerous  and  verj^  deep  transformations, 
WTaile  in  the  case  of  a  skeletal  muscle  the  conflict  of  nervous  actions  of  diverse 
sorts,  which  must  determine  the  form  of  its  movement,  is  carried  on  in  the  grey 
matter  of  the  spinal  cord,  in  the  cardiac  muscle  this  conflict  between  different 
nerve  elements  occurs  in  immediate  contact  with  the  muscular  substance,  and 
this  is  without  doubt  the  reason  why  this  special  muscle  seems  to  be  so  markedly 
different  from  all  others.  ^ 

1  The  intestine  and  a  nimiber  of  organs  of  vegetative  life  in  this  respect  much  resemble 
the  heart.     The  mesenteric  plexus  is  in  direct  contact  with  the  muscles  of  the  intestine. 


304  SYSTEMATIC    FUNCTIONS 

Its  different  origins. — The  fibres  which  foi'in  the  nervovis  network  of  the  apex 
of  the  heart  certainly  arise  in  large  proportion  from  the  ganglionic  cells  situated 
at  the  base  of  the  organ.  They  are  the  axons  of  these  ganglionic  cells,  a  species 
of  very  short  peripheral  neixrons,  which  are,  as  has  just  been  said,  co-ordinated 
into  a  small  system  which  is  callable  of  automatic  autonomous  functional  activity. 
In  these  ganglionic  cells  the  terminations  of  the  fibres  of  the  great  sympathetic 
and  of  the  branches  of  the  vagus  destined  for  the  heart  come  to  an  end,  forming 
as  they  do,  above  the  first,  an  exciting  and  regulating  system  of  movement,  a 
sj'stem  of  neurons  of  the  second  order.  Some  authors  nevertheless  maintain 
that  the  network  of  the  apex  of  the  heart  may  contain  fibres  arising  either  from 
the  vagus  or  from  the  great  sympathetic,  and  it  may  be  allowed  that  this  is  so 
without  any  infringement  of  the  general  law  which  expresses  the  relationship 
of  the  deep  and  peripheral  nem-ons. 

It  is  known,  indeed,  that  the  plane  of  separation  between  the  first  and  the 
second  does  not  reside  usually  in  a  single  mass  or  in  a  single  ganglionic  group, 
but  exists  at  the  same  time  in  the  majority  of  the  ganglions  arranged  in  graduated 
series  in  the  coirrse  of  the  nerves  proceeding  from  the  cord  and  from  the  bulb,  in 
such  a  wav  that,  side  by  side,  with  short  peripheral  neurons  (cells  situated  in 
the  heart),  there  are  long  peripheral  neurons  (whose  cells  of  origin  are  situated 
in  the  symjjathetic  chain  or  in  the  vagus).  On  the  other  hand,  so  far  as  specially 
concerns  the  cardiac  ganglia,  the  siu-face  of  separation  between  the  peripheral 
and  deep  neurons  is  not  necessarily  in  the  immediate  neighbourliood  of  the  gang- 
lionic cells,  but  may  be  found  represented  in  the  ner^'ous  network  wiiich  emanates 
from  them  very  near  the  muscular  element. 

Anodic  stimulation  :  its  inhibitory  effect. — In  the  manner  in  which  it  responds 
to  stimuJi,  the  heart  also  presents  the  following  peculiarity  noticed  by  Bieder- 
mann.  Let  a  ventricle  containing  blood  whose  pressure  upon  its  walls  is  moder- 
ate be  taken.^  The  ventricle  is  stimvilated  by  the  unipolar  method  ;  that  is  to 
say,  one  of  the  poles  of  the  circuit  of  the  battery  being  jilaced  on  the  body  of 
the  animal  (frog,  tiu-tle),  the  other  pole  is  placed  in  contact  with  the  apex  of 
the  heart.  The  resulting  effect  is  not  only  different,  but  is  inverted,  according 
to  the  nature  of  the  pole  which  touches  the  ventricle.  If  this  is  the  negative 
]3ole  (cathode)  the  locally  stimulated  portion  contracts  according  to  the  well- 
known  law  which  has  been  established  by  the  observations  of  Chauveau  ;  if  it  is 
the  positive  pole  (anode),  the  locally  stinmlated  portion  becomes  distended  by 
the  pressure  of  the  blood.  It  must  be  admitted  that  before  any  action  of  the 
stimulating  cvirrent  the  ventricle  was  in  a  state  of  tonus  ;  the  action  of  the  nega- 
tive pole  or  cathodic  stimulation  has  increased  this  tonus,  the  action  of  the 
positive  pole  or  anodic  action  has  diminished  it. 

Antitonic  action  of  the  vagus  nerves. — The  diminution  of  tonus  which  thus 
results  from  anodic  excitation  has  been  very  naturally  regarded  as  an  inhibitory 
phenomenon,  and  this  so  much  the  more  as  the  stimulation  of  the  vagus  may 
give  rise  to  altogether  analogous  results,  though  generalized  in  the  heart  as  a 
whole.  If  in  the  tvirtle  one  of  the  vagus  nerA-es  is  stimulated  in  the  neck,  the 
intensity  being  just  sufficient  to  ^^roduce  arrest  of  the  \'entricular  contraction, 
and  if,  during  this  arrest,  the  vagus  of  the  other  side  be  stimulated,  the  line  of 
traeinCT  on  the  right  side  will  fall  slightly  below  its  primitive  level  and  will  thus 

1  Immobility  of  the  apex  of  the  heart  is  obtained  by  its  physiological  separaiion  from 
the  rest  of  the  organ.  It  is  not  necessary  that  this  separation  be  effected  in  the  mechani- 
cal sense  of  the  word.  It  can  be  obtained  by  placing  a  ligature  tied  round  the  upper 
part  of  the  ventricle,  in  wliich  a  camiula  has  been  placed  and  on  wliich  the  constriction 
of  the  ligature  acts.  This  camiula  is  in  general  communication  with  a  tube  filled  with 
blood,  or  with  serum  playing  the  part  of  a  manometer. 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    305 


remain  during  this  double  stimulation.     This  is  a  device  for  rendering  evident 
the  antitonic  action  of  the  pnemnogastric  (Dastre  and  Morat). 

The  inhibitory  action  of  anodic  excitation  applied  directly  to  the  ventricle 
is  differently  interpreted  according  to  the  views  of  the  observer.  For  a  thorough- 
going mj'ogenist,  the  action  is  exerted  on  the  muscle  itself.  For  the  neiiro- 
genists,  it  affects  the  nervous  tissue  ;  but  it  may  be  differently  interpreted  accord- 
ing to  whether  it  is  maintained  that  the  fibres  of  the  vagus  have  a  direct 
inhibitorj-  influence  on  the  cardiac  muscle,  or  whether  these  fibres  are  regarded 
as  exercising  their  inliibitory  action  on  the  tonic  stimulation  distributed  tO' 
the  muscle  by  the  intraventricular  nervous  network.  This  network  is,  indeed, 
complicated,  and  it  is  justifiable  to  conceive  it  as  formed  of  elements  acting 
the  one  on  tlie  other,  or  the  one  by  the  intermediation  of  the  other. 

Conclusion. — In  brief,  if  certain  facts  of  gi-eat  importance  are  put  on  one  side, 
such  as  the  loss  of  motor  spontaneity  in  the  portions  of  the  heart  separated  from 
the  ganglionic  apparatus,  it  is  seen  that,  whatever  interest  attached  to  the 
numerous  discoveries  concerning  details  which  have  been  made  in  seeking  to. 
investigate  the  niechanism  of  the 
cardiac  motricity,  none  has  a 
really  decisi\e  value  as  regards 
the  solution  of  this  problem. 
The  functions  of  the  muscle  and 
of  tlie  nerves  continue  in  some 
degi-ee  indissociable  by  our  pre- 
sent means  of  analysis.  Conse- 
quently the  arguments  drawn 
from  analogy  with  other  motor 
systems  in  which  dissociation  is 
possible  and  even  easy,  ha^e  a 
great  influence.  They  manifestly 
plead  in  favour  of  an  explanation 
which  as  a  whole  is  practically 
neurogenistic. 

Functional  role  of    the  differ- 
ent   ganglia    of    the    heart. — In 
their  totality,  the  cardiac  ganglia 
have  a   motor  action    as    regards 
not    the    same    for   all 


Lu, 


Y\v,.    126. — Ganglia  of  the  Iieart  in  the  frog. 

OD,  OG,  right  and  left  auricles  :  V,  single  ventricle  r 
Sin,  sinus  venosus  ;  gg,Re,  ganglion  of  Remak  ;  gg.B, 
ganglion  of  Bidder  ;    gg.Lu,  ganglion  of  Ludvrig. 


the  heart.  Their  isolated  functions  are 
Situated,  the  one  in  the  sinus  venosus  (ganglion  of 
Remak),  the  other  in  the  interam-icular  partition  (ganglion  of  (Ludwig),  the 
third  in  the  aiu'iculo-ventricular  partition  and  the  upper  portion  of  the  ventricle 
(ganglion  of  Bidder),  they  are  adapted  for  experiiuent  involving  their  separation 
or  isolation.  Jf  a  ligature  be  placed  at  the  line  of  separation  of  the  sinus  venosus- 
and  the  auricles,  the  heart  immediately  stops  beating  ;  this  stoppage  may  last 
for  a  quarter  of  an  hour  or  twenty  minutes,  then  the  beats  recommence.  This 
is  the  exjaeriment  knowii  as  that  of  Stannius.  It  is  one  of  the  most  significant 
of  the  numerous  ligatvu'e  experiments  which  this  observer  has  performed  in  thi* 
kind  of  research. 

It  has  been  disputed  as  to  whether  this  ligature  acts  as  a  blocking  effected  in 
the  intracardiac  nervous  system,  or  by  stimulating  certain  portions  of  the  latter. 
In  other  words,  does  it  suppress  excito-motor  centres  ?  Or  does  it  stimulate 
moderating  centres  or  nerves  ?  The  two  opinions  are  not  exclusive  the  one  of 
the  other.  The  ganglion  of  Remak  is  situated  in  the  locality  in  which  the  wave 
of  heart  contraction  arises.  It  is  this  ganglion  doubtless  which  sujaplies  the 
initial  stimulation  wlience  this  contraction  proceeds.  If  it  be  tlirowii  out  of 
action,  the  two  other  ganglia  remain  for  a  time  insufficient  to  give  rise  to  new 

P.  X 


'306 


SYSTEMATIC    FUNCTIONS 


Fig.    127. — Ligatures  of  Stannius. 

L,  site  of  the  ligatuie  ;  1,  auricle  ;  2,  ventricle  ; 
■3,  sinus  venosus. 

Fig.  on  the  left  :  ligature  at  the  boundary  of 
the  sinus  producing  stoppage  of  the  heart  beats 
for  some  minutes. 

Fig.  on  the  right  :  second  ligature  applied  after 
the  first  causing  reappearance  of  the  beats. 


contractions.  And  tliis  so  much  tlie  more  as  the  ganglia  of  Bidder  and  of  Ludwig 
appear  to  have  a  reciprocally  antagonistic  influence  ;  the  first  being  regarded 
as  especially  excito-motor,  the  second  as  especially  inhibitory. 

If,  while  the  heart  has  stopped  beating  through  tlie  apjolication  of  the  first 
ligatm-e  of  Stannius,  a  second  be  applied  at  the  boundary  line  between  the  auricle 
and  the  ventricle,  the  heart  also  is  seen  to  i-espond.  Is  the  recommencement 
•of  the  beats  due  to  the  svippression  of  the  inhibitory  action  of  the  first  ligature  ; 
to  the  suppression  of  the  inhibitory  action  of  Ludwig's  ganglion  ;  to  the  direct 
istimulation  of  Bidder's  ganglion? 

It  is  probable  that  all  these  influ- 
ences act  at  the  same  time  There 
are  different  ways  of  proving  that 
Bidder's  ganglion  is  especially 
excito-motor  ;  on  the  other  hand, 
by  directly  stimulating  I.udwig's 
ganglion  through  the  thickness  of 
the  interaiiricular  septum,  stoppage 
of  the  heart  results. 

Reflex  function. — It  is  invariably 
the  case 'that,  while  the  heart  is 
stopped  by  the  first  ligatvire,  if  the 
ventricle  be  lightly  touched,  it  is 
observed  to  contract.  Bidder,  who 
was  the  first  to  perform  this  ex|)eri- 
ment,  regarded  it  as  a  movement 
of  reflex  nature  wliose  centre  of 
I'eflection  would  be  situated  in  the 
still  intact  ganglia.  On  account  of  its  sjiecial  position  in  the  depth  of  the 
muscular  tissue,  the  intracardiac  nervous  system  is  little  adapted  for  the 
demonstration  of  the  reflex  power  of  the  ganglia  ;  but  there  is  no  doubt  that 
this  power  exists  in  it. 

Division  of  attributes. — According  toCyon,  the  functions  of  the  three  23i'incipal 
ganglia  are  as  follows  :  situated  at  the  point  of  departure  of  the  wave  of  cardiac 
contraction,  the  ganglion  of  Rcmak  would  control  in  the  first  place  the  frequency 
of  the  heart-beats  ;  placed  immediately  above  the  ventricle  and  being  prolonged 
into  it  by  cells  disseininated  in  its  ii2:)per  portion,  the  ganglion  of  Bidder  would 
give  rise  above  all  to  the  force  of  the  contraction  ;  as  to  the  totality  of  cells  which 
in  the  interauricular  wall  forms  what  is  known  as  the  ganglion  of  Ludwig,  it 
would  possess  a  regulative  function  both  as  regards  the  frequency  and  the  strength 
of  the  heart  beats,  and  consequently  would  regulate  the  activity  of  the  other 
heart  ganglia. 

Although  these  details,  both  anatomical  and  functional,  have  been  more  especi- 
ally demonstrated  in  the  heart  of  the  frog,  they  are  equally  applicable  to  mam- 
mals, in  which  are  found  the  more  or  less  complicated  equivalents  of  the  preced- 
ing organs  and  of  their  special  functions.  Experiments  analogous  to  all  the 
preceding  may  be  performed  in  them,  on  the  condition  that  the  properties  of  the 
tissues  are  maintained  by  artificial  circulation  ;  experiments,  it  is  true,  which 
are  more  difficult  to  carry  out  in  the  mammalian  heart,  on  account  of  its  inter- 
stitial circulation.  Newel]  Martin  and  Langendorff  have  demonstrated  circula- 
tions of  this  kind,  confined  to  the  heart  itself,  in  the  superior  animals. 

Action  of  oxygen  on  the  movements  of  the  heart. — If  the  movements  of  the 
heart  depend  on  its  ganglia,  these  latter  in  their  turn  depend  on  a  number  of 
conditions  which  influence  their  excitability.  It  is  necessary  to  consider  especi- 
ally the  gaseous  condition  of  the  blood  and  its  temperature.     These  conditions 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    307 

certainly  act  ont  he  muscle  and  on  its  nerves,  luit  primarily  and  energetically 
on  these  latter. 

Tlie  influence  of  ox^^gen  on  cardiac  contractions  is  so  obvious  and  necessary 
that  this  gas  has  been  called  the  stimulant  of  the  heart.  It  is  perhaps  more 
accurate  to  say  that  it  is  indispensable  for  the  maintenance  of  its  excitability.  In 
warm-blooded  animals  it  is  the  rapid  exhaustion  of  oxygen  which  causes  the 
heart,  even  when  retaining  its  ganglia,  to  stop  beating  after  a  short  interval 
when  it  is  separated  from  the  animal.  In  dogs  submitted  to  a  pressiire  of  two 
atmospheres,  and  more  in  pure  oxygen,  the  heart  removed  from  the  chest  remains 
longer  in  a  living  condition  (Cj'on),  doubtless  because  the  jirovision  of  vital  gas 
is  gi'eater  in  it.  In  cold-blooded  animals,  in  which  its  consumjDtion  is  less  active, 
contact  with  the  external  air  suffices  to  partially  renew  the  provision  of  oxygen. 
A  frog's  lieart,  emptied  of  blood  and  placed  in  oil,  quickly  stops  beating  (Goltz). 
A  frog's  heart,  in  which  an  artificial  circulation  of  serum  is  kept  up,  will  stop 
beating  when  the  quantity  of  oxygen  contained  in  the  serixm  is  exhausted  ;  it 
will  recommence  beating  if  the  serum  be  changed  ;  if  the  serum  is  coloured  with 
a  little  haemoglobin  which  transports  the  oxygen,  the  heart-beats  will  continue 
persistently  (Kronecker,  Rossbach).  When  the  oxygen  commences  to  give  out, 
the  heart  j^resents  a  special  periodic  rhythm,  which  has  been  studied  by 
Lviciani,  a  rhythm  in  the  coiu"se  of  which  groups  of  pulsations  are  separated 
by  pauses. 

Action  on  the  cardiac  ganglia. — Oxygen  is  necessarj'  for  all  the  tissues  ;  its 
privation  will  cause  muscular  as  also  nervous  paralysis.  But  when  a  heart  is 
asphyxiated,  it  is  its  ganglia  which  first  suffer  from  tliis  privation.  This  will 
be  obvious  from  the  following  experiment.  If,  instead  of  the  entire  heart,  the 
apex  of  the  organ  be  adapted  to  the  carmula  of  an  apparatus  for  keeping  up 
artificial  cumulation,  and  if  its  movements  be  excited  by  electrical  stimulation, 
the  deprivation  of  oxygen  will  no  longer  be  followed  by  the  prompt  and  charac- 
teristic results  which  ensue  when  the  heart  is  beating  automatically  through 
the  action  of  its  ganglia.  It  is  possible,  indeed,  to  cause  blood  charged  with 
carbonic  oxide  to  circulate  in  the  ventricle,  which  is  consequent!}'  deprived  of 
oxygen,  and  nevertheless  the  strength  of  the  beats  will  contmue  dui'ing  a  certain 
time,  which  is  almost  the  same  as  before  (Julia  Divine). 

The  special  mode  of  action  of  oxygen  on  the  cardiac  nerve  tissue  is  not  deter- 
mined. Some  suppose  that  its  role  is  above  all  to  cause  the  disappearance,  by 
oxydizing  them,  of  certain  waste  substances  arising  from  cellular  activity 
(Richet). 

Oxj'gen,  apart  from  the  directly  energetic  action  which  was  attributed  to  it  in 
the  first  instance  by  the  experiments  of  Lavoisier,  thus  possesses  another  in- 
directly energetic,  wliich  may  be  called  an  exciting  action,  or  one  modifying  the 
excitabilit3^  In  both  cases  it  causes  an  expenditiire  of  energy,  but  in  a  very 
different  manner.  In  the  first,  it  follows  a  cycle  of  the  simplest  order  (cycle  of 
chemical  reactions  which  give  off  heat  and  energy)  ;  in  the  second,  it  takes  part 
in  a  cycle  of  the  most  complicated  order  (the  cycle  of  nervous  excitation)  which, 
superadded  to  the  preceding,  plays  in  it  the  part  of  a  power  of  disengagement 
capable  of  attracting  the  reactions  which  themselves  make  use  of  the  greater 
part  of  the  oxygen.  This  current  tlirough  the  organism  of  matter  and  of  energj', 
following  paths  some  direct,  others  more  and  more  roundabout,  is  characteristic 
of  the  living  organization  and  of  its  elaboration 

The  action  of  oxygen  on  the  nerve  centres  is  not,  doubtless,  fundamentally 
different  from  that  wliich  it  exerts  on  the  other  tissues  (the  muscular  for  example). 
But,  as  the  nervous  tissue  has  in  the  animal  organism  a  special  situation  which 
confers  on  it  the  government  of  the  other  tissues,  it  is  obvious  that  this  action 
is  both  more  rapid  and  more  evident. 

X* 


308  SYSTEMATIC    FUNCTIONS 

Action  on  other  centres. — Far  indeed  from  being  special  to  the  gangHa  of  the 
heart,  the  action  of  oxygen  is  exerted  on  the  whole  of  the  nervous  system,  and 
especially  on  the  grey  matter.  According  to  the  organization  of  the  latter,  this 
action  will  have  very  different,  sometimes  even  opposite  effects.  The  oxygen 
which  excites  the  movements  of  the  heart,  by  the  action  which  it  exerts  on  its 
ganglia,  causes  the  cessation  or  slowing  of  those  of  respiration  by  the  opposite 
influence  which  it  possesses  on  the  bulbar  centres  of  the  respiratory  function. 

Thanlis  to  the  oxygen  (to  the  gases  of  the  blood),  the  respiratory  activity  and 
bulbar  excitability  are  so  related  that  one  diminishes  the  other,  and  reciprocally. 
It  is  partly  owing  to  this  compensatory  mechanism  that  the  regulation  of  the 
respiratory  movements  is  effected. 

Action  of  carbonic  acid. — Carbonic  acid  has  an  action  on  the  respiratory  move- 
ments opposed  to  that  of  oxygen,  in  the  sense  that  while  oxygen  provokes  these 
movements  through  its  deficiency,  carbonic  acid  restores  them  by  its  presence. 
On  the  other  hand,  while  a  want  of  oxygen  in  the  blood  favovirs  inspiration,  the 
presence  of  carbonic  acid  in  the  same  fluid  favours  expiration.  A  similar  inver- 
sion of  effect  is  met  with  in  the  cardiac  ganglionic  system  ;  it  is  only  necessary  to 
remember  that  the  effects  of  the  two  gases,  from  the  fact  that  they  are  respectively 
converse,  are  opposite  in  the  heart  to  what  they  are  in  res2:)iration.  It  has  been 
seen  that  the  presence  of  oxygen  is  favourable  to  the  movements  of  the  heart. 
If  this  gas  is  wanting  and  the  heart  is  plunged  inttcs  et  extra  into  an  atmosphere 
of  carbonic  acid,  its  movements  become  slower  and  rapidly  stop.  Is  this  para- 
lysis or  stimulation  ?  It  is  rather  the  latter.  The  heart,  like  the  respiratory 
muscles,  is  submitted  to  two  antagonistic  nervous  influences,  the  one  excito- 
motor,  the  other  moderator  or  inhibitory.  These  influences  are  rejDresented  in 
the  cardiac  ganglia,  as  they  are  lugher  wp  in  the  spinal  cord  and  medulla  ob- 
longata, and  make  use  of  them,  the  first  by  the  cardiac  branches  of  the  great 
syiupathetic,  the  second  by  the  cardiac  branches  of  the  pneumogastric,  both 
having  their  terminations  in  the  ganglia  of  the  heart. 

MeduUo-ganglionic  fibres  of  projection. — The  motor  ganglionic  nuclei  are 
united  to  the  grey  medullary  axis  by  centripetal  and  centrifugal  fibres  which  form, 
above  the  nervous  system  special  to  each  organ,  a  second  system  called  extrinsic 
with  regard  to  this  organ  (although  it  would  be  rather  intrinsic  with  regard  to 
the  nervous  system  itself).  The  analysis  of  a  system  of  this  kind  has  been  sj^eci- 
ally  made  as  concerns  the  heart.  Its  constitution  is  equally  cyclic.  There  are 
fovmd  in  it  :  (o)  centripetal  elements  re]:)resented  by  an  anatomically  distinct 
nerve  in  certain  animals,  the  depressor  nerve,  a  kind  of  very  prolonged  anasto- 
mosis between  the  cervical  cord  of  the  sympathetic  and  the  vagus  (sensitive  to 
the  effects  of  the  intra-cardiac  blood  pressure,  this  nerve  conducts  to  the  medulla 
oblongata  the  impulses  which  this  centre  reflects  on  the  motor  cardio-vascular 
forces,  with  the  object  of  regulating  this  pressure)  ;  (6)  centrifugal  elements, 
which  from  the  medulla  oblongata  and  the  spinal  cord  descend  into  the  ganglia 
of  the  heart  by  the  branches  of  the  vagus  and  of  the  cervico-thoracic  sympa- 
thetic. Of  these  centrifugal  nerves  the  first  are  fnoderator,  that  is  to  say  in- 
hibitory as  regards  the  cardiac  movements  ;  the  others  are  accelerator,  otherwise 
excito-motor  of  these  movements.  Both  differ  profoundly  from  the  nerves  which 
terminate  in  the  muscles,  and  which  for  this  reason  are  called  terminal  nerves. 
It  is  obvious  that  they  act  on  the  intra-cardiac  system,  and  by  it  only,  on  the 
n^iuscles  of  the  heart.  It  is  by  the  intermediation  of  this  system  that  the  first 
moderate  their  action  or  arrest  it,  but  only  for  a  time,  and  that  the  second  accel- 
erate these  muscles,  but  withovit  ever  producing  tetanization.  The  accelerators 
increase  the  nvimber  but  diminish  the  amplitude,  the  moderators  diminish  the 
number  but  increase  the  amplitude  of  the  beats  (Cyon).  Whether  the  intra- 
or  extra-cardiac  system  be  investigated,  a  tendency  to  uniformity  of  the  work 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    309 


of  the  heart  is  observed,  and  this  has  been  confirmed  by  all  authorities  (Marey, 
Dastre,  Gley,  Langendorff). 

The  two  orders  of  fibres  (excito-motor  and  those  of  arrest)  present  a  sort  of 
antagonism  or  mobile  equilibrium  between  themselves,  but  the  intimate  mechan- 
ism by  which  this  is  effected  is  quite  unknown. 


Fig.    128. — Diagram  showing  the  innervation  of  the  heart  in  the  dog. 

gg.ca,  cardiac  ganglia  in  which  the  cardiac  nerves  terminate  ;  gg.ci,  inferior  cervical  ganglion  j 
g  .cs,  superior  cervical  ganglion  ;  gg.pl,  plexiform  ganglion  ;  sym.th,  thoracic  sympathetic  ; 
an.Vi,  ansa  Vieussenii  ;  pn.g,  pneumogastric  ;  n.ve,  vertebral  nerve  ;  Vag.symp,  vago-sym- 
pathetic  ;  sym.c,  cervical  sympathetic  ;  sym.cr,  prolongation  of  the  sympathetic  in  the  skull  ; 
C^,  first  cervical  pair  ;  Di,  first  dorsal  pair  ;  X,  origin  of  the  pneumogastric  ;  XI,  bulbar  origin 
of  the  spinal  accessory  (the  inliibitory  nerves  in  red,  the  motor  nerves  in  blue). 

When  the  activity  of  the  organ  is  no  longer  so  regularly  rhythmical 
the  stimulus  communicated  to  or  maintained  in  it  by  its  ganglia  is 
called  tonic,  and  examples  of  this  form  are  numerous. 

A.  Tonic  Power. — It  is  well  known  what  is  meant  by  tonus,  or  the 


310  SYSTEMATIC    FUNCTIONS 

light  tension  which  is  maintained  in  the  muscles  by  a  permanent 
current  of  weak  excitation  coming  from  the  spinal  cord  so  long  as  it 
remains  in  connexion  with  them,  but  which  ceases  when  this  current 
is  interrupted  by  section  of  the  conducting  nerves.  The  same  thing 
exists  in  the  visceral  muscles,  in  which  the  tonus  is  maintained  as 
much  by  the  spinal  cord  as  by  the  ganglia.  In  order  to  estimate  the 
share  taken  by  these  latter,  all  communication  is  at  first  suppressed 
between  them  and  the  spinal  cord  ;  the  intensity  of  the  motor  pheno- 
mena is  estimated.  The  ganglion  itself  is  removed  ;  once  again  this 
intensity  is  estimated  ;  the  diminution  it  has  undergone  in  each  case 
is  noted.  A  good  method  of  estimating  it  is  to  compare  two  sym- 
metrical regions,  of  which  one  has  been  completely  deprived  of  its 
nerve  supply,  while  the  other  has  preserved  its  ganglionic  apparatus. 

As  evidence  of  this  tonic  activity  of  the  ganglia,  all  phenomena 
depending  on  the  great  sympathetic  may  be  taken  :  calibre  of  the 
vessels,  redness  of  the  cutaneous  or  mucous  surfaces,  dilatation  of  the 
pupil,  condition  of  the  cutaneous  pigmentation,  etc.  Vulpian,  Legros, 
Fr.  Franck,  and  we  ourselves,  have  carried  out  experiments  of  this 
kind,  usually  on  the  ganglia  of  the  cervical  chain  of  the  great  sympa- 
thetic. The  conclusion  arrived  at  is  unanimous  :  the  tonic  poiver  of 
certain  ganglia  is  incontestable,  and  by  parity  of  reasoning  it  cannot  be 
rejected  in  the  case  of  all  similar  ganglionic  masses. 

The  ganglion  has  thus  the  power  of  accumulating  in  itself,  by  hold- 
ing them  in  reserve,  a  certain  number  of  impulses  which  it  has  received 
from  all  the  fibres  which  are  functionally  united  to  it,  which  impulses 
come  to  it  either  from  the  cord  or  from  the  periphery. 

Whether  it  is  a  question  of  a  sphincter  like  the  iris,  or  of  tubes  like 
the  vessels,  or,  further,  of  contractile  cells  like  the  chromatoblasts  of 
the  skin,  the  tonic  influence  of  the  ganglia  cannot  be  doubted.  In 
frogs,  this  tonic  action  is  very  evident.  In  mammals  it  is  very  real. 
It  has  been  clearly  observed  in  the  superior  cervical  ganglion,  the  first 
thoracic  ganglion,  and  the  ophthalmic  ganglion  so  far  as  concerns  the 
iris  (Liegeois,  Vulpian,  Tuwim,  Fr.  Franck).  It  has  been  demon- 
strated in  these  same  ganglia  (except  the  ophthalmic)  so  far  as  concerns 
the  vessels  of  the  tongue  (Vulpian),  in  the  superior  cervical  ganghon 
as  regards  the  vessels  of  the  ear  (Morat).  These  examples  sufficiently 
prove  that  this  tonic  action  is  general,  and  that  this  would  be  estab- 
lished if  it  were  sought  for  in  other  motor  nuclei  of  the  great  sym- 
pathetic and  the  equivalent  nerves. 

Concerning  the  origin  and  the  point  of  departure  of  this  stimulus 
here  made  manifest  in  a  sustained  manner,  and  for  a  longer  or  shorter 
period  after  the  isolation  of  the  ganglia  from  their  medullary  connexions, 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    311 

the  same  remark  applies  that  has  been  made  above,  this  point  of  depar- 
ture probably  consisting  partially  in  a  reflex  impulse  transmitted  by 
centripetal  nerves  which  are  as  yet  indistinct. 

B.  Reflex  Power. — CI.  Bernard  was  the  first  to  suspect  and  to 
demonstrate  experimentally  the  possibility  of  the  occurrence  of  gangli- 
onic reflex  actions.  He  operated  on  the  sub-maxillary  ganglion.  He 
cut  the  lingual  nerve  above  its  sub-maxillary  branch  (which  passes 
through  the  ganglion  of  the  same  name)  in  such  a  way  as  to  completely 
separate  the  superior  centres  from  the  subjacent  system.  By  stimu- 
lating (electrically,  not  by  the  use  of  sapid  substances)  the  tip  of  the 
tongue,  he  observed  saliva  issuing  from  Warton's  duct.  A  reflex 
circuit  was  thus  established  between  the  tip  of  the  tongue  and  the 
gland  by  the  intermediation  of  the  ganglion. 

Schift"  has  contested  the  accuracy  of  this  experiment  ;  but  Wert- 
heimer,  who  has  repeated  it,  criticizes  Schiff's  objections  and  rejects 
them.  Langley  observes  that  the  ganglion  which,  in  the  dog,  is  called 
sub-maxillar}^  is  in  reality  the  ganglion  of  the  sub-lingual ;  the  real 
sub-maxillary  ganglion  is  made  up  of  a  mass  of  cells  situated  in  the 
hilum  of  the  gland  of  the  same  name.  This  anatomical  detail,  although 
displacing  the  centre  of  reflexion  from  one  ganglionic  mass  to  another, 
in  no  degree  invalidates  the  conclusion  of  CI.  Bernard. 

This  experiment  has  since  been  repeated  by  several  observers  and 
applied  by  them  to  other  ganglia,  either  of  the  chain  or  of  the  branches 
of  the  sympathetic. 

C.  Inhibitory  Power. — In  the  exact  sense  which  we  attribute  to 
this  word,  inhibition  is  the  arrest  of  the  movement  about  to  take  place, 
an  arrest  caused  by  an  activity  conflicting  with  tliat  which  originates 
this  movement.  For  the  stimulus  which  is  projected  into  a  nerve  to 
have  an  effect  so  diametrically  opposed  to  that  which  is  recognized  in 
it  as  logical  and  natural,  it  is  necessary  that  on  some  part  of  the  course 
it  follows  it  should  undergo  a  transformation  of  a  more  or  less  radical 
kind,  b}^  which  its  effect  is  changed.  The  ganglia  of  the  great  sympa- 
thetic form  a  locality  of  this  kind.  This  has  been  demonstrated  by 
Dastre  and  myself,  by  a  characteristic  experiment  performed  on  the 
dorsal-cervical  sympathetic  of  the  rabbit. 

Demonstration. — The  stimulation  applied  to  the  cervical  chain  heloiv 
the  ganglia  of  the  base  of  the  neck  causes  contraction  to  such  an  extent 
as  to  obhterate  the  vessels  of  the  rabbit's  ear  (CI.  Bernard,  Brown- 
Sequard).  A  stimulus  applied  above  these  ganglia,  to  the  thoracic 
chain  in  its  superior  portion,  causes  an  enormous  dilatation  of  these 
same  vessels, that  is  to  say,  inhibits  the  vascular  tonus  (Dastre  and  Morat). 
A  similar,  but  less  constant,  effect  is  observed  by  stimulating  com- 


312  SYSTEMATIC    FUNCTIONS 

paratively  the  lumbar  chain  above  and  below  its  first  ganglia.  These 
are  the  earliest  experiments  by  which  the  phenomena  of  inhibition 
have  been  accurately  localized. 

Inhibition  in  the  Invertebrata. — In  the  cephalopoda  Physalix  has  observed 
the  following  facts.  The  pigmentary  sj^ots,  the  chromatophores,  by  their  en- 
largement or  contraction  change  the  colour  of  the  animal.  The  enlargement 
produces  darkening  of  the  skin  by  the  spreading  out  of  the  patches  ;  it  is  caused 
by  the  radiating  mviscles  arranged  round  the  clii'omatophore.  The  contraction 
of  the  cliromatophores  produces  pallor  ;  it  is  due  to  an  elastic  power  opposed 
to  the  preceding.  Stimulation  of  the  pallial  nerve  causes  the  chromatophores 
to  dilate  by  contraction  of  the  radiating  muscles  (the  skin  darkens  in  conse- 
quence). Its  section  produces  the  opposite  effect.  The  pallial  nerve  arises  in 
the  sub-oesoi^hageal  ganglia,  which  are  thus  centres  for  the  chromatophores. 
Above  the  latter  are  the  cerebroid  ganglia.  But  these  latter  ganglia  may  exercise 
an  inhibitory  suspensive  action  over  the  first  of  svich  a  nature  that  a  stimulus, 
starting  from  these  ganglia  (directly  or  reflexly),  causes  pallor  of  the  skin  (by  a 
cessation  or  loss  of  contraction  of  the  radiating  muscles  of  the  chromatophores). 
When  the  cerebroid  ganglia  are  separated  from  the  sub- oesophageal  ganglia  by 
a  section,  this  inhibitory  phenomenon  becomes  impossible  ;  stimuli,  whether 
direct  or  reflex,  uniformly  produce  darkening  of  the  skin.  Here  again  inhibition 
l^resents  itself  as  a  conflict  or  a  transformation  of  the  impulses  effected  in  a  ganglion, 
and  consequently  in  tlie  interior  of  the  nervous  system. 

Various  forms  and  aspects  of  the  transformation  of  the  Impulse. — The  reflex 
power,  the  tonic  power  and  the  inhibitory  power  of  the  ganglia  of  the  gi'eat 
sympathetic  are  not  in  reality  three  distinct  things,  but  three  difl'erent  aspects 
of  the  very  general  function  of  transformation  of  impulses  which  is  delegated  to 
them,  and  this  function  is  an  essential  attribute  of  the  grey  nervous  matter. 
The  ganglia  of  the  great  sympathetic  are  neither  more  nor  less  than  character- 
istic jjortions  of  this  matter,  disseminated  through  the  organs  instead  of  being 
condensed  in  a  hollow  region,  but  nevertheless  connected  with  other  divisions 
of  this  substance,  as  well  as  amongst  themselves,  by  links  analogous  to  the  white 
tracts  in  the  nervous  centres. 

1.  System  of  the  life  of  relation  ;  System  of  the  vegetative  life  : 
Resemblances  and  differences. — The  two  systems,  the  one  known  as 
the  life  of  relation,  the  other  as  the  vegetative  life,  in  spite  of  their  pro- 
found external  difference,  are  constructed  on  the  same  fundamental 
type  which,  for  the  sake  of  clearness,  it  will  be  necessary  once  again  to 
recapitulate.  They  are  both  composed  of  reflex  arcs  or  superposed 
nervous  circuits.  These  circuits  differ  as  regards  their  situation  and 
their  relative  importance,  their  connexion  with  unlike  organs,  and  the 
very  unequal  development  in  them  of  psychical  phenomena  which  are 
based  on  sensation. 

The  first  has  very  elongated  inferior  arches,  so  long  indeed  that  they 
enter  by  their  apex  into  the  cerebro-spinal  cavity.  On  these  inferior 
arches  a  highly  developed  and  complicated  superstructure  is  based, 
which  expands  itself  in  the  upper  part  of  this  cavity.  It  is  this  which 
has  caused  the  system  to  be  known  by  the  somewhat  unsatisfactory 


CONSCIOUS    AND  UNCONSCIOUS  :    THEIR  SEPARATION  313 

name  of  cerebro-spinal.  The  second  has  its  much  shorter  inferior 
arches,  all  situated  outside  the  vertebral  canal  and  disseminated  in 
the  organism  in  more  or  less  immediate  contact  with  the  apparatus 
which  it  encloses  like  a  net :  whence  has  arisen  the  notion  of  the  older 
observers  that  it  is  the  bond  of  union  between  their  functional  sym- 
pathies ;  this  conception  is  not  absolutely  false,  but  it  no  more  defines 
this  system  than  the  denomination  of  cerebro-spinal  defines  the  pre- 
ceding one.  On  these  extra-rachidian  arches  a  superstructure  is  also 
built  up  which  is  infinitely  less  developed  and  much  less  apparent  than 
the  preceding  one,  in  which  it  proceeds  to  immerse  itself  in  the  region 
of  the  spinal  cord,  not  without  communicating  with  the  brain,  but 
without  it  being  possible  in  this  latter  to  make  any  categorical  distinc- 
tion between  the  one  and  the  other  system.  Further,  this  distinction, 
which  is  so  obvious  in  the  peripheral  regions,  where  the  nerves  come 
in  contact  with  differentiated  organs,  must  necessarily  be  less  so  in  the 
deeper  regions,  where  all  the  conducting  paths  converge  in  order  to 
effect  the  unity  of  the  living  organism. 

2.  Mechanical  and  chemical  acts  ;  Contraction,  Secretion. — The 
connexions  of  the  great  sympathetic  with  the  component  apparatus 
of  the  organism  are  numerous,  varied  and  graduated,  and  new  ones 
are  daily  being  discovered.  While,  in  fact,  the  relations  of  the  organism 
with  the  exterior  are  effected  by  a  single  category  of  organs,  the  striated 
muscles,  and  by  a  single  miodality  of  movement,  the  contraction  of 
these  muscles,  nutrition  and  the  involuntary  life  of  the  organs  which 
take  part  in  it  require  a  fairly  large  number  of  cellular  acts  dilTering 
greatly  the  one  from  the  other  as  regards  their  intimate  detail.  Never- 
theless, they  may  be  reduced  to  two  principal  categories  which  are 
perceptible,  some  under  a  predominently  mechanical  aspect,  which  is 
essentially  muscular  contractioii  ;  others  under  an  aspect  which  is 
rather  chemical,  and  which  brings  about  what  we  know  as  glandular 
secretion,  or  the  elaboration  of  special  products  by  mutual  reaction  of 
the  component  elements  of  the  protoplasm. 

Connexion  of  the  two  phenomena. — These  acts  are  not  as  completely 
independent  as  might  be  imagined  from  these  designations,  because 
both  the  one  and  the  other  have  for  their  first  point  of  departure  the 
molecular  phenomena  and  the  expenditure  of  energy  excited  by  the 
nervous  system  in  the  protoplasm  of  the  cells.  Both  manifest  them- 
selves finally  by  a  displacement  of  substances,  rendered  visible  by  the 
flow  of  liquid  which  proceeds  from  certain  glands,  or,  more  obscurely, 
by  the  exchanges  which  every  cell  maintains  with  the  blood. 

Every  organ  indeed,  if  it  be  muscular,  has  an  internal  secretion, 
every  gland  produces   a  movement  of  liquid.     Further,   the  glands 


314  SYSTEMATIC    FUNCTIONS 

present  a  great  variety  of  elements,  comprising  amongst  them  veritable 
muscular  cells.  And  the  contractile  elements,  also,  which  are  under 
the  control  of  the  great  sympathetic,  present  a  variety  and  a  gradua- 
tion which  are  extremely  marked,  from  the  striated  fibres  of  the  heart 
muscle  to  the  pigmentary  cells,  and  even  to  the  fixed  cells  of  the  con- 
nective tissue,  which  some  observers  suppose,  and  not  without  reason, 
to  be  influenced  by  the  ganglionic  nervous  system.  Between  these 
extremes  a  transitional  form  is  represented  by  the  non-transversely- 
striated  muscular  element  (fibre  cells,  smooth  muscles),  which  is  not 
special  to  organic  life,  since  in  many  of  the  invertebrata  these  elements 
are  the  only  ones  which  carry  out  the  commands  of  the  will. 

3.  Specific  stimulation  of  the  sensory  nerves  of  the  deeply  situated 
Organs. — There  is  no  doubt  that  the  centripetal  elements  of  the  great 
sympathetic  receive  their  excitation  from  special  apj^aratus  analogous 
to  those  of  the  superior  senses  and  distributed  either  to  the  surfaces 
of  the  large  cavities  or  in  the  depth  of  the  organs.  Up  till  the  present 
time  we  are  poor  in  anatomical  data  concerning  this  point. 

Anatomical  data. — Dogiel,  who  has  made  a  very  complete  study  of  the  ele- 
ments of  the  great  s^'mpathetic,  describes  a  variety  of  these  elements  whose  very 
long  dendrites  proceed  from  the  ganglion  in  which  their  cell  is  contained,  become 
involved  in  a  small  nerve  trunk  and  then  place  themselves  in  contact  with  the 
epithelial  surface.  These  dendrites  were  at  first  regarded  as  axons  ;  they  are 
distinguished  from  the  latter  by  their  dichomotic  division  and  by  the  absence 
of  collaterals  ;  they  have  some  analogy  with  the  eellulipetal  prolongation  of 
the  sensory  nerve  of  a  spinal  ganglion  ;  in  fact,  at  a  certain  distance  from  the 
cell  these  long  dendritic  prolongations  are  obser\-ed  to  be  covered  with  myelin. 

Such  elements  have  been  met  with  in  the  heart,  under  the  pericardial  serous 
membrane  ;  in  the  intestine,  where  their  ramifications  unite  the  mucous  inem- 
brane  with  the  plexiform  ganglion  of  Auerl^ach. 

4.  Experimental  data. — Popielski,  Wertheimer  and  Lepage  have 
performed  experiments  concerning  the  pancreatic  secretion  which 
demonstrate  ah  origine  ad  terminum  a  functional  cycle  of  unconscious 
vegetative  life,  as  also  the  more  or  less  marked  developments  which 
this  cycle  may  undergo  in  the  interior  of  the  nervous  system.  It  starts 
in  a  specific  stimulus  and  it  terminates  in  a  specific  act,  passing  through 
nervous  paths  which  experiment  localizes  at  its  will  in  systems  whose 
dimensions  and  complexity  differ. 

Relation  between  the  nature  of  the  Stimulus  and  the  work  produced. 
— The  injection  of  an  acid  solution  (HCl.  5  ])er  100)  into  the  duodenum 
excites  the  secretion  of  pancreatic  juice,  which  may  be  observed  appear- 
ing at  the  extremity  of  a  cannula  placed  in  the  duct  of  the  gland.  In 
the  normal  condition  it  is  the  chyme  impregnated  with  the  acid  of  the 
gastric  juice  which  provokes  this  phenomenon  of  secretion,  and  among 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    315 

the  properties  of  the  'pancreatic  juice  its  alkalinity  must  be  included, 
which  neutrahzes  the  acidity  of  the  gastric  secretion  passing  into  the 
intestine.  Other  stimuU  like  ether  (CI.  Bernard)  or  chloral  (Wert- 
heimer  and  Lepage)  can  provoke  the  reflex  secretion,  but  in  the  way  of 
general  stimulation  ;  while  the  acid  seems  here  to  be  a  specific  stimulus 
appropriate  to  the  function  (or  to  which  the  function  is  appropriated). 

Not  only  in  the  duodenum,  but  also  at  a  certain  distance  from  the 
latter,  in  the  superior  third  of  the  small  intestine,  the  acid  stimulation 
has  the  same  effect.  Below  this  point  it  is  without  action,  either 
because  the  appropriate  nerve  terminations  are  wanting,  or  because 
the  nervous  paths  of  association  are,  from  this  point  of  view,  lacking 
between  the  lower  intestine  and  the  pancreas. 

Variable  extension  of  the  cycle. — It  may  be  proved  that  the  reflec- 
tion occurs  in  a  system  which  is  sometimes  purely  local  (hmited  to  the 
intestinal  organs),  sometimes  comprises  the  abdominal  ganglia,  and 
sometimes  includes,  further,  the  spinal  cord  and  the  nerve  masses 
which  overlie  it. 

(a)  Local  Reflex. — Wlien  the  coeliac  and  mesenteric  ganglia  (even  the  spinal 
cord)  liave  been  removed,  the  acid  stimulation  of  the  duodenal  mucous  membrane 
provokes  pancreatic  seci'etion,  evidently'  through  a  nervous  path,  by  a  reflection 
of  the  stiniuhis  on  the  special  ganrflia  ichich  anatomy  proves  to  he  present  in  the 
pancreas. 

This  experiment  is  allied  to  that  wliich  is  made  on  the  ganglia  of  the  isolated 
heart,  but  it  is  more  convincing,  in  the  sense  that  the  operator  is  here  master  of 
the  stimulus  and  that,  instead  of  an  autoinatic  undecomposable  phenomenon, 
an  obvious  reflex  act  is  in  question. 

(b)  Ganglionic  Reflex. — ^Mien  the  cord  is  removed  and  the  ccBliac  and  mesen- 
teric ganglia  are  preserved,  the  same  reflex  effect  is  possible  ;  but  the  participa- 
tion of  the  ganglia  referred  to  above  can  be  demonstrated  in  it.  If,  indeed,  the 
duodenum  be  separated  from  the  small  intestine  by  a  strong  ligature,  stimulation 
of  the  small  intestine  (by  injection  of  an  acid  solution)  provokes  the  pancreatic 
secretion.  The  propagation  of  this  excitation  can  no  longer  be  local  as  in  the 
preceding  case,  but  requires  the  intervention  of  the  abdominal  ganglia  (or  even 
of  the  sympathetic  chain)  as  the  path  of  association  of  the  two  separated  segments 
of  the  intestine  and  of  the  reflection  of  one  on  the  other. 

(c)  Spinal  Reflex. — Wlien  the  cord  is  intact  and  its  connexions  -ndth  the  intestine 
and  the  pancreas  are  maintained,  there  is  no  doubt  that  it  maj^  serve  as  the  site 
of  reflection  for  the  impulses  propagated  from  the  one  to  the  other.  Not  only 
the  cord,  but  the  bulb  and  the  brain  may  take  part  in  the  regulation  of  acts  of 
this  order,  although  they  are  involuntary  and  vmconsciovis. 

5.  Mixture  of  stimulating  and  inhibitory  influences. — The  system 
which  reflects  and  co-ordinates  these  impulses  is  certainly  complex, 
even  when  it  is  experimentally  reduced  to  its  smallest  dimensions 
Like  every  other  of  the  same  class,  it  employs  elements  some  of  which 
transmit  the  impulse,  while  others  inhibit  it.  It  is  remarkable  that  the 
force  (and  probably  the  number)  of  these  latter  progressively  increases. 


316  SYSTEMATIC    FUNCTIONS 

in  proportion  as  the  system  becomes  more  complicated,  in  arriving  at 
the  abdominal  ganglia  and  especially  the  spinal  cord. 

So-called  paralytic  secretion. — The  most  abundant  secretion  is  not 
that  which  takes  place  with  the  concurrence  of  the  cord,  but  is  on  the 
contrary  that  which  the  purely  local  cycle  puts  in  action  (Wertheimer 
and  Lepage).  The  removal  of  the  abdominal  ganglia  may  suffice  to 
cause  a  flow  of  pancreatic  juice  (CI.  Bernard)  :  this  is  known  as  para- 
lytic secretion,  it  being  regarded  as  a  consequence  of  the  dilatation  of 
the  vessels  of  the  gland.  It  may  with  more  plausibility  be  attributed 
to  the  suppression  of  controlling  actions  appertaining  to  the  spinal 
cord. 

The  study  of  the  functions  of  vegetative  life  demonstrates  or  leads  to  the  sus- 
picion that  there  are  many  exainples  of  the  same  kind,  in  which  it  is  necessary 
to  allow  that  chemical  or  mechanical  stimuli,  tlirough  the  intermediation  of 
given  nervous  cycles,  regulate  nutrition  or  the  movement  of  the  parts.  The 
larger  number  of  the  hollow  muscles  proportion  their  contractions  to  their  state 
of  repletion  and,  hence,  of  their  tension  or  distension.  The  contractions  of  the 
heart  are  regulated  by  the  condition  of  the  blood  pressure,  with  the  aim  in  view 
of  maintaining  in  a  constant  condition,  by  the  intermediation  of  its  sensory 
nerve,  the  deqnessor  nerve.  The  composition  of  the  blood  is  itself  regulated  by 
the  stimulations  arising  from  its  aberrations  by  a  mechanism  of  wliich  the 
pancreatic  secretion  affords  an  example  at  the  very  entrance  of  the  paths  of 
absorption. 

3.     Special  Functions  of  the  Great  Sympathetic 

The  great  sympathetic  can  be  resolved  into  a  certain  number  of 
systems  which  are  fairly  exactly  superposable  (motor,  secretory,  each 
one  subdivisible  into  different  varieties  :  vaso-motor,  sudoriparous, 
etc.,  etc.),  in  which  the  mixture  of  their  fibres  has  often  led  to  a  con- 
fusion being  made  between  them,  but  of  which  it  is  possible  to  demon- 
strate the  independent  reality.  Physiology  has  different  means  not 
only  of  bringing  them  into  action,  but  also  of  dissociating  them,  thanks 
to  their  elective  affinities  for  certain  poisons.  Example  :  stimulation 
of  the  cutaneous  nerves  simultaneously  modifies  the  circulation  of  the 
skin  and  the  secretion  of  its  glands.  It  may  be  asked  if  the  secretion 
is  not  merely  the  consequence  of  the  circulatory  change  (vaso-dilata- 
tion).  But,  if  a  weak  dose  of  atropine  (1  milligramme)  be  injected 
into  the  blood  of  an  animal,  stimulation  of  cutaneous  nerves  causes 
the  same  circulatory  effects,  but  no  longer  excites  secretion  of  the 
glands.  Therefore  the  poison  has  paralysed  the  glandular  nerves 
separately  ;  hence  the  latter  exist  independently  of  the  vaso-motor 
nerves.  These  different  functions  have  been  successively  discovered, 
and  we  cannot  flatter  ourselves  that  we  know  them  all.  It  is  probable 
that  the  great  sympathetic   presides   over  a  large   number   of  fixed 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    317 

elements  of  the  tissues,  whose  relations  with  the  nervous  system  are 
not  at  the  present  time  accurately  known. 

Historical. — It  is  in  operating  on  the  cervical  portion  of  the  great 
sympathetic,  which  is  more  accessible,  that  the  principal  discoveries 
concerning  its  functions  have  been  made. 

Initial  fact  ;  Orientation  of  the  conduction. — The  earliest  is  that  of 
Petit  (of  Namur)  known  as  Pourfour  Dupetit,  who  observed,  as  a  con- 
sequence of  section  of  the  cervical  sympathetic,  those  phenomena  which 
are  known  as  oculo-pupillary  (sinking  of  the  globe  of  the  eye,  contrac- 
tion of  the  pupil)  ;  these  phenomena  are  explicable,  the  first  by  the 
loss  of  tone  of  the  inhibitory  elements  of  the  sphincter  muscle  of  the 
iris,  the  second  by  the  loss  of  tone  of  the  muscular  elements  of  the 
capsule  of  Tenon.  This  double  mechanism  was  not  only  unknown, 
but  was  incomprehensible  to  the  originator  of  this  experiment,  who 
observed  the  change  in  the  aspect  of  the  eye  as  a  whole,  but  without 
inquiring  into  its  mechanism.  But  by  this  observation  he  established 
a  fact  new  and  important  for  that  epoch,  namely  that,  contrary  to  the 
other  motor  nerves  which  ajtpear  to  descend  from  the  brain,  this  latter 
ascends  in  starting  from  the  simial  cord  toicards  the  head  ;  this  was  to 
distinguish,  by  one  of  its  most  striking  characters,  the  systematization 
of  the  great  sympathetic  as  regards  that  of  the  other  nerves. 

Bifii  in  1841  performed  the  counter  experiment,  consisting  in 
stimulating  the  superior  end  of  the  cut  nerve,  which  induces  dilatation 
of  the  pupil  and  exophthalmos. 

Vaso-motor  function. — CI.  Bernard  (1851)  performed  on  this  same 
nerve  an  experiment  which  is  still  regarded  as  classical.  Having  cut 
the  symjMthetic  in  the  neck  of  a  rabbit,  he  observed  that  the  temperature 
of  the  ivhole  of  the  corresponding  side  of  the  head,  es])ecially  of  the  ear, 
was  remarkably  raised.  On  making  the  counter  experiment  by  stimu- 
lating the  superior  end,  he  observed  that  the  temperature  fell  beloiv  the 
original  temperature,  as  Brown-Sequard  had  observed  almost  contem- 
poraneously* 

The  announcement  of  this  fact  caused  much  astonishment.  Of 
relationship  between  the  temperature  and  nerve  action,  between  a  fact 
markedly  physical  on  the  one  hand  and  a  fact  just  as  markedly  vital 
on  the  other,  none  was  clearly  seen.  Brown-Sequard  and  Waller 
called  attention  to  the  fact  that  this  relationship  was  not  direct.  Sec- 
tion of  the  sympathetic  paralyses  the  muscles  of  the  vessels  which  are 
located  in  the  field  of  distribution  of  the  great  sympathetic,  and  its 
stimulation  causes  them  to  contract.  This  nerve  is  not  thermic  in 
function,  but  vaso-motor  ;  it  diverts  the  distribution  of  the  blood  from 
the  deep  structures  to  the  periphery  and  thfis  transports  the  heat  from 


318 


SYSTEMATIC    FUNCTIONS 


the  warm  regions  to  those  which  are  cooler.     Such  is  the  real  explana- 
tion of  the  experiment  of  CI.  Bernard. 

It  has  an  extreme  importance,  because  it  reveals  both  the  unsus- 


FiG.   129. — Effects  of  the  stimulation  of  the  cervical  sympathetic  in  the  dog. 

The  excitation  is  directed  to  the  cephalic  end  of  tlie  common  trunk  of  the  vagus  and  of  the 
sympathetic  in  tlie  neck.  The  vagus  has  been  previously  cut  at  tlie  base  of  the  skull  in  order 
to  ehminate  the  reflex  effects  to  wliich  it  may  give  rise.  Stimulation  can  also  be  brouglit  to  bear 
on  the  sympathetic  at  the  point  where  it  is  separated  from  the  vagus,  either  below  the  superior 
cervical  ganglion,  or  at  the  level  of  the  ansa  Vieussenii. 

Oculo-pupillary  effects  consisting  in  dilation  of  the  pupil  and  projection  of  the  eyeball. 

Vaso-motor  effects  consisting  in  pallor  of  the  tongue  and  ear  on  the  side  corresponding  to  the 
excitation  (constrictive  effect)  and  redness  of  the  hps,  the  gums  and  the  palatine  arch  on  the 
same  side  (dilatory  effect  or  one  tlie  result  of  inhibition  of  the  vascular  contraction).  .Jonesco 
and  Floresco  have  confirmed  this  double  vaso-motor  effect  in  man. 

pected,  or  very  vaguely  suspected,  existence  of  vaso-motor  nerves  and 
also  their  localization  in  the  great  sympathetic. 

Double  Motor  and  Inhibitory  Function. — Dastre  and  Morat  in  1881 
showed  that  stimulation  of  the  great  cervical  sympathetic,  in  addition 
to  the  oculo-pupillary  effects  described  above,  and  of  the  constriction 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION     319 

of  the  vessels  of  localities  which  are  habitually  obvious  like  the  ear, 
causes  the  dilatation  of  those  of  neighbouring  regions,  the  npper  and  lower 
lip,  the  palatine  arch,  and  this  very  clearly  in  the  dog.  Hence  the  sym- 
pathetic contains  inhibitory  vascidar  nerves. 

CI.  Bernard  had  previously  shown  (1858)  by  stimulation  of  the  chorda 
tympani,  the  existence  of  nerves  possessing  the  function  of  dilating  the 
vessels.  For  this  very  reason  the  reality  of  the  vaso-dilatory  action  of 
the  great  sympathetic  was  disputed,  it  being  considered  that  the  same 
nerve  could  not  unite  in  itself  two  such  opposite  functions.  But  this 
functional  antagonism  between  nerve  elements  belonging  to  the  same 
group,  is  that  which  gives  the  chief  interest  to  this  experiment.  On 
this  account  the  great  sympathetic  ceases  to  be  a  nerve  like  the  others,  and 
becomes  in  reality  a  systematized  assemblage. 

Not  merely,  indeed,  does  it  contain  similar  elements  governing  the 
circulation  of  neighbouring  regions,  but  these  elements  are  seen 
arising  from  different  points  of  the  spinal  cord,  converging  the  one 
towards  the  other,  and  in  certain  cases  it  is  possible  to  point  out 
the  spot  in  which  they  influence  one  another. 

Localization  of  inhibition  in  the  ganglia. — We  have  called  attention 
above  to  the  manner  in  which  the  vascular  results  of  stimulation  change 
their  character  according  as  this  stimulation  is  applied  above  or  below 
certain  ganglia  of  the  chain  (inferior  cervical  and  first  thoracic)  situated 
on  its  course  ;  how  that  which  is  made  below  has  purely  constrictive 
effects,  while  that  made  above  is  followed  generally  by  those  of  dilata- 
tion, which  in  certain  cases  are  intermingled  with  constrictive  effects. 
By  investigating  separately  some  of  the  spinal  origins  of  the  cervical 
great  sympathetic,  others  may  be  found  of  which  some  cause  dilatation 
and  others  contraction  of  the  vessels  of  the  locality  in  question.  From 
this  it  must  be  concluded  that  the  motor  nuclei  of  the  vessels  of  the 
ear  are  situated  in  these  ganglia,  and  that  the  branches  which  the  latter 
receive  from  the  thoracic  spinal  cord  are  fibres  of  projection,  some 
excito-motor^  others  inhibitory.  The  stimulation  passes  from  a 
superior  to  an  inferior  cycle,  as  when  it  is  transmitted  from  the  cerebral 
cortex  to  the  spinal  cord  when  the  skeletal  muscles  are  in  question. 

Secretory  function. — In  1880  Luchsinger  observed  that  stimulation 
of  the  cervical  cord  causes  an  abundant  secretion  of  the  sudoriparous 
glands  in  certain  regions  of  the  face  (groin  in  the  pig,  muzzle  in  the  ox), 
just  as  that  of  the  dorso-lumbar  sympathetic  causes  secretion  of  the 
glands  of  the  hind-limb  in  the  cat  and  dog.  Czermak  had  already 
observed  that  stimulation  of  the  cervical  cord  reacts  on  the  sub- 
maxillary gland,  causing  a  very  thick  saliva  to  flow  from  it  ;  in  both 
cases  the  motor  or  secretory  nerves  of  the  glands  are  put  in  action,  this 


320  SYSTEMATIC    FUNCTIONS 

being  another  species  of  nervous  action  which  may  be  added  to  the 
preceding. 

CI.  Bernard,  in  investigating  the  effects  of  the  section  of  the  cervical 
cord  in  the  horse,  had  observed  that  the  corresponding  side  of  the  face 
and  neck  was  covered  with  sweat.  But  this  phenomenon  was  then 
interpreted  as  being  dependent  on  the  vascular  paralysis  which  follows 
this  section.  It  is  probable  that  it  means  something  further,  namely, 
the  cessation  of  an  inhibitory  influence  conveyed  by  the  great  sym- 
pathetic to  the  sweat  glands. 

Inhibito-secretory  function. — Arloing  (1890-1891),  having  cut  this 
nerve  in  the  neck  in  the  ass,  observed  after  some  days  that  the  sebaceous 
glands  of  the  external  ear  ivere  cramfned  ivith  their  secretion,  and  he  re- 
garded this  result  as  being  one  of  the  first  observations  concerning  the 
inhibitory  action  of  the  sympathetic  on  the  glands.  This  author  points 
out  facts  of  the  same  nature  relating  to  the  lacJiryrnal  gland  and  to  the 
Meibomian  glands. 

Function  of  accommodation  for  distant  vision. — Morat  and  Doyon 
(1891)  observed  that  stimulation  of  the  same  nerve  produced  not  only 
dilatation  of  the  pupil,  but  a  contemporaneous  flattening  of  the  crystalline 
lens,  which  they  recognized  by  the  enlargement  of  the  crystalline  image 
(second  image  of  Purkinje)  at  the  instant  of  stimulation.  From  this 
they  concluded  that  the  symjjathetic  governs  acco^mnodation  for  distant 
vision. 

Vaso-motor  lymphatic  function. — P.  Bert  and  Laffont,  by  stimulat- 
ing the  mesenteric  nerves,  caused  a  contraction  of  the  chyliferous 
vessels.  Gley  and  Camus,  operating  on  the  thoracic  sympathetic  or 
splanchnic  nerve,  obtained  variations  of  calibre  of  the  thoracic  duct 
and  of  the  cistern  of  Pecquet  (receptaculum  chyli),  generally,  rather 
in  the  direction  of  inhibition,  but  also  in  that  of  constriction. 

Pilo-motor  function. — Stimulation  of  the  sympathetic,  especially  in 
the  trunk,  causes  the  hair  to  stand  on  end  in  the  corresponding  cutaneous 
area.  This  effect,  vaguely  recognized  by  other  experimenters,  was 
observed  for  the  first  time  in  satisfactory  conditions  and  described  in 
detail  by  Langley,  who  has  thus  determined  the  pilo-motor  function  of 
the  great  sympathetic  (1S91). 

Glyco-formative  function. — By  stimulating  the  great  splanchnic 
nerve  Morat  and  Dufourt  caused  an  increased  activity  of  sugar  forma- 
tion in  the  liver  at  the  expense  of  the  glycogen  of  this  organ,  and  they 
observed  that  this  effect  is  not  directly  subordinated  to  the  hepatic 
circulation,  which  proves  the  existence  of  distinct  nerves  controlling 
the  intra-cellular  chemistry  of  the  gland.  This  is  an  example  of  an 
internal  secretion  controlled  by  the  nervous  system. 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    321 

Chromatic  function. — P.  Bert,  experimenting  on  the  chameleon, 
noticed  the  influence  of  the  great  sympathetic  on  the  changes  of  colour 
of  the  skin,  an  influence  which  is  equally  observable  in  the  frog  after 
the  removal  of  the  ganglia  of  the  great  sympathetic  (especially  the 
superior  cervical  ganglion),  as  Vulpian  has  demonstrated. 

Thus  it  is  seen  that  the  great  sjaiipathetic  represents,  as  regards  motricity, 
very  different  fvmctions.  While  the  voluntary  nerves  preside  only  over  the 
striated  muscles  of  the  skeleton,  the  sympathetic  has  under  its  control  a  species 
of  cells,  varied  and  graduated  both  in  form  and  function,  which  range  from  the 
muscular  striated  fibres  of  the  heart  to  the  glyco-formative  cells  of  the  liver, 
passing  through  the  smooth  muscles  of  the  intestine  and  the  vessels,  and  the 
contractile  and  secreting  epithelia  of  the  most  diverse  form  and  nature.  While 
the  voluntary  system  carries  out  these  motor  combinations  (fundamentally  also 
very  numerous)  by  the  aid  of  a  single  element,  the  muscular  fibre,  the  invokm- 
tary  system  discharges  its  fmictions  by  the  help  of  extremely  differentiated 
elements.  In  the  division  which  the  two  systems  have  effected  of  the  com- 
ponent elements  of  tlie  organism,  the  one  has  taken  a  portion  of  the  muscvxlar 
tissue,  the  other  the  remainder  of  the  elements  ;  whence  the  extreme  importance 
of  this  latter  in  the  primitive  functions  of  the  living  being,  and  on  this  account 
indeed  in  the  pathological  study  of  these  functions. 

Methods  of  determination. — In  order  to  distinguish  these  divers  activities 
from  each  other  and  to  discriminate  at  the  same  time  between  the  nerve  elements 
which  correspond  to  them,  recourse  is  had  to  methods  which  vary  according  to 
the  circumstances.  Examj^les  :  the  contraction  and  dilatation  of  the  jDupil  are 
directly  observable,  as  also  the  erection  of  the  hair  ;  the  contraction  and  dilata- 
tion of  the  vessels  can  equally  be  appreciated  de  visu,  when  an  isolated  artery  is 
observed,  such  as  the  auricular  artery  of  the  rabbit.  The  condition  of  the  capil- 
lary circulation  in  a  superficial  area  (skin,  mucous  membrane)  may  be  ascertained 
by  the  changes  of  colour  of  this  locality,  which  becomes  paler  or  redder  according 
to  the  quantity  of  blood  circulating  in  it  {colouriscopic  tnethod).  A  less  direct 
method,  but  one  which  is  very  accurate,  consists  in  estimating  and  recording  the 
'pressure  or  the  rate  of  the  blood  current  in  the  arteries  and  the  veins  of  the  region 
whose  vaso-motor  nerves  are  stimulated  or  paralysed  (manometr-ic  method). 
This  method  can  be  varied  by  measuring  and  registering  the  changes  of  volume 
of  the  region  whose  nerves  are  being  stvidied  (plethystnographic  method).  Both 
require  that  certain  controlling  facts  be  taken  into  account  by  which  it  is  possible 
to  distinguish  a  pm-ely  local  from  a  general  variation  of  the  circulation.  A 
method  which  has  been  highly  prized  for  the  study  of  the  determination  of  vaso- 
motor phenomena  consists  in  measuring  the  changes  of  local  temperature  corre- 
sponding to  tliese  actions  on  the  nervous  system  (thermometric  method)  ;  this 
method  is  very  untrustworthy  ;  the  changes  of  temperature  are  very  slow  in 
their  production  and  slow  m  dissipating,  and  they  depend  upon  multiple  and 
variable  conditions,  amongst  which  the  changes  which  ensue  in  the  local  circula- 
tion are  merely  an  isolated  factor. 

The  contractions  of  the  stomach  and  of  the  intestine  can  be  appreciated  and 
registered  bj'  the  aid  of  various  manometric  or  myographic  apparatus.  Slow 
movements  appertaining  to  isolated  cells,  such  as  those  of  the  chromatoblasts  of 
the  frog,  can  be  recognized  by  examining  under  the  microscope  a  transparent 
pigmented  area,  such  as  the  interdigital  membrane  [microscopic  method).  The 
alteration  of  the  general  tint  of  the  area  can  also  be  observed,  and  is  included  in 
the  colouriscopic  method. 

The  microscopic  method,  which  has  been  long  made  use  of  in  the  study  of  the 

P.  Y 


322 


SYSTEMATIC    FUNCTIONS 


circulation  in  transjoarent  organs  (especially  in  the  frog),  may  be  very  advan- 
tageously employed  for  the  special  study  of  the  vaso-motor  nerves. 

The  mechanical  phenomena  of  secretion  may  be  recognized  and  estimated,  like 
those  of  a  circulation  or  of  any  flow  of  fluid,  by  the  quantity  of  liquid  produced, 
and  its  pressure  in  the  conduits  in  a  given  time.  Chemical  phenomena  require 
confirmation  of  another  order,  such  as  the  dosage  of  the  substances  in  the  blood 
and  the  other  humours,  the  test  of  the  effect  of  ferments  upon  the  substances 
which  they  transform,  etc. 

4.     Systematization  of  the  great  sympathetic ;  its  two  orders  of  fibres  of 

projection 

The  great  sympathetic  is  formed  of  an  intra-rachidian  or  spinal  part 
and  of  an  extra-rachidian  or  ganghonic  portion,  united  the  one  to  the 


Gang.  Sp. 


Fig.    130. — Diagram  of  a  metamere,  with  its  myelomere  (completed  by  the  spinal  and 
sympathetic  ganglia),  its  dermatomere,  myomere  and  splanchnomere. 

Penetration  of  the  circulatory  portion  of  the  splanchnomere  into  the  dermatomere  and  the 
myelomere.  Circulatory  parallel  penetration  of  the  elements  of  the  great  sympathetic.  Mixture 
of  these  latter  with  the  conscious  voluntary  nerves  at  the  level  of  the  mixed  trunks. 


other  by  its  gangha.  These  form  two  wholes  comparable  to  those 
which,  in  the  animal  nervous  system,  connect,  the  one  the  brain  to  the 
cord,  the  other  the  cord  to  the  periphery.  Each  of  these  wholes  plays 
its  part  and  has  its  special  structure  in  both  of  these  systems  ;  but  if 
in  the  two  systems  the  arrangement  of  the  deep  nerves  differs  much, 
that  of  the  peripheral  nerves  is  very  similar.  Thus  we  once  again 
encounter,  in  connexion  with  the  great  sympathetic  and  its  ganglia 
the  question,  already  considered,  of  metamerism,  which  arises  once 
more. 

Ganglionic  Metamerism  and  Spinal  Metamerism. — As  regards  the 
roots  of  the  spinal  nerves,  we  have  drawn  a  marked  line  of  distinction 
between  the  radicular  metamerism  and  the  spinal  metamerism,  the 
first  being  obvious  and  the  other  reduced  to  a  mere  trace.     The  inter- 


CONSCIOUS  AND  UNCONSCIOUS  :  THEIR  SEPARATION    323 

vention  of  the  great  sympathetic  tends  still  further  to  upset  this  latter 
in  a  new  but  quite  as  complete  manner. 

The  ganglia  of  the  sympathetic  chain,  with  few  exceptions,  corre- 
spond, both  as  regards  number  and  situation,  to  the  mixed  trunks  of  the 
nerve  pairs  with  which  they  are  united  by  so-called  communicating 
branches.  These  ganglia,  which  have  embryological  and  even  func- 
tional connexions  with  the  spinal  ganglia,  thus  reproduce  the  primitive 
metamerism,  the  true  metamerism  ;  while  the  myelomeres  have  dis- 
appeared by  fusion  and  reciprocal  interpenetration,  they  have  remained 
distinct.  These  ganglia  of  the  chain  give  off  by  their  communicating 
branches  fibres  of  distribution,  which  follow  the  mixed  trunks  towards 
the  periphery  (these  are  the  grey  branches)  ;  on  the  other  hand,  they 
receive  from  the  spinal  cord  fibres  of  origin  by  these  same  communicat- 
ing branches  (these  are  the  white  branches).  But  these  fibres  of  spinal 
origin  do  not  come  from  the  pair  of  corresponding  roots,  they  arise  from 
roots  situated  either  above  or  below  the  corresponding  ganglion  ;  and 
in  order  to  do  this  they  follow,  in  the  chain  itself,  a  more  or  less  lengthy 
course,  during  which  they  usually  pass  over  a  certain  number  of  ganglia. 

If  they  are  intended  for  the  head  or  for  the  superior  hmb,  they  arise 
generally  from  the  roots  situated  below  those  which  are  continuous 
with  the  nerve  trunks  of  these  regions  ;  if,  however,  they  are  destined 
for  the  inferior  limb,  they  take  origin  from  roots  situated  above  those 
of  the  nerves  of  this  hmb.  This  is  the  result  of  what  has  been  said 
above  wdth  regard  to  the  condensation  of  the  origins  of  the  great  sym- 
pathetic in  the  thoracic  region  of  the  spinal  cord,  while  those  of  the 
principal  conscious  voluntary  nerves  are  found,  on  the  contrary,  in  its 
cervical  and  lumbar  enlargements. 

However,  besides  these  chief  origins  in  the  cord,  the  great  sympa- 
thetic has  others,  which  may  partially  coincide  with  those  of  the  nerve 
trunks  distributed  to  the  region  in  question.  For  example  :  the  sym- 
pathetic nerves  of  the  face  come  to  it  from  the  five  first  dorsal  roots, 
ascend  by  the  cervical  chain,  reach  the  trigeminal,  and,  by  its  branches 
and  ramifications  are  distributed  to  the  apparatus  and  organs  to  which 
they  belong ;  but,  further,  a  jDortion  of  these  nerves  proceeds  directly 
from  the  origins  of  the  trigeminal  themselves.  The  sympathetic  nerves 
of  the  foot  proceed  to  it  from  the  three  last  dorsal  and  the  two  first 
lumbar  nerves,  and  by  the  lumbar  chain  they  rejoin  the  trunk  of  the 
sciatic  nerve  ;  but,  further,  a  part  of  these  nerves  (by  far  the  smaller) 
arises  from  the  origins  of  the  sciatic,  that  is  to  say,  from  the  two  last 
lumbar  and  sacral  roots. 

Between  these  two  sites  of  origin,  one  principal  and  the  other  acces- 
sory, there  is  sometimes  a  very  wide  interval.     As  regards  the  sympa- 


324  SYSTEMATIC    FUNCTIONS 

thetic  nerves  of  the  face,  this  interval  extends  to  the  whole  length  of 
the  cervical  spinal  cord. 

Parallel  Systems  for  different  functions. — The  great  sympathetic 
assumes  or  directs  several  functions  :  movement  of  the  blood  in  the 
vessels,  formation  and  expulsion  of  secretions,  progression  of  the  ali- 
ments in  the  digestive  tube,  etc.  From  this  point  of  view,  it  may  be 
resolved  into  as  many  parallel  systems  as  there  are  distinct  functions 
or  species  of  cells  for  the  performance  of  these  functions.  These  systems, 
which  we  call  parallel,  are  so  in  the  strict  sense  of  the  word,  in  the  sense, 
namely,  that  from  their  origin  (spinal)  to  their  termination,  they  are 
strictly  superposable.  Example  :  the  ocular  apparatus  contains 
vessels,  glands,  and  deep  muscles  regulating  the  access  of  light,  which 
are  all  unconscious,  involuntary  organs.  Their  nerves,  supplied  by  the 
great  sympathetic,  take  their  origin  from  the  same  regions  of  the  spinal 
cord  and  bulb,  whether  they  are  vaso-motor,  secretory,  or  dilator  of  the 
iris,  etc.  These  origins,  entirely  superposable  between  sympathetic 
nerves  whose  functions  differ,  are,  as  is  obvious,  very  distinct  from 
those  of  the  conscious  voluntary  nerves,  which  supj)ly  the  ocular 
apparatus  with  sensation  and  movement. 

Aberrant  portions  of  the  medullary  segment. — In  order  to  recognize 
spinal  metamerism  under  its  primitive  form,  it  is  necessary  then,  in  an 
imaginary  manner,  to  add  to  the  spinal  cord  two  formations  situated 
outside  the  vertebral  canal  and  Avhich  in  fact  appertain  to  it,  namely,  the 
spinal  ganglia  and  the  sympathetic  ganglia.  Transverse  superposed 
planes,  ivhich  cut  the  spinal  cord  and  the  ivhole  body,  passing  through  the 
intervals  hetiveen  the  nerve  jjairs,  as  also  the  communicating  branches  and 
the  sympathetic  gariglia,  form  the  boundaries  of  a  series  of  partial  systems 
in  ivhich,  nevertheless,  all  the  essential  functions  of  the  nervous  system 
are  represented.  The  spinal  ganglia  and  the  anterior  cornua  of  the 
grey  matter  of  the  cord  represent  in  them  sensation  and  movement  of 
animal  life  v/ith  the  relations  which  they  form  together  in  the  most 
simple  reflex  acts.  The  ganglia  of  the  great  sympathetic  represent  in 
them,  by  themselves  alone,  the  sensation  and  movement  of  the  vege- 
tative life,  with  the  relations  which  they  effect  in  the  ganglionic  reflexes. 
These  two  associations  are  indeed  slightly  united  between  themselves 
(according  to  Dogiel),  by  the  fibres  of  union  which  exist  between  the 
cells  of  the  spinal  ganglia  and  those  of  the  ganglia  of  the  great  sym- 
pathetic. 

Association  of  the  Metameres  by  the  tracts  of  the  Spinal  Cord  and  the  connect- 
ing fibres  of  the  Chain. — In  brief,  it  is  apart  from  the  spinal  cord  projaerly  so 
called,  rather  than  in  it,  that  we  recognize  jDrimitive  metamerism.  The  fmiction 
of  the  cord  is  indeed  the  creation  of  associations  of  a  new  order  very  different 


CONSCIOUS  AND  UNCONSCIOUS  i    THEIR  SEPARATION    325 


Catenary        Intermed: 


from  those  existing  in  the  metameres.  It  associates  mutually  metamexes  of  the 
Hfe  of  relation  and  of  them  forms  groups  corresponding  to  definite  functions. 
It  is  not  under  the  necessity  of  associating  the  metameres  (ganglia)  of  the  vegeta- 
tive life,  because  this  association  is  effected  apart  from  it,  by  the  great  sympa- 
thetic chain,  which  becomes  by  its  connecting  fibres  the  equivalent  of  the  deep 
tracts,  or  those  of  association  of  the  spinal  cord.  On  the  other  hand,  it  associates 
amongst  themselves,  in  their  turn,  the  systems  of  animal  organic  life  ;  the  func- 
tions of  the  two  orders  being,  as  is  well  known,  reciprocally  dependent  and 
comjjelled  mutually  to  aid  one  another. 

By  examining  matters  from  this  point  of  view,  we  encoiuiter  under  a  ne^v 
form  the  original  difference  of  the  two  systems  knowTi  as  those  of  animal  and 
vegetative  life.  In  the  segments  of  the  juxta-ganglionic  spinal  cord  defined 
above,  we  recognize  once  more,  as  regards  the  roots,  the  medullary  origins  of  the 
nerves  of  the  life  of  relation  ;  in  these  same  segments  we  no  longer  find  the 
medullary  origins  of  the  corresponding  ganglia  of  the  great  sympathetic  ; 
to  meet  again  with  these,  it  is  necessary  to  seek  for  them  in  the  segments  situated 
above  or  below  ;  they  are  enclosed  almost  entirely  in  the  segments  of  the  thoracic 
spinal  cord  alone. 

In  reality,  these  two  orders  of  origin,  although  both  may  be  medullary,  are  in 
no  sense  equivalent.  The  condensation  of  the  medullary  origins  of  the  great 
sympathetic  in  a  special  region  of  the  grey  axis  indicates  that  they  correspond 
in  this  to  a  systematization 

of  the  second  degree,  where  Svinal  cord  Ganfia 

metamerism  has  almost 
disappeared.  The  gradu- 
ated arrangement  of  the 
motor  nuclei  of  the  skeletal 
muscles  implies,  on  the 
contrary,  a  systematiza- 
tion of  the  first  degree,  in 
which  me'amerism  is  re- 
cognizable. To  the  system 
of  vegetative  life  the  spinal 
cord  is  already  what  the 
medulla  oblongata,  the 
pons  and  the  cerebral 
ganglia  are  to  the  system 
of  the  life  of  relation.  The 
dissociation  in  height  of  the  two  systems,  which  is  so  obvious  between  their 
inferior  portions,  is  maintained  in  the  depth  of  the  nervous  system. 

Extension  of  the  Spinal  Cord  up  to  the  limit  of  the  Ganglionic  System. 
— In  principle,  we  maintain  that  the  great  sympathetic  is  formed,  in 
proceeding  from  the  spinal  cord  to  the  periphery,  by  two  neurons, 
placed  end  to  end  and  united  in  a  ganglion  ;  such  is,  diagrammetric- 
ally  represented,  its  characteristic  disposition.  Nevertheless,  we  notice 
that  its  brandies  traverse,  not  one,  but  generally  three  orders  of  suc- 
cessive ganglia,  which  may  be  distinguished  topographically  in  the 
following  manner  :  (1)  the  ganglia  of  the  chain  (or  vertebral),  (2)  the 
gangha  of  the  periphery  (terminal  ganglionic  plexuses),  (3)  the  ganglia 
occupying  an  intermediate  position  (in  the  same  way  as  the  coeliac  and 
mesenteric  ganglia).     There  are  reasons  for  thinking  that,  as  regards 


Fig.    1.31. — Extension   of   the   myeloniere  outside   the 
\ertebral  canal  (diagram). 

Spinal  cord,  ganglion  of  the  chain,  intermediate  and 
terminal  ganglia  belonging  to  the  same  metamere. 

Peripheral  neurons  in  blue  ;  deep  neurons  in  red. — Their 
principal  locality  of  union  is  in  one  of  the  ganglia  situated  in 
the  course  of  the  nerve. — Collaterals  distribute  the  impulse 
from  one  neiu-on  to  several  ganglia. 


326  SYSTEMATIC    FUNCTIONS 

a  given  fibre,  the  break  is  made  in  one  or  other  of  these  locahties,  but 
not  of  necessity,  and,  above  all,  not  totally,  in  the  three  successively. 
The  spino-ganglionic  neuron  has  received  different  but  equivalent 
names  {pre-ganglionic  fibre,  fibre  of  projection  of  the  second  order)  ; 
as  also  the  ganglio-peripheral  neuron  (post-ganglionic  fibre,  fibre  of 
projection  of  the  first  order,  etc.). 

Long  and  short  paths. — To  a  greater  or  lesser  degree  it  is  admitted  that  there 
is  a  rough  sketch  of  this  kind,  which  may  be  compared  to  that  of  the  voluntary 
nerves,  proceeding  from  the  cortex  to  the  skeletal  muscles,  by  two  orders  of  fibres 
of  projection,  united  in  the  grey  matter  of  the  spinal  cord.  On  this  primitive 
scheme  it  is  probable  that  complications  are  grafted  by  the  addition  of  com- 
missural inter-ganglionic  fibres,  comparable  to  the  fibres  of  association  mutually 
uniting  the  stages  of  the  cord.  Physiologists  have  denied  their  existence,  but 
no  decisive  exj^eriment  has  been  brought  forward  in  disjaroof  of  it.  As  to  the 
intra-ganglionic  elements  of  association,  they  are  evident.  The  sympathetic 
would  have,  then,  like  the  voluntary  system,  its  long  and  its  short  paths. 

Graduated  arrangement  of  the  ganglionic  relays. — This  graduated  arrange- 
ment of  the  grey  masses,  in  which  the  articulation  of  the  neurons  is  effected, 
explains  certain  apparently  contradictory  results  with  regard  to  the  degeneration 
of  the  sympathetic  nerves.  If  their  medullary  roots  be  cut,  these  nerves  are 
neither  entirely  degenerated,  as  Schiff  believed,  nor  entirely  preserved  through 
their  ganglia  as  Waller  thought  ;  but  the  branches  of  the  chain  to  which  they 
give  origin  present  a  mixture  of  healthy  and  degenerated  fibres,  of  which  some 
have  their  trophic  centre  in  the  ganglia  and  others  in  the  spinal  cord. 

This  graduation  appears  to  exist  as  regards  fibres  of  the  same  function.  If, 
in  the  skull,  the  facial  nerve  which  contains  the  origin  of  the  vaso-dilators  of  the 
tongue  be  cut,  and  if,  after  degeneration,  the  chorda  tymjoani  nerve  be  stimulated, 
the  vaso-motor  excitability  of  the  latter  is  observed  to  be  diminished,  but  not 
wholly  abolished  (Morat).  When  the  vagus  is  stimulated  in  the  horse,  it  some- 
times happens  that  the  cardiac  mviscle  is  tetanized,  as  would  be  the  case  with  an 
ordinary  muscle  (Arloing)  ;  it  is  possible  that,  in  this  case,  the  fibres  proceeding 
directly  to  the  myocardimn,  and  not  those  going  to  its  motor  ganglia  are  acted 
on. 

Lastly,  the  graduated  arrangement  of  the  terminations  of  the  neurons  in  the 
ganglia  which  follow  each  other  must  be  admitted  not  only  for  individually  dis- 
tinct neurons,  but  for  their  collaterals,  which  exhaust  themselves  the  one  after 
the  other  in  these  ganglia,  before  giving  their  terminal  branches  to  the  most 
remote  among  them. 

Constitution  of  the  Sympathetic  Chain. — These  ganglia,  placed  in 
succession  on  a  conducting  path  of  the  great  sympathetic,  do  not  exactly 
form  stages,  like  the  superposed  segments  of  the  spinal  cord,  but,  on 
the  contrary,  aw  extension  in  tvidth  of  the  myelomere  to  which  they 
belong.  It  is  quite  otherwise  with  the  ganglia  of  the  chain  which 
truly  indicate  the  metameric  swperjjosed  stages  of  the  great  sympathetic  ; 
each  of  these  stages,  in  order  to  perfect  itself,  adjoining  a  respective 
portion  of  the  terminal  plexus  and  of  the  intermediate  ganglia. 

As  the  sympathetic  fibres,  in  order  to  reach  their  branches  of  peri- 
pheral distribution,  generally  pursue  a  certain  vertical  course  in  the 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    327 


Centr.  G 


chain,  and  pass  through  a  certain  number  of  its  gangha,  the  same  ques- 
tion may  be  proposed  concerning  them  as  for  those  which  are  situated 
outside  it.     Between 

these  gangha,  which  ^'"'  ^^ 

are  those,  or  rather 
which  is  that  forming 
the  point  of  union 
between  the  spino- 
ganghonic  and  the 
gangho-peri  p  h  e  r  a  1 
neuron  ?  Is  it  that 
which  is  opposite  to 
the  nerve  pair  whence 
come  the  fibres  start- 
ing from  the  spinal 
cord  ?  Or,  more  pro- 
bably, that  which  is 
opposite  to  the 
branch  of  distribu- 
tion, and  which  con- 
veys the  fibres  to  the 
periphery  ?  Langley, 
who  has  studied  this 
question  in  detail, 
maintains  that  it  is  t^ 
the  ganglion  oppo- 
site to  the  branch  of 
distribution  (it,  or 
one  of  those  which 
follow  it  on  the 
branch)  which  in- 
dicates t  h'e  stage 
where  one  of  the  two 
neurons  ends  or  the 
other  begins.  Start- 
ing from  the  spinal 
cord,  the  spino- 
ganghonic  neuron 
first  follows  the  cor- 
re  spending  root, 
reaches  the  chain 
at    the  level  of  a    ganglion   (or  in  its  neighbourhood),   ascends  or 


132. — Diagrammatic    representation    of    the    great 
sympathetic  ;  structure  of  the  chain  (Soulie). 

Centripetal  neurons  in  blue  ;  centrifugal  neurons  in  red. 

In  the  motor  field  the  deep  neiu'ons  (medullo-gangUonic)  are 
in  red  lines  ;  the  terminal  neurons  (gangUo-peripheral)  are  in 
red  dotted  lines  ;    the  neurons  of  association  in  black. 


y 


J 


12S 


^YSTEXAliC  Fi::scEK»>cs 


one  T  .. 


5^ 


at  klie  iairi-  xSiaz  iir  has 


■r^LsCTjT  i?3«Hr  *n*iHT  et3Ts=pc:iids  tQ  T.htV  gsjic: 


ro  uii£~ 


IT  '-r  X . 


roan. 


■rUTOtAEm 


5r=^  Crimea  ct  rw> 


jrl,   ^RUtrv     T*T^^.     ~fr*—  '**W"  -^  ^'ITl*  J — ^^ 


^ilir  "^rcer 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION     329 


formed  by  the  vertebral  column,  the  peripheral  system  of  animal  life  has  its 
sensori-motor  j^rimary  nuclei  all  situated  internally,  while  those  of  the  peripheral 
system  of  the  vegetative  life  are  external  to  this  case. 

Completed  Myelomere. — This  dissociation  of  the  primary  nuclei  permits,  never- 
theless, the  persistence  of  their  primitive  metameric  disposition,  in  the  sense 
that  those  which  correspond  on  transverse  planes  (the  one  within,  the  other  with- 
out the  spinal  cokunn)  may  be  regarded  as  forming  part  of  the  same  myelomere, 
and  that  their  fibres  of  distribution,  mixed  in  the  mixed  trunks,  proceed  to  the 
same  dermatomere. 

Vertical  displacement  of  the  secondary  nuclei. — On  the  other  hand,  the  reci- 
procal displacement  of  the  secondary  nuclei  (sensori-motor  of  the  deep  systems) 
allows  the  persistence  of  scarcely  a  trace  of  primitive  metamerism,  for  which  it 


Spinal  cord, 


Spin,  gawji 


Fig.    133. — ^Voluntary  and  involiintarj-  nervous  systems. 

Diagram  pointing  out  their  essential  resemblance.  Peripheral  cycles  (metameric)  in  blue 
(spinal  nerves  and  branches  of  the  great  sympathetic).  Deep  cycles  (not  metameric)  in  red 
(columns  of  the  spinal  cord  and  of  the  sympathetic  chain).  The  arrows  represent  the  sensory 
and  motor  nerves  in  the  two  portions  of  the  two  systems. 

substitutes  a  new  organization,  in  which  the  two  sj-stems  assume  their  most 
pronoimced  respective  characters  and  their  most  characteristic  differentiation. 
This  displacement  is  no  longer  lateral,  but  in  the  direction  of  the  nerve  axis  (in 
the  vertical  direction  in  man). 

The  animal  system  has  its  superior  or  deep  centres  situated  in  the  skull,  ob- 
viously above  the  primary  centres.  In  the  vegetative  system  the  deep  centres 
are  in  the  vertebral  column  itself  (where  they  there  precede  its  primary  or  inferior 
centres)  and  no  longer  above,  but  within  its  strictly  primary  centres  (which  are 
in  the  ganglia  of  the  great  sympathetic),  no  longer  directly  opposite  to  these 
latter,  bvit  on  the  contrary  condensed  into  certain  definite  regions  of  the  grey 
medullary  axis  (chiefly  the  thoracic  region). 

Secondary  reinforcing  nuclei. — The  deep  nuclei  of  the  great  sympathetic  are 
condensed  in  the  thoracic  region  to  such  a  degree  indeed  that  there  are  few 
organs  with  which  this  region  is  not  connected  by  its  vegetative  nerves  (especially 
the  vaso-motors).  Nevertheless,  these  nuclei  are  foimd  also  in  two  other  regions 
of  the  gi"ey  medullary  axis,  namely,  as  regards  the  inferior  portion  of  the  body, 
in  the  lumbosacral  region,  as  regards  the  superior  portion,  the  bulbar  region.  The 
nerves  taking  origin  from  these  localities  do  not  throw  themselves  into  the  chain, 
but  sometimes  pass  it  by  and  proceed  to  remote  ganglia  or  plexuses  (erector, 
nerves  going  to  the  hypogastric  plexus  ;  pneumogastric  nerve  going  to  cardiac, 
pulmonary,  intestinal  plexuses,  etc.). 

Dissociation  of  the  two  Deep  or  Superior  Systems. — The  fibres  of  projection  of 
the  second  order  (fibres  of  the  two  deejD  systems,  animal  and  vegetative)  are 
thus,  from  this  fact,  altogether  separated.     Those  of  the  animal  system  form 


330 


SYSTEMATIC    FUNCTIONS 


an  important  portion  of  the  white  tracts  of  the  spinal  cord  ;  those  of  the  vegeta- 
tive system  form  an  equally  important  part  of  the  cords  of  the  sympathetic  chain. 
The  first  proceed  from  the  interior  of  the  skull  to  the  interior  of  the  spinal  column 
(or  conversely),  the  second  go  from  the  interior  of  the  spinal  column  to  some 
ganglion  external  to  it  (or  conversely).  The  first  form  a  fan  or  cone  with  a 
vertical  axis  (in  man)  spread  out  above  ;  the  second  form  a  fan  or  cone  with  a 
transverse  axis  expanded  outside. 

Metamerism  and  Symmetry. — The  two  peripheral  systems  (the  animal  and  the 
vegetative)  still  greatly  resemble  one  another,  in  the  sense  that  they  are  both 
metameric  (by  reproduction  of  the  same  parts)  and  symmetrical  (by  enlargement 
of  certain  of  these  portions  at  an  equal  distance  above  and  below  a  transverse 
plane  passing  through  the  middle  of  the  spinal  cord).  The  two  deep  systems  are, 
from  these  points  of  view,  very  different,  in  the  sense  that  the  animal  system,  in 
addition  to  not  being  metameric,  is  markedly  unsymmetrical  ;  while  the  vege- 
tative system,  which  has  equally  broken  with  metamerism,  still  preserves  a  sym- 
metrical arrangement  in  relation  to  the  transverse  p^ane  above  referred  to. 

Approximat.on  of  non-equivalent  Cen- 
tres.— The  displacements  which  are  thus 
produced,  between  the  primary  centres  in 
the  lateral  direction,  and  between  the 
secondary  centres  in  the  vertical  direc- 
tion, have  produced  the  effect  of  bringing 
both  together  into  the  same  neighbovir- 
hood  and  of  mixing,  though  partially,  in 
the  grey  medullary  axis,  the  deep  centres 
of  the  great  sympathetic  with  the  inferior 
centres  of  the  animal  sj'stem.  It  must 
be  remembered  that,  in  spite  of  their 
medullary  situation  and  their  proximity, 
they  are  in  no  sense  equivalent,  either  as 
regards  order  of  functions  or  of  centres 
in  the  performance  of  these  functions. 
Although  intercalated  the  one  with  the 
other,  they  are  not  the  less  distinct,  affect- 
ing, when  considered  separately,  a  topo- 
graphy which  is  sj^ecial  to  each  (reinforce- 
ment of  the  primary  centres  of  the  animal 
life  in  the  cervical  and  lumbar  regions  ; 
coalescence  of  the  deep  centres  of  the 
vegetative  life  in  the  thoracic  region). 
So  that,  for  a  given  area  (dermatomere), 
the  primary  or  inferior  centres  of  the  animal  system  will  he  situated  in  the  corre- 
sponding myelomere,  while  the  secondary  or  deep  centres  of  the  vegetative  system  will 
he  found  in  a  myelomere  which  is  sometimes  remote.  It  must  be  added  that,  as 
regards  this  sam3  given  area,  the  secondary  vegetative  or  deep  centres  which  represent 
its  different  vegetative  functions  (circulation,  etc.)  are  intimately  mixed  in  the 
segments  of  the  grey  axis  which  contain  them. 

The  Roots  ;  Selection  and  mixture  according  to  the  order  of  functions.— For 
the  same  reason,  the  medullary  roots,  whicli  emerge  from  the  spinal  column 
through  the  intervals  between  the  vertebrae,  also  contain  mixtures  of  the  primary 
neurons  of  the  inferior  animal  system  and  secondary  neurons  of  the  deep  vegeta- 
tive system.  As  regards  the  first  (animal  system),  they  are  distributed,  the 
sensory  exclusively  in  the  posterior  roots,  the  motor  exclusively  in  the  anterior 
roots  ;    as  regards  the  second  (vegetative  system),  this  tendency  remains,  but 


Fig.    134. — Voluntary  and  involuntary 
motor  systems. 

Diagram  showing  the  unsymmetrical 
arrangement  of  the  deep  origins  of  the 
first,  compared  with  the  symmetrical 
arrangement  of  those  of  the  second. 

Periplieral  neurons  (metameric)  in  blue 
deep  neurons  (not  metameric)  in  red. 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    331 

there  is  a  mixture  of  a  certain  number  of  motor  and  sensory  fibres  (as  there  is 
knoA^ai  to  be  a  mixture  of  the  fibres  of  the  two  functions  in  the  cortico-spinal 
tracts  of  the  superior  animal  system). 

The  Inter-central  elements  of  inhibition  ;  topographical  difference. — The 
animal  and  the  vegetative  sj^stem  both  contain  inMhitory  elements  ;  in  both, 
these  elements,  formed  by  inter-central  neurons,  are  necessarily  limited  to  the 
deep  or  superior  system.  The  intra-rachidian  situation  of  the  'primary  centres  of 
the  animal  system  causes  all  these  inhibitory  elements  to  take  refuge  in  the  cord  and 
the  brain  :  the  extra-rachidian  situation  of  the  primary  centres  of  the  vegetative 
system  causes  these  inhibitory  elements  to  emerge  with  the  medullary  roots  and  they 
are  observable  in  them  and  in  the  communicating  or  pre-ganglionic  brandies  of  the 
great  sympathetic. 


5.  Topographical  Determinations 

The  great  sympathetic  is  distributed  partly  to  the  rnuscuJar  fibres, 
partly  to  the  glandular  cells,  and  hence  includes  motor  elements  strictly 
so  called  and  secretory  elements.  As  regards  its  functions,  this  is  an 
elementary  and  primordial  division.  Whether  muscular  or  glandular, 
the  elements  which  it  controls  appertain  to  apparatus  performing 
distinct  functions  (vaso-motor,  intestino-motor,  sudoriparous,  muci- 
parous, lactiferous,  etc.).  This  is  still  a  functional  division,  but  a 
secondary  one.  \^^hetlier  primitive  or  secondary,  these  functions  are 
nevertheless  external  to  itself.  With  regard  to  the  mutual  internal 
relations  of  its  elements,  we  divide  them  into  immediate  and  ynediate, 
or  those  of  the  first  or  second  degree  ;  or,  again,  into  infra-ganglionic 
and  supra-ganglionic,  in  other  words,  infracentral  and  intercentral  ; 
and  in  this  second  category  (intercentral  elements),  we  distinguish 
excito-motor  and  excito-inhihitory  elements  ;  or,  again,  those  with  a 
positive  and  those  with  a  negative  action. 

Its  arrangement,  approximately  regular,  furnishes  us  also  with 
another  division  of  a  purely  topographical  order.  With  regard  to  the 
layers  of  the  blastoderm,  its  branches  of  distribution,  starting  from 
the  chain,  are  on  the  one  hand  visceral  and  on  the  other  cutaneous  or, 
in  other  words,  direct  (proceeding  to  their  termination  without  union 
with  other  nerves),  and  indirect  (mixing  in  the  mixed  trunks  with 
nerves  of  function  of  a  voluntary  conscious  order).  With  regard  to 
the  axis  of  the  body,  considering  it  apart  from  its  medullary  origins, 
we  find  it  affecting  further  characteristic  arrangements. 

Taking  origin  principally  in  the  thoracic  spinal  cord,  its  branches 
again  join  the  chain,  and  thence,  by  a  double  symmetrical  extension 
above  and  below,  are  distributed  to  all  parts  of  the  body  (after  section 
in  the  ganglia,  both  of  the  chain  and  of  the  triinks  given  off  from  it). 
Both  above  and  below,  they  meet  with  (by  tlie  chain  or  without  the 
chain)  reinforcing  elements,  supplied  by  the  bulbar  and  the  sacral 


332 


SYSTEiMATIC    FUNCTIONS 


region.  As  regards  a  plane  which  cuts  the  body  transversely  at  the 
level  of  the  eighth  or  ninth  thoracic  vertebrae,  there  is  thus  a  superior 
and  an  inferior  half  of  the  great  sympathetic,  which  are  repeated  with 
a  certain  symmetry. 

A.  Superior  Half. — This  portion  of  the  great  sympathetic  receives 


Fig.    13.3. — Vaso-motor  innervation  of  the  bueco-facial  region. 

gg.Sp,  spheno-palatine  ganglion  ;  gg.Ga,  Gasserian  ganglion  ;  gg.cs,  superior  cervical  ganglion  ; 
gg-ci,  inferior  cervical  ganglion  ;  gg.th,  first  thoracic  ganglion  ;  ma.s,  superior  maxillary  nerve  ; 
•pa,  palatine  nerves  ;  ma.i,  inferior  maxillary  nerve  ;  de.i,  inferior  dental  nerve  ;  sym.ce,  cervical 
sympathetic  ;  sym.cr,  its  cranial  prolongation  going  to  the  Gasserian  ganglion  ;  va.sym,  common 
triink  of  the  vagus  and  the  sympathetic  ;  an.Vi,  ansa  Vieussenii  ;  sym.th,  thoracic  sympathetic 
with  its  original  communicating  branches  of  the  dorsal  pairs  ;  V,  origin  of  the  trigeminal  ; 
Di,  first  dorsal  pair  (constrictor  filaments  in  blue,  dilator  in  red). 

its  spino-ganglionic  elements,  partly  from  the  spinal  cord,  partly  from 
the  medulla  oblongata. 

1.  Elements  of  medullary  origin. — The  superior  half  of  the  thoracic 
cord  supphes  origins  which,  by  the  sympathetic  chain,  terminate 
generally  in  the  gangha  of  the  base  of  the  neck  (middle  and  inferior 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    333 

cervical  in  man,  inferior  cervical  and  first  thoracic  in  animals).  In 
proceeding  from  one  to  the  other  of  these  two  gangha,  the  chain  breaks 
up,  embraces  the  sub-clavian  artery,  and  thus  constitutes  what  is  knowTi 
as  the  Ansa  Vieussenii.  The  whole  of  this  region  gives  off,  in  two 
principal  directions,  two  important  branches  which  proceed,  some  to 
the  thoracic  viscera,  others  to  the  superior  extremity.  Re-organized, 
the  chain,  under  the  name  of  cervical  cord,  traverses  the  whole  length 
of  the  great  vessels  of  the  neck,  passes  once  again  through  a  large 
ganglion  (superior  cervical  ganghon)  ;  then,  from  the  superior 
extremity  of  the  latter,  it  proceeds  to  the  Gasserian  ganghon  of  the 
trigeminal,  by  the  branch  of  which  it  reaches  the  ophthalmic, 
sphenopalatine  and  otic  gangha.  The  anastomosis  between  the 
superior  cervical  ganghon  and  the  trigeminal  may  be  regarded  as  the 
prolongation  of  the  chain,  the  cranial  cord  of  the  great  sympathetic 
(Morat). 

The  Ansa  Vieussenii  is  a  sort  of  nodal  point,  starting  from  which  the 
distribution  of  the  sympathetic  takes  three  directions  through  three 
groups  of  fibres,  one  for  the  head,  one  for  the  superior  limb,  one  for 
the  viscera  of  the  chest.  From  a  purely  descriptive  point  of  view,  this 
latter  group  is  direct,  which  merely  impHes  that  it  forms  no  anasto- 
mosis with  the  mixed  nerves  of  the  spinal  pairs  ;  the  two  others  are 
indirect,  meaning  that  their  elements,  emerging  from  the  chain,  follow 
(Avith  the  exception  of  some  fibres  proceeding  by  the  path  of  the  arteries 
to  the  anterior  and  posterior  brain)  the  path  of  the  mixed  bulbo- 
medullary  trunks,  those  of  the  brachial  plexus  for  the  superior  limb, 
those  of  the  trigeminal  for  the  face. 

First  Group  :  Sympathetic  innervation  of  the  head  and  neck. — All 
the  organs  of  the  head,  including  the  brain,  receive,  by  this  route,  a 
motor  influence  which  comes  to  them  from  the  thoracic  spinal  cord 
and  which  controls  the  functions  of  involuntary  movement  represented 
in  it.  This  is  well  seen  when  the  sympathetic  is  cut  or  stimulated  at 
any  point  in  this  long  course.  These  perturbations  may  indeed  be 
classed  as  oculo-pupillary,  vaso-motor  and  secretory. 

Oculo-pupillary  effects. — When  the  great  sympathetic  is  stimulated,  the  eye 
protrudes  and  separates  the  eyehds  (by  contraction  of  the  smooth  muscular 
fibres  of  the  capsule  of  Tenon  and  also  of  those  which  are  contained  in  the  eyelids)  ; 
the  pupil  dilates,  either  by  inliibition  of  the  motor  forces  which  contract  the  iris, 
or  by  stimulation  of  a  muscle  haA-ing  a  radiating  action  (muscular  layer  of 
Grynfeld). 

The  lens  is  also  flattened,  either  by  inhibition  of  the  ciliary  muscle,  or  bj- 
stimulation  of  an  antagonistic  muscle  which  may  also  exist. 

Vaso-motor  effects. — They  are  of  two  kinds  /  stimulation  has  vaso-constrictor 
or  vaso-dilator  effects  according  to  the  locality  under  observation,  the  animal 
operated  on,  and  the  region  in  which  the  great  sj'mpathetic  is  stimulated.     In 


334 


SYSTEMATIC    FUNCTIONS 


the  dog  the  following  division  is  observed.  Apart  from  stimulation  of  the  great 
sympathetic  in  the  neck,  constriction  of  the  vessels  of  the  conjunctivse,  of  the 
iris,  of  the  ear,  of  the  tongue,  of  the  epiglottis,  of  the  tonsil,  of  the  soft  palate 
is  caused  ;  and,  on  the  other  hand,  congestive  dilatation  of  the  vessels  of  the 
retina,  of  the  lips,  of  the  gums,  of  the  cheeks,  of  the  jDalatine  arch,  of  the  nose 
(skin  and  mucous  membrane),  of  the  tongue,  of  the  salivary  glands.  Stimula- 
tion of  the  great  sympathetic  acts  further  (according  to  circumstances,  in  one  or 
the  other  senses  indicated)  on  the  circulation  of  the  brain  and  on  that  of  the 
thyroid  gland.  On  opening  one  of  the  efferent  vessels  of  a  lymphatic  gland  of 
the  neck,  I  have  observed  the  flow  of  lymph  to  he  considerably  increased  during 
stimulation.  Whatever  opinion  may  be  held  concerning  the  action  (direct  or 
indirect)  of  the  nervous  system  on  the  lymphatic  ajjparatus,  it  is  obvious  that 
the  great  sympathetic  regulates  the  local  circulation  of  this  system,  as  it  regulates 
that  of  the  vascular  apparatus.  The  thyroid  gland  receives  its  vaso-motor  nerves 
from  the  superior  jDortion  of  the  thoracic  chain  by  the  cervical  cord.      Stimula- 


FiG.    136. — Trophic  disturbances  after  section  of  the  cervical  sympathetic  (Morat  and 

Doyon). 

On  the  left,  head  of  rabbit,  normal  appearance.     On  the  right,  inflammation  of  the  con- 
junctiva and  opacity  of  the  crystalline  lens. 


tion  of  the  thoracic  chain  causes  either  vaso-constriction  or  vaso-dilatation,  on 
account  of  the  mixture  of  the  two  orders  of  fibres  (Morat  and  Briau). 

Secretory  effects. —  Stimulation  of  the  great  sympathetic  gives  rise  to  secretion 
of  the  sudoriparous  glands  of  the  face  (clearly  visible  only  in  certain  animals), 
that  of  the  lachrymal  gland,  and  that  of  the  submaxillary  gland  (which  under 
this  influence  secretes  a  thick  and  viscous  saliva  differing  from  that  which  follows 
stimulation  of  the  chorda  tympani).  This  stimulation  modifies  the  intraocular 
tension  (probably  by  acting  on  the  internal  secretion  of  the  himiours  of  the  eye 
at  the  same  time  as  on  its  internal  circulation).  Section  of  the  cervical  sympa- 
thetic causes  a  hypersecretion  of  the  sweat  glands,  of  the  Meibomian  glands,  of 
the  conjunctiva  and  of  the  sebaceous  glands  of  the  lobe  of  the  ear,  phenomena 
which  have  not  a  very  definite  coimterpart  in  the  effects  of  stimulation,  but 
which  are  in  favour  of  an  inhibitory  action  attributable  to  certain  fibres  con- 
tained in  the  divided  nerve  trunk. 

Trophic  effects. — Alongside  of  these  secretory  modifications,  we  must  point 
out  once  again  as  distinct  phenomena,  though  fundamentally  of  the  same  category, 
distiu-bances  of  epithelial  desquamation  (Arloing),  cutaneous  ulcerations, 
opacities  of  the  lens  (Morat  and  Doyon),  all  of  which  have  been  observed  to  follow 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    335 

section  of  the  sj'inpathetic,  as  results  not  absolutely  invariable  but  fairly  frequent. 
These  distui'bances,  known  as  trophic,  should  be  regarded  as  a  secondary  more 
or  less  remote  effect  of  the  functional  disturbance  resulting  from  defective  inner- 
vation of  the  tissues  in  which  they  are  observed. 

In  order  to  increase  these  trophic  effects  of  paralysis  of  the  sympathetic, 
Angelluci  has  practised  removal  of  the  superior  cervical  ganglion  on  newly  born 
animals,  and  has  observed  as  the  result  of  this  operation  distiu^bance  of  develop- 
ment of  the  face,  of  the  skull  and  of  the  ball  of  the  eye,  and  alterations  of  their 
different  tissues.  These  clisttirbances,  varying  according  to  the  animal,  are  more 
marked  in  the  dog.  The  author  has  noted  an  aloj^ecia  of  the  face,  a  dystrophy 
of  the  bones  of  the  skull,  a  vicious  development  of  the  teeth,  a  reduction  in  the 
dimensions  of  the  cornea  and  of  the  sclerotic  :  the  ball  of  the  eye  has  shrunk 
about  a  millimetre  in  diameter.  There  is  at  the  same  time  simple  atrophy  and 
sclerosis  of  the  iris  and  of  the  choroid.  The  structvire  of  the  retina  is  preserved, 
and  sight  is  not  weakened.  The  vessels  present  dilatations  and  their  lumen  is 
narrowed  in  places.  The  endocular  tension  was  not  diminished,  or,  if  so,  has 
been  quickly  recovered. 

According  to  Floresco,  these  effects  are  onlj'  obtained  by  the  section  of  a  con- 
siderable length  of  the  nerve  or  by  the  ablation  of  its  ganglia  (both  conditions 
hindering  regeneration).  The  skin,  the  muscles,  and  the  eye,  undergo  an  arrest 
of  development.  The  thyroid  gland  and  the  suprarenal  capsules  become  slightly 
hyperlrophied. 

Paradoxical  motor  effect  ;  so-called  pseudo-motor  influence. — When  the 
hypoglossal  nerve  has  been  cut  on  its  course,  its  peripheral  end,  or  the  one  which 
proceeds  to  the  tongue,  degenerates  conformably  to  the  well-known  law  of  Waller ; 
it  consequently  becomes  inexcitable  after  two  or  tliree  days.  If  the  chorda 
tympani  of  the  same  side  be  exposed,  and  it  be  cut  and  its  peripheral  end  stimu- 
lated, a  new  phenomenon  arises  which  is  absolutely  inexplicable  in  the  present 
state  of  our  knowledge.  This  stimulation,  which  ordinarily  only  acts  on  the  vessels 
of  the  tongue  by  causing  thetn  to  dilate,  gives  rise  to  contractions  of  the  lingual  muscles 
themseves  (Philippeaux  and  Vulpian). 

These  contractions  are  much  feebler  than  those  excited  by  the  hypoglossal ; 
they  are  most  obvious  towards  the  fourteenth  day  after  section  ;  their  latent 
period  is  much  longer  ;  their  form  is  much  shorter,  and  they  can  scarcely  be 
rendered  evident  except  bj-  a  series  of  shocks  i^roducing  their  summation.  While 
the  hypoglossal  is  excitable  by  salt  water,  the  chorda  tjmpani  (or  the  lingual 
which  contains  it)  is  not  excited.  Nicotine,  which  does  not  act  on  the  hyj^oglossal, 
excites  these  new  contractions  when  it  is  injected  into  the  blood  (Heidenhain). 
The  paradox  consists  in  this  :  a  nerve  which  was  not  a  motor  nerve  of  the  tongue, 
has  become  motor  for  its  intrinsic  muscles  after  section  of  the  hypoglossal.  This 
nerve  comports  itself  as  a  nerve  of  organic  life.  Further,  the  phenomenon  is 
independent  of  the  circulation  ;  it  occurs  when  the  tongue  with  its  nerve  trunks 
is  detached  from  the  animal  (Morat). 

Rogowics  has  observed  that,  after  section  of  the  facial  nerve,  the  cervical 
great  sympathetic  also  assiunes  this  singular  property  as  regards  the  nerves  of 
the  lip.     This  pseudo-motricity  appears  to  be  peculiar  to  the  vaso-dilatory   nerves. 

2.  Elements  supplied  by  the  Bulb. — The  sympathetic  elements,  which 
from  the  thoracic  cord  are  distributed  to  the  head,  are  there  reinforced 
by  other  identical  functional  elements  contained  in  the  origins  of  the 
cranial  nerves,  as  are  the  preceding  in  the  origins  of  the  thoracic  nerves. 
The  trigeminal  supphes  oculo-pupillary  nerves  (dilator  of  the  iris  and 
accommodator  for  distant  vision),  a  nerve  for  the  middle  ear  (to  the 


338 


SYSTEMATIC    FUNCTIONS 


internal  muscle  of  the  malleus  or  tensor  tympani).  The  sympa- 
thetic nature  of  this  nerve  filament  is  proved  by  the  presence  in  the 
dog  of  a  very  obvious  ganglion  at  a  point  where  the  nerve  penetrates 
the  muscle.  The  trigeminal  supplies  vaso-motor  nerves  (dilators  for 
the  retina  and  the  face)  ;  it  supplies  secretory  nerves  (for  the  lachrymal 
gland,  etc.)  which  go  to  rejoin  the  preceding  in  the  Gasserian  ganglian. 


Fig.  137. — Vaso-motor  innervation  of  the  retina. 
gg.op,  ophthalmic  ganglion  ;  gg.Ga,  Gasserian  ganglion  ;  gg.c.s,  superior  cervical  ganglion  ; 
n.ci,  ciliary  nerves  ;  hr.op,  ophthalmic  branch  of  Willis  :  symp.cr,  cranial  prolongation  of  the 
sympathetic  ;  symp.cer,  cervical  symjaathetic  ;  vag.symp,  common  trunk  of  the  vagus  and  of 
the  sympathetic  ;  V,  origin  of  the  trigeminal  ;  D',  origin  of  the  first  dorsal  pair  ;  an.Vi,  ansa 
Vieussenii  ;J  n.ve,  vertebral  nerve  (constrictors  in  blue,  dilators  in  red). 

The  oculo-motor  nerve  supplies  oculo-pupillary  nerves  (constrictors  for 
the  sphincter  of  the  iris  and  for  accommodation  for  near  vision). 

The  facial  nerve  supplies  vaso-dilator  nerves  for  the  soft  palate  (great 
petrosal  and  posterior  palatine  nerves),  branches  for  the  tongue  and 
the  submaxillary  and  sublingual  glands  (chorda  tympani)  ;   it  supplies 


CONSCIOUS  AND  UNCONSCIOUS :  THEIR  SEPARATION   337 

secretory  nerves  for  the  soft  palate  and  the  submaxillary  and  the  sub- 
lingual glands  following  the  same  course  as  the  preceding  (the  saliva 
whose  secretion  is  excited  by  stimulation  of  the  chorda  tympani  is 
watery  and  limpid  compared  to  that  secreted  by  stimulation  of  the 
cervical  sympathetic).  This  same  nerve  gives  a  filament  for  the  muscle 
of  the  stapes,  whose  action  is  antagonistic  to  that  of  the  internal  muscle 
of  the  malleus. 

The  glosso-jihciryngeal  supplies  vaso-dilator  branches  to  the  posterior 


Fig.    138. — Vaso-motor  innervation  of  the  tongue. 

gg.ge,  geniculate  ganglion  of  the  facial  (VII)  ;  gg.pe,  petrosal  ganglion  of  the  glosso-pharjaigeal 
{gl.ph)  ;  gg.c.s,  superior  cervical  sympathetic  ganglion  ;  sy7n.ce,  cervical  sympathetic  ;  an, 
anastomosis  of  the  superior  cervical  ganglion  mth  the  hypoglossal  (hy)  ;  li,  lingual  ;  c.o,  chorda 
tympani  (constrictor  nerves  in  blue,  dilators  in  red). 

portion  of  tlie  tongue,  vaso-dilator  and  secretory  elements  to  the 
parotid  gland  (small  deep  external  petrosal  proceeding  from  the  jugular 
ganglion  of  the  glosso-pharyngeal  to  the  otic  ganglion). 

The  vagus  supplies  vaso-dilatory  and  secretory  elements  to  the 
larynx  by  the  laryngeal  nerves. 

Remark. — The  neurons  proceeding  from  the  medulla  oblongata 
which  are  thus  united  to  the  great  sympathetic  by  the  aid  of  the  cranial 
ganglia  of  the  latter,  are  fibres  of  projection  of  the  second  order,  supra- 
ganglionic,  intercentral.  It  should  be  noted  that  a  considerable  portion 
of  these  neurons  follow  sensory  nerve  trunks  (especially  the  trigeminal)  ; 

P.  z 


338 


SYSTEMATIC    FUNCTIONS 


they  are  the  equivalents  of  the  sympathetic  elements  which  leave  the 
cord  by  the  posterior  spinal  roots  at  the  level  of  the  plexuses  of  the 
extremities  ;  they  resemble  them  in  this  that,  on  the  one  hand  they 
are,  although  centrifugal,  mixed  with  sensory  fibres  ;  and  on  the  other, 
that  they  take  their  origins  in  the  grey  axis  at  the  same  level  as  the 
nerves  discharging  sensory  functions  in  the  regions  to  which  they  are 
distributed. 

Another  portion  of  these  reinforcing  elements,  that  which  is  repre- 
sented by  the  facial,  the  glosso-pharyngeal,  and  the  vagus,  has  a  further 
characteristic  :   that,  namely,  of  avoiding  the  sympathetic  chain  itself, 


Fig.    139. — Vaso-inotor  innervation  of  the  sub-maxillary  gland. 
gl.s.m,   sub-maxillary  gland   and  its  excretory   duct  ;    gg.s.ni,   sub-maxillary   gland  ;    gg.c.s, 
superior  cervical  ganglion  ;     gg.ge,  geniculate    ganglion  ;     ra.gl,    intraglandular  ramifications  ; 
ra.sym,  cranial  sympathetic  ;    sym.c,  cervical  sympathetic  ;    co.ty,  chorda  tympani  ;    VII,  facial 
(constrictors  in  blue,  dilators  in  red). 

and  of  rejoining  the  sympathetic  elements  in  the  remote  or  terminal 
ganglia.  We  shall  encounter  an  arrangement  of  the  same  kind  in  the 
inferior  half  of  the  great  sympathetic  ;  it  is  that  of  the  erector  nerves 
which,  starting  from  the  sacral  cord,  cross  the  chain  without  entering 
it  and  lose  themselves  in  the  hypogastric  plexus. 

Second    Group :     sympathetic    nerves     of    the    superior    limb.  —  They 
have  nearly  the  same  medullary  origin  as  those  of  the  head.     Their 


CONSCIOUS  AND  UNCONSCIOUS :  THEIR  SEPARATION  339 

ganglionic  origin  is  indicated  by  the  stellate  or  first  thoracic  ganglion  ; 
from  this  ganghon  they  pass  through  the  vertebral  nerve  (and  also 
through  the  subjacent  communicating  branch)  in  order  to  rejoin  the 
brachial  plexus. 

Vertebral  Nerve. — The  condensation  of  the  gangUa  of  the  inferior  cervical  and 
superior  thoracic  region  into  a  single  mass  (stellate  ganglion)  necessitates  the 
condensation  of  the  conmiunicating  branches  which  correspond  to  it  into  a  single 
nerve  trunk,  the  vertebral  nerve.  Starting  from  this  ganglion,  the  nerve  re- 
ascends,  crossing  over  the  origins  of  the  bracliial  plexus,  and  gives  to  each  of 
them  a  filament  representing  its  commvuiicating  branch.  The  name  vertebral, 
given  to  this  nerve,  is  due  to  its  sitviation  and  to  its  com'se  in  the  costo-transverse 
foramina  of  the  cervical  vertebrae,  tliroughout  the  length  of  the  vertebral  artery, 
which  it  accompanies  and  to  which  it  supplies  ramifications,  as  also  to  its  branches 
and  terminations. 

The  vertebral  nerve  is  formed  for  the  greater  jaart  by  grey  non-myelinated 
fibres,  which,  functionally,  are  fibres  of  distribution  (efferent),  in  other  words, 
fibres  (motor)  of  projection  of  the  first  order.  Of  these  fibres  some  throw  them- 
selves directly  on  the  vertebral  artery,  thus  coi'responding  to  the  direct  or  visceral 
arteries  properly  so  called,  which,  from  the  ganglia  of  the  chain,  proceed  to  the 
larger  viscera  ;  the  others  attach  themselves  to  the  branches  of  distribution  of 
the  brachial  plexus,  thus  corresponding  to  the  indirect  branches  which  go  to  the 
vessels  and  the  glands  of  the  skin  by  way  of  the  cutaneous  nerves.  These  last 
are  a  mixture  of  vaso-motor,  secretory  and  pilo-motor  elements  intended  for  the 
corresponding  apparatus  which  is  situated  in  the  skin  and  also  for  the  vessels 
of  the  muscles  of  that  area. 

Whether  direct  or  indirect,  these  nerve  branches  are  a  mixture  of  elements, 
the  one  excitatory  and  the  other  inhibitorj^  for  corresponding  fimctions.  As 
regards  vaso-motor  fvmction,  they  contain  constrictors  and  dilators  of  the  vessels  : 
this  is  proved  experimentally  by  the  production  of  local  changes  in  the  circula- 
tion in  the  corresponding  ILinb  and  in  the  vertebral  artery  (Fran9ois-Franck). 

The  spinal  origins  of  the  vertebral  nerve  are  situated  in  the  thoracic  roots, 
from  the  second  to  about  the  sixth  or  eighth.  Having  left  the  cord  by  the  corre- 
sjDonding  roots  and  commvuiicating  branches,  they  ascend  the  thoracic  chain  of 
the  sympathetic  and  become  articulated  (partially  at  least)  in  the  stellate  ganglion 
with  the  fibres  of  distribution.  They  are  motor  neurons  of  the  second  order, 
just  as  the  preceding  are  the  motor  nevirons  of  the  first  order.  In  somewhat  the 
same  way  the  thoracic  nerves  give  off  fibres  which  (after  or  without  interruption) 
are  received  by  the  cervical  nerves  of  the  brachial  plexus  in  order  to  proceed  with 
it  to  the  periphery.  Do  the  roots  of  the  brachial  plexus  do  the  same  in  the 
opposite  sense  ?'  Do  they  give  motor  fibres  to  the  vertebral  nerve  and  to  the 
sympathetic  chain  which  the  latter  afterwards  distribute  ?  If  this  is  so  the 
number  thereof  is  very  limited. 

Sensory  fibres. — The  origins  of  the  brachial  plexus  thus  contain  few  or  no 
centrifugal  fibres  of  sjmipathetic  nature  ;  but,  according  to  Fran9ois-Franck, 
they  contain  centripetal  or  sensory  fibres  conveying  impressions  coming  from  the 
viscera,  which,  following  the  sympatlietic  chain  and  the  vertebral  nerve,  pene- 
trate into  the  spinal  cord,  whence  they  are  capable  of  reacting  in  the  form 
of  generalized  reflex  vaso-motor  effects,  manifesting  themselves  as  defensive 
reactions,  therefore  as  manifestations  of  conscious  sensibilitj*.  Accordmg  to 
Fran9ois-Franck,  these  effects  would  not  be  the  consequence  of  arterial  spasm 
of  the  vertebral  artery  and  of  the  cerebral  ansemia,  which  is  the  consequence  of 
it,  but  a  direct  sensory  effect. 


340 


SYSTEMATIC    FUNCTIONS 


oji.VL.^ 


SymJh i  .. 


V 


..11...  x'-z^  -^-/-'fd.br. 

L-   V       k  / 


^^vj 


Third  Group  :    visceral  tlioracic  nerves. From  the    ganglia  of  the 

base  of  the  neck  (inferior  cervical  and  first  thoracic  in  animals)  and 
from  the  Ansa  Vieussenii,  fibres  arise  which  proceed  to  the  gangha  of 
the  heart  and  to  the  ganglia  (plexiform)  of  the  lung.  Those  which  go 
to  the  heart  are  accelerators  of  its  movements.  Their  stimulation  has 
not  the  tetanizing  effect  of  that  of  ordinary  motor  nerves  ;    they  do 

_^  not    proceed 

/A 


strictly  to  the 
heart  muscle, 
but  to  its  motor 
ganglia,  whose 
special  action 
they  stimulate. 
To  these  gan- 
glia other  fibres 
also  proceed 
which  have 
taken  origin  in 
the  pneumogas- 
tric,  and  which 
exert  on  them, 
and  therefore 
on  the  heart,  an 
inhibitory  influ- 
e  n  c  e .  They 
clearly  enter 
into  the  forma- 
tion of  the  great 
symp  a  t  h  e  t  i  c 
system,  of 
which  they  are 
aberrant  e  1  e- 
ments  ;  they  are  further  mixed  with  some  accelerating  fibres  having 
the  same  origin. 

Like  the  ganglia  of  the  heart,  the  pulmonary  plexus  receives  fibres 
both  from  the  great  sympathetic  and  the  pneumogastric.  The  func- 
tions to  be  fulfilled  are  here  more  numerous,  the  lung  possessing,  in 
addition  to  its  intrinsic  muscles,  vessels  and  glands.  The  bronchial 
muscles  may  be  stimulated  and  also  inhibited  by  elements  coming  from 
the  pneumogastric.  The  pulmonary  vessels  receive  constrictors  coming 
from  the  great  sympathetic  ;  the  innervation  of  the  glands  is  imper- 
fectly known. 


ivm 


Fig.    140. — Medtillary  origin  and  distribution  of  the  ganglionic 
motor  nerves  of  the  thoracic  Hmb. 

Vaso-motor  nerves  in  red  ;    sweat  nerves  in  yellow. 

The  branches  of  origin  are  furnished  by  the  thoracic  spinal  cord 
and  follow  the  chain  ;  the  branches  of  distribution  follow  the  vertebral 
nerve  nv,  in  order  to  join  the  bracliial  plexus. 


CONSCIOUS  AND  UNCONSCIOUS  :  THEIR  SEPARATION    341 

B.  Inferior  Half. — From  the  inferior  portions  of  the  thoracic  and 
superior  portions  of  the  lumbar  cord  fibres  proceed  by  communicating 
branches,  which  rejoin  the  lumbar  chain  ;  they  follow  this  chain  in  a 
descending  direction  as  far  as  the  caudal  extremity,  where  they  ter- 
minate. These  are  the  diminished  equivalent  of  the  group  which  in  the 
superior  half  goes  to  the  head.  In  the  locality  where  the  chain  crosses 
the  lumbo-sacral  plexus,  it  provides  it  with  branches  of  distribution 
going  to  the  inferior  limb  ;  this  is  the  repetition  of  what  we  have  already 
seen  in  the  brachial  plexus.  Finally,  from  a  large  extent  of  the  dorsal, 
and  from  the  superior  part  of  the  lumbar  spinal  cord,  important  branches 
are  detached,  which  go  to  the  abdominal  viscera  :  this  is  a  third  group 
and  comprises  direct  or  visceral  elements  properly  so  called.  As  for 
the  origins  and  strengthening  elements,  they  also  are  not  lacking  here  : 
we  find  them  in  the  lumbo-sacral  spinal  cord,  furnishing  them  directly 
to  the  sacral  plexus  which  supplies,  in  addition,  the  erector  nerves, 
terminating  in  the  hypogastric  plexus. 

First  or  Caudal  Group. — This  is  represented  by  a  few  vaso-motor^ 
pilo-motor,  and  secretory  elements,  for  the  vessels,  the  hairs  and  the 
glands  of  the  skin. 

The  tail  in  animals  forms  a  series  of  metameres  (but  not  very  recog- 
nizable) which  prolong  those  of  the  trunk  (the  limits  of  the  latter  being 
distinctly  fixed).  On  the  contrary,  to  the  whole  length  of  the  latter, 
to  each  ganglion,  a  cutaneous  area  corresponds. 

Sympathetic  nerves  of  the  trunk. — If  we  take  the  trunk  as  a  whole,  we  see  that 
to  each  gangHon  a  series  of  spinal  origins  correspond  which  are  only  exceptionally 
on  the  same  level  as  themselves.  The  portrayal  of  these  correspondences,  which 
is  too  long  to  describe,  will  be  more  easilj^  represented  by  a  diagram.  The  dia- 
gram may  be  specially  based  on  indications  furnished  by  erection  of  the  fur  when 
the  pre-  and  post-ganglionic  branches  of  the  sympathetic  chain  are  stimulated. 

It  must  not  be  forgotten  that  the  first  thoracic  or  stellate  ganglion  corresponds, 
not  only  to  the  inferior  cervical  region,  but  also  to  the  commencement  of  the 
thoracic  region.  Thus,  it  is  more  especially  in  the  inferior  half  of  the  body  that 
the  metameric  ganglionic  arrangement  pointed  out  above  is  once  more  met  with. 

Second  Group,  or  that  of  the  Lower  Limb. — This  has  its  orgins  in  the 
spinal  cord,  from  the  tenth  or  eleventh  dorsal  as  far  as  the  second 
lumbar.  It  contains,  like  the  preceding,  vaso-7notor,  pilo-motor 
and  secretory  (sudoriparous  and  sebaceous)  elements.  Here  the  vaso- 
motor elements  are  some  constrictors,  and  others  dilators  of  the 
vessels  ;  sometimes  one,  and  sometimes  the  other,  are  more  easily 
demonstrable. 

Experiment. — If  the  dorsal  sympathetic  chain  be  stimulated  immediately 
above  the  diaphragm,  the  arterial  pressm-e  is  seen  to  be  locally  raised  in  the 
corresponding  inferior  limb,  this  being  due  to  the  fact  of  the  equally  localized 


342 


SYSTEMATIC    FUNCTIONS 


constriction  of  most  of  the  vessels  of  this  hnib  :  tliis  proves  the  existence  of  con- 
strictor nervous  elements.  At  the  same  moment  the  skin,  and  especially  the 
digital  pulp,  will  be  observed  to  be  markedly  reddened  by  the  afflux  of  blood  : 
this  is  proof  of  the  existence  of  dilator  elements  for  the  cutaneous  covering. 
If  the  stimulation  is  brought  to  bear  on  the  lunibar  chain,  and  especially  on  the 
trunk  of  the  sciatic  nerve,  the  constrictive  effect  with  regard  to  the  deep  vessels 
remains  quite  as  distinct,  but  the  dilator  cutaneous  effect  becomes  inconstant. 
Stimulation  of  the  sciatic  nerve  in  the  eat  always  produces  pallor  of  the  in- 
tegiuiient   (Dastre  and  Morat).     These  excitations  both   of  the  dorso-lumbar 

chain  and  of  the  sciatic 
nerve,  which  receives 
its  fibres  of  distribu- 
tion, produce  secretion 
of  the  cvitaneous 
sudoriparous  glands 
(Luchsinger). 

These  elements  of 
dorso-lumbar  origin 
are  reinforced  by 
other  arising  from  the 
sacral  spinal  cord,  and 
consequently  mixed 
with  the  origins  of 
the  sacral  plexus. 
The  secretory  fibres 
having  this  origin 
leave  by  the  anterior 
roots  of  the  sciatic 
nerve.  The  v  a  s  o  - 
motor  fibres  emerge 
with  the  'posterior 
roots,  and  are  exclu- 
sive 1  y  vaso-dilator. 
There  are  no  p  i  1  o- 
motor  fibres  having 
this  origin. 


the 


Fig.      141. — Medullary     origin     and     distribution     of 
ganglionic  motor  nerves  of  the  abdominal  limb. 

Vaso-motor  nerves  in  red  ;  sudoriparous  nerves  in  yellow. 
With  some  few  variations,  the  origins  and  the  distribution  of 
the  involuntary  nerves  of  different  functions  are  practically  the 
same. 


Third  Group,  or 
that  of  the  Abdominal 
Viscera. — T  his  is 
highly  important, 
on  account  of  the 
large  number  of  organs  to  which  its  branches  of  distribution  repair. 
In  order  to  construct  a  natural  group,  its  origins  must  be  started 
from  a  point  a  little  above  that  used  to  divide  the  great  symj)athetic 
into  its  two  halves. 

Elements  of  spinal  origin. — This  group  arises,  throughout  a  great 
length,  from  the  thoracic  spinal  cord,  and  also  from  the  superior  portion 
of  the  lumbar  region  of  the  same.  Its  origins,  after  having  come  into 
contact  with  the  chain,  leave  it  under  the  form  of  trunks  more  or  less 
condensed,  namely,    the  splanchnic  nerves,  large  and    small,  which 


CONSCIOUS  AND  UNCONSCIOUS :  THEIR  SEPARATION  343 

from  the  chain  run  to  the  coeliac  ganglion,  to  the  solar  plexus  and  to  the 
renal  plexus  ;  the  mesenteric  nerves,  which  from  the  chain  end  in  the 
superior  mesenteric  ganghon,  and  after  having  passed  through  it  proceed 
to  the  hypogastric  plexus. 

Elements  of  bulbar  and  sacral  origin. — The  coeliac,  superior  mesen- 
teric and  hypogastric  ganglia  are  mutually  united  by  links  parallel  to 
the  sympathetic  chain.  These  gangha  form,  in  a  way,  a  second  chain, 
anterior  to  that  following  the  lumbar  column.  For  this  reason  it  is 
sometimes  called  the  pre-vertehral  chain,  in  contrast  to  the  chain  pro- 
perly so-called,  which  is  named  vertebral  (Langley).  This  second  chain 
receives  strengthening  elements  by  two  very  remarkable  paths  :  the 
first  is  that  of  the  pneumogastric,  which  brings  it  the  bulbar  influence  ; 
the  second  is  constituted  by  the  erector  nerves,  which  convey  to  it  the 
influence  of  the  sacral  region. 

The  pneumogastric  gives  off  on  each  side  (but  especially  on  the  right) 
an  anastomatic  branch  to  the  coeliac  ganglion,  and  by  it  enters  the  solar 
plexus  and  extends  perhaps  as  far  as  the  pelvis.  The  sacral  7ierves 
cross  the  vertebral  ganglionic  chain  and  throw  themselves  into  the 
hypogastric  plexus.  Once  more  we  find  a  kind  of  symmetrical  arrange- 
ment above  and  below,  and  this  may  be  pointed  out  as  characteristic 
of  the  vegetative  nervous  system.  It  must  be  noted  that  this  sym- 
metry has  nothing  geometrical  about  it.  The  bulbar  influence  has,  in 
comparison  with  that  of  the  sacral  nerves,  an  extremely  extensive  field 
of  action.  From  this  fact  the  vegetative  nervous  system  at  this  stage 
displays  a  tendency  to  polar  dyssj^mmetry,  which,  in  the  animal  nervous 
system,  becomes  emphasized  in  the  highest  degree  by  the  development 
of  the  brain. 

Abdominal  viscera  and  those  of  the  pelvis  :  Corresponding  nervous  groups. — 
The  group  of  abdominal  viscera  niaj'  itself  be  divided  into  two  regions  :  the  one 
abdominal  properly  so  called,  comprising  the  stomach,  the  small  intestine,  the 
liver,  the  pancreas,  the  spleen  and  also  the  kidney  at  its  bovmdary  ;  the  other 
filling  the  pelvis  comprehends  the  bladder,  the  rectum,  the  anus,  and  the  genital 
organs.  To  these  two  visceral  regions,  nervous  trunks  and  distinct  ganglionic 
plexuses  correspond.  Connected  with  the  first  are  the  splanchnic  nerves,  which 
pass  into  the  coeliac  ganglion  and  the  solar  plexus,  before  arriving  at  their  destina- 
tion in  the  viscera  ;  and  with  the  second  the  mesenteric  nerves  which,  after  hav- 
ing passed  through  the  ganglion  or  mesenteric  plexus,  fall  into  the  hypogastric 
plextus,  before  reaching  then-  visceral  terminations.  The  coeliac  plexus,  as  has 
just  been  remarked,  receives  from  the  pneumogastric  elements  which  are  in 
general  antagonistic  to  those  of  the  splanchnic,  with  which,  however,  they  are 
connected  in  this  ganglion.  Tlie  hypogastric  plexus  receives  elements  from  the 
sacral  pair  (erector  nerves),  also  in  general  antagonistic  to  the  mesenteric  nerves, 
but  connected  with  them  in  this  plexus.  These  two  systematic  groups  are,  how- 
ever, not  isolated,  but  attached  to  each  other  by  connecting  links  as  well  as  to 
the  organs  which  are  innervated  by  them.  From  a  fvmctional  point  of  view 
they  present,  in    spite  of    being  grouped  together,  a  certain  difference  which 


344 


SYSTEMATIC    FUNCTIONS 


sejjarates  them,  and  in  the  same  groujjing  a  certain  conformity  which  ch-aws  tliem 
together.  In  the  superior  group  the  functions  are  durable  or  continuously 
rhythmical  ;  in  the  inferior  they  are  widely  intermittent,  as  indeed  is  appro- 
jjriate  for  reservoirs  which  preserve  contents  eventually  to  be  expelled. 

Functional  antagonism  between  elements  of  different  origin. — Tlie  special 
convergence  of  the  branches  of  tlie  })neumogastric  and  of  the  symjjathetic  on 
the  visceral  ganglia  has  been  already  pointed  out  with  regard  to  the  heart  and 
the  lung  in  the  superior  half.  It  is  functionally  remarkable  on  account  of  the 
fact  of  an  antagonistic  action  being  exercised  by  these  two  nerves  on  these  ganglia, 
or  at  any  rate  on  the  organs  depending  on  them.  For  the  cardiac  muscle  the 
pneumogastric  is  the  moderator,  and  the  sympathetic  the  accelerator  of  the 
movements.     As  concerns  the  gastric  muscles  (and  also,  but  less  evidently,  the 


Injer.  cerv  g. 


jj.         Aii'^a  Vieii'-enmi 


j;.  pn.  J.  n. 


CEsopli 


Or.  splanch.  _,  _  ^ 

I 

Small  sp!anch.  , 
Diaph.  plex.  ..  1, 


Fig.   142. — Sympathetic  and  pneumogastric  in  the  thoracic  region. 
Cardiac  nerves  and  splanchnic  nerves. 


\     \  .,  Lejl  pn.  g.  nerve 


^'omach 

Semi-lunar  G. 
Pie  v.  cixl. 


intestinal),  the  pneumogastric  augments  and  the  symj^athetic  inhibits  their 
tonic  or  peristaltic  contraction.  From  one  organ  to  another  this  antagonism  is 
again  met  iviih,  but  the  characters  are  inverted.  From  this  it  may  be  seen  that  one 
fxuiction  alone,  whether  it  be  motor  or  inhibitory,  is  not  attached  to  either  one 
or  another  of  these  groups,  any  more  than  to  the  grey  nuclei  whence  they  arise. 
However,  it  is  demonstrable  that  soixie  of  these  nerve  trunks  contain  elements 
fulfilling  both  functions,  and  in  this  case  action  in  one  or  the  other  sense  results 
sinnaly  from  the  predominance  of  either  motors  or  inhibitors  according  to 
circumstances. 


CONSCIOUS  AND  UNCONSCIOUS :  THEIR  SEPARATION    345 


99' 


Innervation  of  the  digestive  tube. — The  digestive  tube  is  innervated  from  the 
pharynx  (and  even  the  mouth,  as  concerns  its  vessels  and  glands)  by  the  branches 
of  the  great  sjanpathetic  and  equivalent  nerves.  Like  that  of  the  skin,  this 
innervation  answers  to  tliree  orders  of  functions  (motor,  vaso-motor  and  secre- 
tory). The  great  sympathetic  fm-nishes  secretory  and  vaso-motor  fibres  to  the 
salivary  glands,  in  concrurence  with  the  nerves  of  bulbar  origin. 

Many  authors  have  endeavomed  to  define  the  numbers  of  origin  of  the  spinal 
nerve  pairs  which  furnish  the  nervous  elements  proceeding  to  the  different  seg- 
ments of  the  digestive  tube  and  its  appendant  glands.  They  are  vmanimous 
with  regard  to  those  of  these  nerve  pairs  which  represent  the  principal  origins 
of  the  elements  destined  for  these  viscera.  This  unanimity  ceases  when  it 
becomes  a  question  of  exactly  defining,  either  above  or  below,  the  medullary 
territory  corresponding  to  these  origins  ;  some  increasing  and  others  diminishing 
its  extent,  either  in  one  or  the  other  direction.  This  arises  from  the  fact  that 
the  medullary  territory,  more  condensed  in  its  medium  or  cenrtral  portion^ 
becomes  diffused  and  lacks  clearly 
defined  limits  towards  its  extremi- 
ties. These  divergent  results  maj^ 
be  explained  by  individual 
anatomical  differences,  or  by 
differences  of  excitability  in  these 
elements  reduced  to  mere  traces  ; 
or,  finally,  by  variations  in  the 
■delicacy  of  the  methods  of  observ- 
ation made  use  of. 

The  (Bsophagus  receives  its  motor 
nerves  principally  from  the 
pneumogastric.  This  channel  in 
the  dog  receives  an  important 
branch  of  the  superior  cervical 
ganglion  of  the  great  sympathetic, 
as  Espezel  has  noticed.  Here  is 
a  new  proof  of  the  community  of 
natau"e  of  these  two  nerves. 

The  stomach  receives  nerves  both 
from  the  vagus  (motor)  and  from 
the  splanchnics  (inhibitory)  ;  the 
origins  of  these  latter  extend  from 
the  fifth  to  the  eighth  thoracic 
vertebrae. 

The  intestine  is  also  imier\'ated 
{at  least  as  regards  its  superior 
portion)  by  the  vagus  (motor)  and 
by  the  splanchnics  (inhibitory)  con- 
currently. 

The  stomach  and  the  intestine  receive  their  vaso-motor  nerves  from  the  two 
above-mentioned  nerve  trmiks.  As  regards  the  intestine,  the  origins  of  these 
nerves  extend  from  the  fifth  thoracic  as  far  as  the  second  kmibar.  The  eleventh, 
twelfth  and  thirteenth  thoracic  nerves,  as  well  as  the  two  first  Imnbar,  contain 
dilators  mixed  with  the  constrictors.  As  ganglionic  nerves  of  different  fvmctions 
have  obviously  the  same  origins,  we  can  make  use  of  these  determinations  to 
fix  the  sovu-ces  of  origin  of  the  ner\'Ous  system,  as  well  for  the  stomach  as  for  the 
intestine. 

In  principle  it  may  also  be  admitted  that  the  secretory  nerves  arise  from  the 


Fig.  143. — Innervation  of  the  intestine  in  the 
dog. 
pn.g,  pneumogastric  ;  qil.coe,  ccsliac  plexus  ; 
gg.m.s,  superior  mesenteric  ganglion  ;  gg.  m.i,  in- 
ferior mesenteric  ganglion  ;  Pl.hyp,  hypogastric 
plexus  ;  g.sp,  great  splanchnic  ;  n.er,  erector 
nerve  ;  Dxiii,  tliii-teenth  dorsal  pair  ;  Liii,  third 
lumbar  pair  ;  Si,  first  sacral  pair. 


346  SYSTEMATIC    FUNCTIONS 

same  regions  at  the  same  time  as  from  the  vagiis,  bvit  the  study  of  these  nerves 
is  far  less  advanced. 

The  pancreas  also  receive  a  double  innervation  from  the  pneumogastric  and 
from  the  great  sympathetic.  For  it  also  branches  are  detached  from  the  spinal 
cord,  from  the  fifth  or  sixth  thoracic  to  the  second  lixmbar.  Its  vaso-dilators 
reach  it  principally  from  the  vagus ;  there  are  a  very  small  nmnber  of  them  in 
those  branches  of  the  great  sympathetic  which  are  destined  for  it.  Stimulation 
of  the  sympathetic  origins  gives  rise  more  esjDecially  to  vascular  constriction, 
and  only  secondarily  to  dilatation  (Fran9ois-Franck  and  Hallion).  The  pan- 
creas receives  its  secretory  nerves  from  the  vagus  (Pawlow,  Morat).  Stimula- 
tion of  the  branches  of  the  sympathetic  simultaneously  with  that  of  the  vagus 
diminishes  and  arrests  the  effects  of  the  latter,  by  means  of  a  mechanism  which 
is  probably  one  of  inhibition  (Morat). 

The  liver  receives  its  nerves  from  the  great  sympathetic,  from  the  same  region 
of  the  spinal  cord,  extending  from  the  sixth  thoracic  to  the  second  lumbar.  This 
result  has  been  ai'rived  at  by  observing  the  vaso-constrictor  effects  caused  by 
stimulation  of  the  origins  of  these  nerves  in  the  conununicating  branches.  By 
directly  stimulating  the  nerves  of  the  liver  or  the  large  trunks  (splanchnic)  which 
furnish  them,  its  circulation  and  its  proper  function  are  both  simultaneously 
acted  on  ;  the  excretion  is  modified,  if  not  the  biliary  secretion.  The  large 
splanchnics  are  the  motor  nerves  of  the  biliary  ducts.  An  inhibitory  apparatus 
co-exists,  which  can  only  be  brought  into  play  experimentally  by  reflex  stimula- 
tion acting  on  its  central  end.  Stimulation  of  the  central  end  of  the  vagus 
generally  provokes  dilatation  of  the  sphincter  choledochus  in  a  manner  parallel 
to  the  contraction  of  the  gall  bladder  (Doyon). 

Stunulation  of  the  splanchnics  obviously  acts  on  the  glycogenic  function  of 
tlie  liver,  which  is  excited  by  it.  An  increased  activity  in  the  transfoi*mation  of 
glycogen  into  glucose  has  been  observed  ;  this  action  apjiears  to  be  independent 
of  the  state  of  the  circvilation  ;  it  would  tend  to  prove  the  existence  of  strictly 
secretory  or  glucose-forming  nerves  (Morat  and  Dufoui't). 

The  spleen  receives,  by  the  splanchnic,  nerves  coming  to  it  from  the  spinal  cord, 
from  the  third  or  fourth  dorsal  as  far  as  the  first  lumbar  (Schaffer  and 
Moore). 

The  colon  receives  filaments  of  distribvition  from  the  mesenteric  nerves  arising 
from  the  first  lumbar  pair,  almost  up  to  the  sixth. 

The  rectum  and  the  anus  receive  elements  of  similar  origin  which,  descending 
by  the  mesenteric  nerves, rejoin  the  hypogastric  plexus,  where  they  are  duplicated 
by  those  provided  by  the  second  and  third  sacral  pairs.  The  anus  also  receives 
filaments  of  sacral  production,  which  reach  it  directly  by  the  hsemorrhoidal  or 
anal  nerve. 

Innervation  of  the  urinary  apparatus. — The  kidney  (chiefly  by  the  small 
splanclmic  nerves)  receives  nerves  from  the  great  syinpathetic,  some  vaso-motor, 
others  jDrobablj^  exerting  a  directly  stimulating  action  on  secretion.  The  vaso- 
motor effects  induced  by  stimulation  of  these  nerves  can  be  readily  demonstrated. 
They  take  origin  more  especially  from  the  twelfth  and  tliirteenth  thoracic  roots 
Bradford). 

The  innervation  of  the  bladder  is  almost  the  same  as  that  of  the  rectxim.  Like 
the  latter,  it  receives  filaments  from  the  hypogastric  plexus,  which  itself  derives 
them  from  a  double  source,  hunbar  and  sacral.  The  nerves  of  the  fundus  and 
of  the  neck  of  the  bladder  are  antagonistic  to  one  another,  being  motor  for  the 
one  and  inhibitory  for  the  other  ;  their  separation  at  their  bulbar  and  sacral 
origins  is  in  no  sense  absolute. 

Innervation  of  the  genital  apparatus. — The  genital  ajoparatas  is  composed  of 
reservoirs  (in  the  male  vesical se  seminales,  in  the  female  the  utertis)  and  of  erec- 


CONSCIOUS  AND  UNCONSCIOUS:  THEIR  SEPARATION  347 


tile  organs  (corpora  cavernosa,  clitoris).     The  first  are  motor  and   the  second 
vascular  structxu'es.     Both  are  lined  with  secretory  organs. 

Tiirgescence  of  the  erectile  structures  is  induced  by  stimulation  of  the  erector 
nerves  of  Ecldiard  (second  and  third  sacral  pair),  their  flaccidity  by  that  of  the 
mesenteric  nerves.  But  these  latter  also  contain  dilator  elements  (FranQois- 
Franck)  and,  conversely,  some  at  least  of  the  sacral  roots  (the  second)  contain 
constrictor  elements  (Nicolsky).  The  internal  pudic  nerve  also  contains  ele- 
ments belonging  to  both  of  these  orders  (Fran§ois-Franck). 

Contraction  of  the  vesiculce  seminales  with  expulsion  of  their  contents  is  pro- 
voked by  stimulation  of  the  mesenteric 
nerves  (Loeb,  Reiny).  The  contractions  of 
the  uterus  are  vmder  the  control  of  the  same 
nerves.  The  special  action  of  the  sacral 
nerves  upon  these  organs  is  unknown. 
Stimulation  of  the  lumbar  sympathetic  gives 
rise  to  simultaneous  contraction  of  the 
uterine  vessels. 

C.     TRANSMISSION    AND    CENTRALIZA- 
TION OF  IMPULSES— THE  MEDULLA 
OBLONGATA 

The  medulla  oblongata  is,  as  its  name 
implies,  a  prolongation  of  the  spinal 
cord  in  the  encephalic  cavity.  The 
fundamental  constituent  elements  of 
the  spinal  cord  may  here  also  be  ob- 
served, with  their  primary  arrangement 
still  very  obvious  ;  but  very  important 
changes  have  also  occurred,  and  new 
formations  have  been  superadded. 

Delimitation. — The  spinal  cord  only 
derives  its  external  stimuli  from  the 
organs  of  touch.  The  medulla  ob- 
longata,  in  addition  to  that  of  touch, 
enters  into  relation  with  other  senses, 
and,  if  we  were  not  bound  down  by 
morphologieal  definitions,  we  should 
comprehend  under  this  expression  of 
"  prolonged  spinal  cord  "  all  formations 
of  grey  matter  where  the  peripheral  neurons  of  the  sensorial  paths 
come  to  a  direct  termination.  In  any  case,  we  may  conventionally 
associate  with  it  those  grey  areas  from  which  the  sensori-motor  nerves 
arise  at  the  level  of  the  pons  and  of  the  aqueduct  of  Sylvius,  as  being 
an  obvious  prolongation  of  the  grey  meduUary  axis. 

Proper  functions. — The  meduUa  oblongata  not  only  collects  impulses 
provided  by  the  organs  of  the  senses,  but,  by  means  of  new  connexions 


Fig.  144. — Innervation  of  the  kidney 
and   of   the   bladder. 

K,  kidney  ;  B,  bladder  ;  Dxiii, 
thirteenth  dorsal  root  (in  the  dog)  ;  S^, 
first  sacral  ;  pn.g,  pneumogastric  ;  n.sp, 
splanclinic  nerves  (great  and  small)  ; 
gg.m.s,  superior  mesenteric  ganglion ; 
gg.hyp,  hypogastric  ganglion  or 
plexus  ;  n.er,  erector  nerve. 


348  SYSTEMATIC    FUNCTIONS 

and  formations,  it  elaborates  and  transforms  these  impulses  whatever 
be  their  origin,  in  order  to  adapt  them  to  aggregations  of  functions 
more  complex  than  those  of  the  spinal  cord  properly  so  called.  From 
this  point  of  view  the  medulla  oblongata  acquires  a  hierarchical  superi- 
ority over  the  last-named,  of  the  same  nature  as  that  possessed  by 
the  brain  over  it,  as  well  as  over  the  spinal  cord. 

Two  orders  of  centres. — The  medulla  oblongata,  as  from  the  physiological 
point  of  view  we  must  conceive  it  to  be,  and  so  as  not  to  describe  it  exclusively 
from  an  anatomical  asjaect,  but  also  from  a  functional  one,  will  then  comprehend 
two  modalities  of  grey  matter,  namely  :  the  first,  which  purely  and  simply 
continues  what  are  called  the  nuclei  of  origin  of  the  peripheral  nerves,  and  the 
second,  which  is  without  any  direct  relationship  with  these  origins  themselves, 
but  which  inaugurates  these  superposed  si/stems  which  are  here  progressively 
developed;  at  the  base  of  the  brain  in  its  ganglia,  behind  it  in  tlie  cerebellum,  at 
its  convexit}^  in  the  cortex. 

Motor  and  sensory  nuclei.— The  motor  nuclei  are  genviine  grey  nuclei,  in  Vvhich 
are  situated  the  origins  of  the  efferent  neurons,  in  every  way  resembling  those  of 
the  anterior  spinal  roots,  and  which  receive  their  proportional  jDart  of  the  cerebral 
neurons,  which  descend  from  the  cortex  to  distribute  its  specific  excitation  to 
them.  The  sensory  bulbar  nuclei,  if  it  be  wished  to  assimilate  them  anatomically 
to  the  motor  nuclei,  are  really  constituted  by  the  ganglia  of  origin  of  the  tri- 
geminal (or  of  Gasser),  of  the  vagus  (or  jugular),  of  the  glosso-pharyngeal  (or  of 
Andersh),  etc.,  which  continue  the  series  of  the  spinal  ganglia  of  the  posterior 
roots.  But  the  point  of  view  of  development  is  here  the  secondary  one,  and 
that  of  the  transmission  of  impulses  is,  on  the  contrary,  essential.  But  from 
this  latter  point  of  view  the  sensory  nuclei  of  the  medulla  oblongata  are  grey 
masses  receiving  the  terminations  (emissive  or  transmissive  poles)  of  the 
afferent  neurons  coming  from  the  periphery,  and  which  on  their  part  send  a 
proportional  number  of  fibres  of  projection  to  the  cortex  by  the  fillet  {ruhan  de 
Reil),  which  they  help  to  enlarge.  These  sensory  nuclei  repeat  the  arrangements 
of  those  of  the  spinal  cord.  As  regards  the  same  root,  and  even  as  regards  the 
same  fibre  of  each  root,  they  are  multiple  ;  for  these  roots  and  fibres  bifurcate 
into  ascending  and  descending  branches,  and  one  fibre  of  (for  example)  the  tri- 
geminal thus  bifurcated  will  seek  in  the  grey  medullary  substance  (or  even  lower) 
localities  analogous  to  the  cohimn  of  Clark,  to  the  grey  peri-ependymal  svibstance, 
and  to  the  nuclei  of  Goll  and  of  Burdach.  We  may  even  remark  concerning 
these  two  latter  nuclei,  that,  though  included  in  the  conventional  limits  of  the 
medulla  oblongata,  they  really  belong  to  the  spinal  cord,  as  they  are  in  direct 
relationship  with  its  special  roots. 

Grey  reticulated  bulbo-pontine  substance. — The  superadded  grey  masses 
belong  especially  to  the  reticulated  bulbar  and  pontine  substance.  Though 
often  diffuse,  they  are  occasionally  concentrated  into  distinct  nuclei  like  the 
nuclei  of  Roller,  in  whicli  it  is  supposed  are  represented  the  respirator }i  centre,  the 
vaso-motor  centre,  and  the  nucleus  of  the  tegmentum  (calotte).  These  grey  masses, 
which  are  no  longer  the  direct  origins  of  motor  nerves,  nor  receptive  of  the  direct 
extremities  of  the  sensory  nerves,  are  nevertheless  united  to  these  nerves,  since 
they  govern  them  ;  and,  ftirther,  they  are  not  without  relationship  with  the 
brain,  which  under  certain  circumstances  has  power  over  them. 

Their  functions  are  especially  reflex.  The  associations  between  sensory  and 
motor  nerves  effected  in  the  spinal  cord  are  mere  rough  sketches  when  compared 
with  those  of  the  medulla  oblongata  ;    the  former  necessarily  remain  local  and 


CONSCIOUS  AND  UNCONSCIOUS:  THEIR  SEPARATION  349 


give  rise  to  movements  which  are  also  limited,  and  often  without  much  functional 
significance,  at  least  in  the  superior  animals.  On  the  contrary,  the  sensory 
impulses  whicli  attain  the  medulla  oblongata  find  there  much  more  favourable 
conditions  of  reflective  association,  this  being  displayed  by  more  powerful  move- 
ments, some,  indeed,  revealing  a  gi-eat  tendency  to  generalization.  ^ 
Analytical  study  ;  Division. — The  analytical  study  of  the  medulla  oblongata 
from  a  functional  point  of  view  comprehends  then  the  functions  of  its  white 
tracts,  which  are  more  especially  conductors  of  the  second  order,  participating 
in  the  conscious  voluntary  functions  (those  of  the  first  order,  wliich  are  none 
other  than  the  cranial  nerves,  have  been  previously  studied)  ;  also  the  already 
specialized  reflex  functions, 
which  find  here  the  conditions 
necessary  to  their  existence. 
On  account  of  the  proximity 
of  the  centres  of  origin  of  the 
bulbar  nerves  to  the  reflex 
centres  belonging  to  the 
medulla  oblongata  itself,  it  is 
not  always  easy  to  decide 
whether  a  given  reflex  act 
results  from  a  simple  associa- 
tion on  the  spot  between  the 
nuclei  of  origin  of  the  bulbar 
nerves,  or  whether  it  is  caused 
by  the  participation  of  a 
superadded  centre.  But  tliis 
difficulty  is  not  peculiar  to 
the  medulla  oblongata  ;  the 
spinal  cord  also  presents  it, 
as  its  grey  matter  encloses 
elements  of  association  mixed 
with  its  exogenous  elements. 
It  is  these  which,  assuming 
in  the  medulla  oblongata  an 
importance  they  did  not  pos- 
sess in  the  spinal  cord,  bestow 
upon  it  its  sjjecial  functional 
significancf^. 


Corp.  giiad. 


Red  nuc. 


Locus  niger 


iOcus  ccerul. 


Subs.  cin. 


Pontine 


Arcijor 


Trap.  nuc. 


Eetic.  form. 


Speech 


Fig 


145. — So-called  ganglionic  grey  matter  of  the 
cerebral  trunk  (after  Charpy). 

Grey  masses  superadded  to  the  sensori-motor  nuclei. 


1.    Sensibility  and  Motricity  in  the  Medulla  Oblongata 

A.  Motor  paths  ;  anterior  pyramid. — At  the  inferior  portion  of 
the  medulla  oblongata  the  anterior  columns  (descending)  partially- 
cross  from  one  side  to  the  other,  on  the  median  line.  This  decussation, 
which  is  here  made  tract  by  tract,  renders  visible  to  the  naked  eye  an 
arrangement  of  the  same  nature,  very  general  in  the  whole  extent  of 
the  encephalo-medullary  nervous  axis,  where  it  is  made,  fibre  by  fibre, 
and  hence  is  rendered  visible  only  by  histological  methods.  It  must 
be  remembered  that  the  decussation  of  the  pyramids  is  only  a  fraction 
of  their  total  crossing  (even  including  only  the  descending  fibres)  ; 


350  SYSTEMATIC    FUNCTIONS 

that  it  is  incomplete  at  the  level  of  the  medulla  oblongata  (direct  tract  ; 
crossed  tract)  ;  and  that  it  does  not  by  itself  explain  the  connexion 
which,  in  motor  paralyses,  unites  the  hemisphere  of  one  side  to  the 
muscles  of  the  opposite  side. 

Stimulation. — Longet,  Laborde,  and  more  recently  Wertheimer  and 
Lepage,  have  directly  stimulated  the  anterior  bulbar  pyramids  and 
have  seen  this  stimulus  produce  movements  in  the  muscles  of  the 
opposite  side.  If  these  tracts  are  cut,  stimulation  of  the  inferior  end 
has  the  same  result.  There  can  then  be  no  doubt  that  the  anterior 
bulbar  pyra^nid  possesses  a  tnotor  function  which  at  first  sight  appears 
to  be  conferred  upon  it  by  its  continuity  with  the  motor  tracts  of  the 
corona  radiata  and  those  of  the  spinal  cord,  as  also  by  its  connexions 
(by  the  aid  of  these  tracts)  with  the  motor  area  of  the  cortex  on  one 
hand,  and  with  the  anterior  horns  of  the  spinal  cord  on  the  other.  The 
counterproof  of  this  may  be  effected  by  cutting  all  the  bulbar  tracts, 
except  the  pyramids  ;  it  is  found  that  in  this  case  stimulation  of  the 
motor  cerebral  area  still  produces  movements  in  the  limbs  (Brown- 
Sequard). 

Section. — The  bulbar  pyramid  is  a  motor  path  descending  from  the 
cortex  to  the  spinal  cord,  but  it  is  not  the  only  one,  as  is  proved  by  the 
following  experiments,  which  in  their  turn  serve  as  the  counterpart  of 
the  preceding  ones.  If  the  two  anterior  bulbar  pyramids  be  cut,  the 
animal  will  not  have  lost  all  power  of  movement  of  its  limbs.  At 
first  the  movements  may  be  disturbed  and  more  or  less  hindered,  but 
after  a  certain  time,  they  become  normal,  and  to  such  an  extent  that 
it  becomes  difficult  to  notice  any  alteration  depending  on  this  suppres- 
sion (Langley  and  Griinbaum,  Herzen  and  Loewenthal).  In  an  animal 
which  has  undergone  this  section,  stimulation  of  the  motor  area  still 
produces  localized  movements  in  the  limbs,  though  less  marked 
(Unverricht). 

Thus,  whether  by  section  around  it,  we  oblige  the  descending  impulse  to  pass 
through  the  pyramid,  or  whether,  by  section  of  the  latter  itself,  we  prevent  it 
from  thus  passing  there,  the  impulse  finds  a  passage  in  the  bulbar  paths.  We 
are  not  authorized  to  say  that  these  paths  are  rigorously  equivalent,  and  it  is 
improbable  that  they  are  so.  If  they  appear  to  us  as  being  sucli,  it  is  no  doubt 
because  we  do  not  know  how  to  distinguish  the  differences  characterizing  the 
functions  subsisting  in  each  case.  We  may  in  any  event  admit  that  after  tlie 
suppression  of  the  one  there  is  a  re-education  of  the^^nervous  system  and  a  tendency 
to  substitute  one  for  the  other  ;  a  substitution,  a  re-education  which  are  indicated 
by  the  time  which  must  elapse  before  the  more  or  less  complete  re-establishment 
of  the  function. 

Decussation. — The  bulbar  pyramid  is  only  partially  crossed  (bundle 
by  bundle)  with  that  of  the  opposite  side,  at  the  conventional  limit  of 
the  spinal  cord  and  of  the  medulla  oblongata.     The  crossed  part  pene- 


CONSCIOUS  AND  UNCONSCIOUS :  THEIR  SEPARATION    351 


-  Pyr.  t. 


Meynert's  bundle 


('ran.  fibres 


trates  into  the  lateral  column  of  the  spinal  cord  on  the  opposite  side  ; 
the  direct  path  remains  on  the  same  side  (direct  pyramidal  tract,  or 
tract  of  Tiirck),  and  penetrates  into  the  anterior  column  of  the  spinal 
cord  on  the  same  side.  It  is  very  generally  maintained  that  the  direct 
tract  decussates,  in  its  turn,  fibre  by  fibre,  in  the  spinal  cord,  by  its 
commissures  ;  but  neither  anatomy  nor  physiology  gives  a  decisive 
proof  either  for 
or  against  this 
decussation.  The 
most  probable  ex- 
planation seems  to 
be  that  it  is  not 
total,  but  that  the 
impulse  descend- 
ing from  one  of  the 
halves  of  the  brain 
remains  partially 
in  the  correspond- 
ing half  of  the 
spinal  cord  and 
goes  partially  to 
the  muscles  of  the 
opposite  side.  In 
this  respect  a  uni- 
vocal  and  absolute 
formula  would 
be  incorrect ;  for 
both  from  a  phys- 
iological and  clini- 
cal point  of  view 
it  has  been  found 
that  certain  movements  are  bilateral,  and  others  unilateral,  according 
to  the  necessities  of  the  function  ;  finally,  other  movements  may  be 
also  crossed  according  to  the  circumstances  with  which  they  are 
associated,  bilateral  in  certain  cases,  unilateral  in  others. 

The  question  of  unilaterality  or  bilaterality  has  been  raised  as  regards  the 
crossed  as  well  as  the  direct  pyramidal  tract.  Pitres  and  Dignat,  Dejerine  and 
Thomas,  have  frequently  noticed  that,  in  addition  to  the  direct  tract  which 
follows  the  anterior  cokuim,  there  is  another  direct  tract  following  the  lateral 
cokimn  on  the  same  side.  Further,  decussation  of  the  pyramids  may,  as  these 
autliors  have  noticed,  present  a  gi^eat  number  of  variations,  even  to  the  point  of 
being  sometimes  entirely  wanting.  In  animals,  the  direct  pyramidal  tract  as 
it  exists  in  man  (tract  of  Tiii'ck,  going  to  the  anterior  spinal  column  of  the  same 


Pyr.  deous.i. 


T.  of  Tiirck 


Fig.    14fi. — Tlie  pjTamidal  tract  (after  Charpy). 

The   geniciilated   or    cranial   tract,   and   the   tract  of  Tiirck   are 
decussated  fibre  by  fibre. 


352  SYSTEMATIC    FUNCTIONS 

ftkle)  is  lacking  ;  it  is  replaced  by  a  direct  tract  going  to  the  lateral  column  of 
the  same  side,  consequently  similar  to  that  pointed  out  in  man  by  Pitres  and 
Dignat,  and  which,  in  all  probability,  functionally  replaces  it. 

A  longitudinal  section  effected  in  the  anterior  furrow  of  the  medulla  oblongata, 
consequently  cutting  the  decussation,  produces  a  certain  degree  of  paresis, 
that  is  to  say,  enfeeblement  of  the  four  extremities,  but  without  entirely  paralys- 
ing them :  this  affects  the  side  opposite  to  the  hemisection.  A  hemisection  of 
the  bulb  above  the  decussation  will  also  produce  a  weakening  of  the  four  ex- 
tremities, but  without  paralysing  thein  entirely  ;  the  weakness  affects  the  side 
opposite  to  the  hemisection.  These  two  resiilts  support  the  view  that  there  is  a 
mixture  in  each  half  of  the  bulb  of  fibres  destined  for  the  two  halves  of  the  body 
and  generally  in  unequal  proportions. 

So  far,  no  distinct  functional  attribution  for  the  crossed  and  the  direct  tract 
has  been  discovered.  This  last  tract  does  not  extend  beyond  the  inferior  limit 
of  the  dorsal  region,  which  indeed  it  scarcely  reaches.  None  of  them  takes  part 
in  attaching  it  to  the  innervation  of  the  muscles  of  the  trunk.  As,  in  animals, 
the  two  tracts  are  confounded  in  the  lateral  cohmm,  isolated  stimulation  of  these 
parts  is  im2:)ossible. 

Alternate  hemiplegia. — Giibler  was  the  first  to  draw  attention  to  a  forjn  of 
hemiplegia  which  attacks  the  face  on  one  side  (that  corresponding  to  the  lesion) 
and  the  limbs  on  the  opposite  side,  and  which  is  caused  by  a  lesion  limited  to 
half  of  the  medulla  oblongata  or  of  the  p»ons  above  the  decussation.  A  lesion 
thus  situated  attacks  simultaneoiisly  the  peripheral  neurons  of  the  facial  of  the 
corresponding  side  (consequently  not  decussated)  and  the  deei?  neurons  of  the 
muscles  of  the  limbs,  which  deciissate  a  little  lower  down. 


B.  Sensory  paths  ;  fillet  (rub an  de  Reil). — At  the  back  and  a 
little  above  the  decussation  of  the  anterior  pyramids  (therefore  in  the 
thickness  of  the  bulb  itself)  another  decussation  will  be  found,  which 
is  effected  by  the  sensory  paths,  and  which  closely  repeats  the  preceding 
one.  The  crossed  sensory  tract  (consequently  ascending)  commences 
in  the  nuclei  of  Goll  and  of  Burdach  and  ascends  to  the  cortex,  with  or 
without  interruption  (and  this  is  the  point  under  discussion)  in  the 
optic  thalamus.  This  crossed  sensory  tract  is  duplicated  laterally  by 
a  direct  tract  arising  from  the  grey  medullary  substance,  and  these  two 
tracts  united  form  the  fillet  {ruban  de  Reil).  This  tract  is  again  slightly 
enlarged  in  the  medulla  oblongata,  by  the  addition  of  fresh  sensory 
paths  (also  crossed)  proceeding  from  the  nuclei  of  the  trigeminal,  the 
glosso-pharyngeal  and  the  vagus,  and  also  by  that  of  sensorial  paths 
proceeding  from  the  glosso-pharyngeal  (taste)  and  from  the  acoustic 
(audition). 

Clinical  experience  has  collected  a  certain  number  of  observations 
which  tend  to  prove  that  hemianaesthesia  (of  the  opposite  side)  is  the 
consequence  of  the  interruption  of  the  fillet  (or  ruban  de  Reil)  ;  but 
insensibility  has  also  been  observed  to  result  from  bulbar  lesions  other 
than  those  of  the  fillet.  There  is  then  for  the  sensory,  as  also  for  the 
motor  paths,  a  certain  amount  of  uncertainty  as  to  the  functional  part 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    353 

played  by  these  different  conductors,  or,  in  other  words,  concerning 
the  conditions  proper  to  each  tract  in  the  exercise  of  sensory  functions. 

Alternate  hemianaesthesia. — Alternate  hemiansesthesia  has  been  described  of 
which  the  mechanism  is  functionally  similar  to  tliat  of  the  hemiplegias  of  this 
natiire.     A  lesion  localized  in  one  of  the  halves  of  the  organ  would  affect  smiul- 


Fillet  (rul)uii  r/e 
lieil) 
{sensory  t.) 


Corp.  quad. 


Lat.  Filfet. 
{acoustic  t.) 


Cochl.  n. 

Sensor,  cran.  nuleas. 


X.  of  Goll. 

y.  of  Biird. 
Ani.  lat.  t. 

Post.  col. 


Fig.    147. — The  fillet  {ruban  de  Reil)  or  scnsorj'  tract  (after  Charpy). 

The  central  acoustic  iJath  (acoustic  tract,  lateral  fillet,  ruban    de   Reil)   is   indicated   in   red. 
Diagram. 


taneously  the  peripheral  neurons  (not  decussated)  of  the  trigeminal  and  the  deep 
neui'ons  (decussated),  corresponding  to  the  sensory  nerves  of  the  limbs. 

Physiological  experiment  reproduces  tliis  form  of  hemiansesthesia  by  hemi- 
section  of  the  bulb.  It  is  possible  to  verify,  as  the  result  of  this  operation,  a 
diminution  of  sensation  in  the  half  of  the  body  of  the  opposite  side,  and  a  hyper- 
sesthesia  of  the  corresponding  side,  as  Brown-Sequard  has  pointed  out  in  hemi- 
section  of  the  spinal  cord ;  anassthesia  of  the  surface  of  the  same  side,  as  Magendie 
has  observed  ;   and  finally  those  trophic  disturbances  of  the  ball  of  the  eye  which 

P.  A  A 


354  SYSTEMATIC    FUNCTIONS 

usvially  accompany  section  of  the  trigeminal,  and  also  follow  section  of  its  roots 
as  Duval  and  Laborde  have  verified. 

Expression  of  the  emotions. — The  movements  of  the  face,  due  to  the 
contraction  of  its  cutaneous  muscles  which  are  supphed  by  the  facial, 
are  called  expressive,  because  they  markedly  take  part  in  the  expression 
of  genuine  or  feigned  emotions  and  passions. 

2.  Local  Reflexes 
The  fillet  {ruban  de  Reil)  and  the  anterior  pyramid  are  paths  apper- 
taining, the  first  to  conscious  sensibility,  and  the  second  to  voluntary 
movement.     They  are  both  connecting  paths,  extended  in  two  different 
directions,  between  the  cerebral  cortex  and  the  grey  matter  of  the 
spinal  cord  and  medulla  oblongata.     Their  suppression  prevents,  or 
at  least  in  a  certain  degree  disturbs,  the  manifestations  of  consciousness 
and  of  the  will.     The  medulla  oblongata  contains  other  associations 
which  can  dispense  with  the  cortex,  and,  isolated  from  it,  suffice  for 
the  regulation  of  certain  functions  of  a  reflex  order.     These  connexions 
are  effected  in  its  grey  matter  ;    they  are  of  two  orders.     The  first 
simply  unite  between  themselves  the  motor  origins  and  the  sensory 
terminations  of  the  bulbar  nerves  for  the  performance  of  simple  reflexes  : 
they  may  be  called  immediate  centres,  or  those  of  the  first  degree.     The 
second  are  associations  superposed  to  the  grey  nuclei    of    subjacent 
origin  (medullary  and  bulbar)  and  which  are  mediate  cejitres,  or  those 
of  the  second  degree.     This  co-existence  of  centres  belonging  to  two 
different  orders  in  regions  in  the  immediate  vicinity  of  the  grey  matter 
is  due  to  the  fact  of  the  medulla  oblongata  containing,  as  has  already 
been  mentioned,  both  the  continuation  of  the  column  of  origin  of  the 
peripheral  nerves  and  fresh  superadded  formations,  which  are  no  longer 
original  centres  like  those  of  the  spinal  cord.     These  formations  have 
already,  in  some  degree,  acquired  the  power  of  autonomy,  so  highly 
developed  in  the  brain  ;   only  they  exercise  it  no  longer  in  the  manner 
of  an  action  varied  and  contingent,  as  does  the  brain  ;    but,  on  the 
contrary,  in  a  regular  and  periodic  fashion,  whence  the  name  of  auto- 
matic centres  sometimes  applied  to  them. 

As  regards  the  internal  fiuictions  ensiu'ing  nutrition  (respiration,  circulation, 
excretion,  etc.)  the  impulse  is  automatically  renewed  in  organs  placed  in  closed 
chains.  In  the  external  functions  which  maintain  our  relations  with  other  living 
beings,  the  renewal  of  impulse  becomes  in  a  manner  fortuitous.  Here  the  cycles 
present  the  appearance  of  a  chain  open  to  the  exterior.  The  medulla  oblongata 
is  a  rough  sketch  of  these  systems  of  relation  by  the  help  of  which  the  animal 
expresses  what  it  has  felt  by  a  defensive  motor  or  even  conventional  manifesta- 
tion. A  cry  is  a  ixianifestation  of  this  natvire  ;  there  is  a  reflex  cry  of  purely 
bulbar  origin. 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    355 

1.  Reflex  cry. — In  an  animal  which  has  undergone  supra-bulbar 
section  of  the  encephalon,  stimulation  of  the  sensory  nerves  produces 
a  short  unmodulated  cry,  which  has  been  compared  by  Vulpian  to 
that  elicited  by  pressure  on  dolls  made  as  playthings  for  children. 
This  cry  is  obviously  of  reflex  origin,  and  has  some  analogy  to  the  cry 
which  is  known  as  rneningitic. 

The  cry,  like  phonation,  is  an  adaptation  of  the  respiratory  appara- 
tus (essentially  of  internal  function)  to  an  external  function,  by  an 
alteration  in  the  connexions  uniting  its  elements  between  themselves 
and  with  the  neighbouring  elements  ;  the  system  of  respiratory  nerves 
becomes  that  of  nerves  of  phonation,  or,  according  to  the  usual  ex- 
pression, the  respiratory  centre  becomes  that  of  phonation. 

The  cry  is  the  rough  sketch  of  phonation,  of  language  such  as  it 
exists  in  us.  For  the  production  of  articulated  speech  a  nervous  stimu- 
lus is  required,  into  which  the  medulla  oblongata  enters  as  a  component 
part,  and  one  which  is  superposed  to  a  definite  region  of  the  cerebral 
cortex.  In  this  extension  of  the  cycle  the  cerebral  cortex  does  not 
purely  and  simply  take  the  place  of  the  bulbar  centre,  but  utilizes  the 
relatively  simple  organization  of  the  latter  for  the  performance  of  a 
more  complex  act. 

2.  Winking  of  the  eyelids. — The  medulla  oblongata  controls  sensi- 
bility and  movement  of  the  face,  the  first  by  means  of  the  trigeminal, 
the  second  by  that  of  the  facial.  These  nerves  are  connected  in  the 
medulla  oblongata  for  the  performance  of  defensive  reflexes,  of  which 
the  winking  of  the  eyelids,  to  cause  removal  of  tears,  furnishes  an 
example.  This  movement  is  a  correlated  one,  the  two  eyelids  being 
lowered  and  raised  together  at  the  same  moment.  This  correlation 
is  due  to  a  partial  decussation,  or  to  elements  of  association  which  cause 
the  stimulation  (reflex)  reaching  the  nucleus  of  one  side,  to  be  trans- 
mitted to  that  of  the  opposite  side.  If  an  antero-posterior  section 
between  the  nuclei  of  the  two  nerves  is  made  exactly  in  the  median 
line,  this  correlation  ceases  ;  winking  of  the  eyelids  can  then  be  per- 
formed independently  either  on  the  right  or  the  left  side  (Vulpian). 

From  this  experiment  may  be  deduced  the  physiological  proof  that 
the  decussation  of  fibres  belonging  to  the  facial,  if  it  exists,  is  not  com- 
plete, for,  if  it  were  so,  the  median  section  would  bring  about  paralysis 
of  both  sides. 

3.  Conjugated  deviation  of  the  eyes. — Certain  functions  require  a 
succession  of  muscular  efforts  for  the  attainment  of  the  end  in  view 
(the  peristaltic  movement  of  the  digestive  tube,  movement  of  the  hmbs 
in  walking).  Others  demand  fixity  and  parallelism  of  these  efforts  ; 
such  is  that  of  binocular  vision  when  the  conditions  as  regards  the 


35(> 


SYSTEMATIC    FUNCTIONS 


formation  of  retinal  images  and  of  the  superposition  of  two  images  are 
assumed  to  be  normal.  The  association  of  the  two  eyeballs,  which 
strictly  solidarizes  their  movements,  is  attributed  to  anatomical  arrange- 
ments, themselves  consequently  of  a  fixed  order.  These  arrangements, 
which  allow  of  some  variation  according  to  the  authors  who  have 
described  them,  are  all  based  on  general  principles,  namely  :  that  a 
motor  stimulus,  reaching  the  abductor  muscle  of  the  eye  on  one  side 
must  of  necessity  affect  at  the  same  time  and  to  the  same  degree  of 
intensity  an  adductor  muscle  of  the  eye  of  the  opposite  side,  and 
reciprocally. 

Duval  and  Laborde  maintain  that  the  nucleus  of  the  abducens,  or  sixth  nerve, 
supplying  the  right  external  rectus,  also  contains  the  origins  of  the  branch  to 
the  internal  rectus  of  the  opposite  eye  ;  in  reality,  this  aberrant  branch  arises 
from  the  nucleus  of  the  sixth  nerve,  follows  the  posterior  longitudinal  bundle, 
decussates  with  its  homologue  below  the  corpus  quadrigeminura,  and,  contained 
in  the  trunk  of  the  abducens  (sixth  nerve)  of  the  opposite  side,  is  detached  to  go 
to  the  right  internal  rectus  muscle.  The  impulse  leaving  the  brain  would  only 
have  to  be  directed  to  the  nucleus  of  the  sixth  nerve  to  cause  the  eyes  to  be 
deviated  in  any  given  direction.  Others  consider  (Spitzka)  that  the  branch  of 
the  internal  rectus  also  decussates  in  the  median  luie,  but  its  own  nucleus  does 
not  form  a  part  of  the  nucleus  of  the  sixth  nerve,  but  of  that  of  the  oculo-motor 
nerve.  According  to  this  hypothesis,  an  impulse  coming  from  the  brain  is  simul- 
taneously directed  to  the  nucleus  of  the  sixth  nerve  and  to  the  fraction  of  the 
nucleus  of  the  oculo-motor  nerve  containing  the  origin  of  the  branch  of  the  oppo- 
site internal  rectus.  The  connexion  causing  the  co-operation  would  not  be 
effected  by  the  nucleus  receiving  the  impulse,  but  by  the  elements  bringing  it 
there.      Theoretically  the  solutions  of  this  problem  do  not  greatly  differ. 

rnier.  rectus.  Convergence     for 

adaptation  to  dis- 
tances.— In  reality 
the  visual  axes  of 
each  eye  are  not 
parallel,  but  con- 
verge on  the  object 
looked  at,  and  are 
the  more  con- 
vergent in  propor- 
tion as  the  object 
is  nearer.  The 
fixity  of  the  angle 
of  convergence  is 
then  not  constant, 
and  the  magnitude 
To  increase  this  value  it 


Exter.  red II 


Ociilo  '  motor  N. 


Ext.ocuJo-mot.  y 
{sirth  N.) 


Fit;.    148. — Co-operation    of    the    nuclei    of    origin    of    the 
sixth  and  third  nerves. 
The  partial  nucleus  of  the  internal  branch  of  the  third  nerve 
regarded  as  a  dependence  of  the  nucleus  of  the  sixth  nerve. 


of  this  angle   changes  with  the  distance 

is  necessary  for    the  contraction    of   the  internal   rectus    muscles  to 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    357 

slightly  surpass  that  of  the  external  rectus  muscles  ;  and  for  this  to  come 
about  the  impulse  must  be  distributed  in  slightly  predominating 
quantity  to  that  portion  of  the  nucleus  of  the  oculo-motor  nerve  which 
contains  the  origins  of  the  fibres  proceeding  to  the  internal  recti. 

Partial  nuclei. — Anatomically  the  nucleus  of  the  oculo-niotor  nerve  is  sub- 
divided into  a  series  of  partial  nuclei,  corresponding  to  its  different  branches, 
and  therefore  to  each  of  the  recti  or  obliqui  muscles,  in  addition  to  the  nuclei 
answering  to  the  internal  musculature  of  the  eye.  These  last  are  situated  nearer 
to  the  median  line,  and  rather  in  the  superior  portion  of  the  origins  of  the  third 
nerve  ;  the  others  are  outside  and  prolonged  lower  down.  These  facts  have 
been  verified  by  effecting  the  isolated  ablation  of  the  peripheral  muscles  and 
observing,  by  means  of  the  method  of  Nissl,  the  chromatolytic  alterations  of 
the  cells  of  origin. 

Functional  dissociation. — By  localized  stimulation  of  each  of  these  partial 
nuclei,  experimental  determinations  have  been  made  which  nearly  correspond 
with  those  effected  by  anatomical  means  (Hensen  and  Volkers). 

4.  Sympathetic  origins. — The  nuclei  of  the  recti  and  obliqui  muscles 
are  the  continuation  of  the  direct  motor  origins  of  the  nerves  of  the 
life  of  relation,  which  terminate  at  this  level. 

The  nuclei  of  the  internal  muscles  of  the  eye  (ciliary  muscle  of  accom- 
modation and  sphincter  muscle  of  the  iris)  are  not  the  equivalent  of 
the  preceding. 

The  fibres  arising  from  them  do  not  go  directly  to  the  deep  muscles 
of  the  eye,  but  are  fibres  of  projection  of  the  second  order,  which  stop 
in  the  ganglia  and  the  ciliary  plexus.  These  fibres  contain  the  spinal 
origins  of  the  great  sympathetic,  to  which  they  belong,  and  of  which 
they  also  mark  the  highest  point  of  emergence  in  the  grey  axis. 

Apparatus  of  association  ;  posterior  longitudinal  bundle. — The  grey  bulbar 
matter  acts  as  an  associating  agent  with  regard  to  a  large  number  of  motor  nerves, 
spinal  as  well  as  bulbar,  for  the  performance  of  a  certain  number  of  definite 
ftmctions.  The  impulses  conveyed  to  it,  not  only  by  the  nerves  of  touch,  but 
also  by  those  of  the  superior  senses,  are  here  reflected  to  the  motor  nviclei  of  the 
eyes  and  of  the  trunk  by  a  special  apparatus  of  association,  the  posterior  longi- 
tudinal bundle  or  posterior  longitudinal  tract.  This  structure  is  situated  on  each 
side  of  the  median  furrow,  below  the  floor  of  the  fourth  ventricle  and  of  the 
aqueduct  of  Sylvius  ;  it  is  the  continuation,  and  the  equivalent,  but  in  a  more 
differentiated  form,  of  the  antero-lateral  column  of  the  spinal  cord.  It  is  formed 
by  neurons  of  association,  which  receive  the  impulse  coming  from  the  sensory 
nevu-ons  by  one  of  their  poles,  and  by  the  other  transmit  it  to  the  motor  neurons. 
It  brings  into  relation  the  sensory  bulbar  nuclei  and  the  corpora  quadrigemina, 
more  especially  with  the  motor  nerves  of  the  eyes  and  of  the  trunk. 

5.  Deglutition. — At  the  entrance  of  the  digestive  paths  we  are  con- 
fronted by  an  act  which  forms  the  transition  between  those  of  the 
external  and  those  of  the  internal  functions  :  this  is  deglutition,  which 
commences  with  an  act  of  conscious  sensibility  and  voluntary  move- 


358 


SYSTEMATIC    FUNCTIONS 


Oculo-motor 


N.IkI. 


ment  and  is  completed  by  reflex  movements.  Once  again  it  is  the 
medulla  oblongata  which  is  the  locality  for  the  organization  of  the 
system  subserving  deglutition,  the  conducting  fibres,  both  sensory 
and  motor,  of  this  system  being  met  with  in  a  certain  number  of  bulbar 
nerves,  namely,  the  trigeminal  (mylo-hyoid  muscle),  the  facial,  the 
hypoglossal,  and  the  vago-spinal,  which  perform  the  function  of  motor 
nerves  connected  with  the  sensory  elements  contained  in  the  palatine 
nerves  (of  the  superior  maxillary),  the  superior  laryngeal  nerves,  and, 
lastly,  the  glosso-pharyngeal,  which  are  less  essential  than  the  preced- 
ing. The  point  of 
departure  is  the 
irritation  of  the 
bolus  of  food  occur- 
ring at  the  level  of 
the  isthmus,  on  the 
extremities  of  the 
palatine  nerves. 
The  laryngeal 
nerves  intervene  to 
defend  the  entrance 
of  the  respiratory 
paths. 

The  centre  of 
association  of  these 
different  nerves  is 
situated  bet  ween 
two  planes,  of  which 
the  superior  passes 
through  the  acous- 
tic tubercules,  and 
the  inferior  through 
the  apex  of  the 
calamus  ;  according 
t  o  Markwald,  a 
little  above  and 
outside  of  the  grey 
wing,  above  the  re- 
spiratory centre.  Sections  made  above  or  below  the  limits  just  pointed 
out  permit  of  the  persistence  of  swallowing  (life  being  maintained  by 
artificial  respiration).  The  succession  of  peristaltic  movements,  which 
continue  from  the  pharynx  to  the  oesophagus,  is  assured  by  a  regular 
transmission  of  impulses  passing  through  the  successive  nuclei  of  the 


Fig.    149. — Posterior  longitudinal  bvindle. 

iV. 6. Z,' special  nucleus  of  the  longitudinal  bundle;  P.cer,  crus 
cerebi  ;  T.quadr,  corpora  quadrigemina  ;  P.  pons. — III  to  XII, 
nuclei  of  origin  of  the  cranial  nerves,  bearing  the  number  corre- 
sponding to  the  usual  classification. 

The  grey  matter  of  the  spinal  cord  is  united  to  that  of  the 
Ijulbar  nuclei,  and  the  two  together  to  the  corpora  quadrigemina, 
})y  neurons  of  association  or  intercentral  nei.irons  whose  union  forms 
the  longitudinal  bundle.  These  neurons  have  different  directions, 
some  ascending  (in  black),  others  descending  (in  red). 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    35& 

motor  nerves  which  control  the  pharyngeal  and  oesophageal    con- 
strictors. 

6.  Mastication,  suction. — Like  the  preceding,  these  acts  are  of  reflex 
nature.  They  are  performed  after  the  removal  of  the  brain  in  young 
animals  when  an  appropriate  sensory  stimulus  is  applied  (Gads,  Brown- 
Sequard),  viz.  :  touching  of  the  anterior  portion  of  the  buccal  mucous 
membrane,  irritation  of  the  tactile  extremities  of  the  trigeminal.  The 
nerves  of  the  special  senses  do  not  intervene.  The  fifth  pair  is  associ- 
ated with  both  a  sensory  and  several  motor  nerves,  namely  :  motor 
branch  of  the  trigeminal  (mylo-hyoid  muscles,  anterior  belly  of  the 
digastric,  and  external  pterygoid),  facial  (muscle  of  the  lips  and  stylo- 
hyoid), hypoglossal  (muscles  of  the  tongue  and  sub-hyoidean  muscles). 
The  reflex  on  the  corresponding  side  is  suppressed  by  a  section  separat- 
ing the  sensory  nuclei  and  motor  nuclei  of  the  trigeminal. 

3.     General   reflexes 

The  sensori-motor  functions,  which  are  carried  out  by  the  connexions 
of  the  grey  bulbo-pontine  substance,  appertain  in  both  consciousness 
and  unconsciousness,  and  the  boundary  dividing  these  is  often  in- 
definite, or  but  little  marked.  We  may  form  a  conception  of  this  by 
the  help  of  some  significant  examples  of  both  kinds,  namely  :  as  regards 
the  first,  phenomena  of  sensation  and  of  locomotion  ;  as  concerns  the 
second,  regulating  action  on  the  functions  of  nutrition,  respiration, 
circulation,  secretion,  etc. 

1.  Common  sensorium. — The  substantia  reticularis  grisea  which,  at 
the  level  of  the  pons,  surmounts  and  continues  the  reticulated  substance 
which  is  properly  bulbar,  brings  about  the  sensori-motor  associations 
already  noticed  by  Lorry,  and  which,  according  to  Longet  and  Vulpian, 
give  it  the  value  of  a  coimnon  sensorium. 

In  a  mammal  from  which  the  cerebral  hemispheres,  the  optic 
thalami,  all  the  encephalon  with  the  exception  of  the,cerebellum,  the 
corpora  quadrigemina,  the  pons  and  the  bulb  have  been  removed, 
stimulatioruof  a  sensory  nerve  provokes  motor  reactions  of  an  obviously 
painful  character.  This  stimulation  arouses  prolonged  plaintive  cries, 
entirely  different  from  the  short,  in  a  sense  mechanical,  cry  of  the 
animal  deprived  of  the  pons  while  the  bulb  is  left  intact.  These  painful 
cries  are  accompanied  with  laboured  respiration  and  attempts  at  flight  ; 
all  these  being  reactions  which,  at  first  sight,  do  not  differ  from  those 
of  an  animal  retaining  the  brain.  Sensation  must  then  exist,  as  it  is 
manifested  by  those  characteristic  signs  by  which  we  are  accustomed 
to  recognize  it.  The  difference  in  this  case  is,  that  it  leaves  no  per- 
sisting trace  behind  it,  is  7iot  accompanied  by  ynemory,  but  disappears 

A  A 


360  SYSTEMATIC    FUNCTIONS 

with  the  7notor  reactions  ivhich  have  served  for  its  external  manifestation. 
From  the  fact  of  this  non-preservation  of  sensation,  the  phenomenon 
is  entirely  reflex,  but  is  at  the  same  time  painful  ;  that  is  to  say,  con- 
scious. The  phenomenon  is  a  transitional  one,  leading  to  the  effects 
resulting  from  the  intervention  of  the  brain,  in  which,  on  the  contrary, 
the  character  of  immediate  reflexion  disappears  more  or  less  completely 
in  proportion  as  the  phenomenon  of  conservation  of  sensation  or  of 
memory  becomes  more  marked.  In  this  simple  reflex,  where  the 
traces  of  sensation  are  unrecognizable,  the  phenomenon  is  excito-motor  ; 
in  the  reflex,  accompanied  with  sensation,  but  without  memory,  the 
phenomenon  is  sensitivo-motor  or  sensori-motor  ;  in  the  case  where 
reflex  succession  has  in  its  turn  become  unrecognizable,  by  the  inter- 
position of  cerebral  acts  of  intelligence,  the  phenomenon  is  ideo-motor 
(Carpenter). 

2.  Locomotive  functions. — A  function  which  also  imphes,  in  the 
motor  order,  associations  of  a  compHcated  nature,  is  locomotion  in 
vertebrata,  and  especially  in  mammals  ;  and,  combined  with  it,  is 
standing  in  the  upright  attitude.  As  Longet  has  shown,  the  pons 
plays  a  part,  not  certainly  exclusive,  but  essential,  in  this  function. 

Part  played  by  the  pons. — After  the  ablation  of  the  cerebral  hemi- 
spheres and  the  optic  thalami  in  a  rabbit,  if  the  pons  be  left  intact  the 
animal  will  be  seen  to  assume  the  ordinary  attitude  of  repose  ;  if  ex- 
cited, it  performs  some  regular  steps,  and  then  again  becomes  motion- 
less. It  will  even  sometimes  make  some  steps  without  apparent 
provocation,  no  doubt  incited  by  some  internal  stimulus.  //  the 
pons  is  destroyed,  all  locornotion  heco^nes  impossible,  and  the  animal 
can  no  longer  stand  upright  on  its  paws.  Experiments  of  the 
same  nature  on  animals  of  different  classes,  birds,  fish,  batrachia, 
give  the  same  results.  Locomotive  power  is  more  independent 
in  these  animals  than  in  mammals.  In  fish,  ablation  of  the  brain, 
with  preservation  of  the  parts  representing  the  pons,  allows  of 
the  subsistence  of  a  sort  of  spontaneity,  no  doubt  apparent,  and 
which  is  due  to  the  persistence  of  the  stimuli  to  which  the  animal 
left  in  its  own  medium  is  exposed.  A  frog  with  the  brain  removed 
remains  motionless  ;  placed  in  water  it  swims  (by  reflex  stimula- 
tion from  the  medium)  until  it  reaches  the  edge,  when  it  again  becomes 
motionless.  A  bird  after  ablation  of  the  brain,  if  placed  on  the  ground, 
also  remains  motionless  ;  thrown  in  the  air,  it  flies,  to  sustain  itself 
until  it  once  more  falls  to  the  ground.  In  both  cases  the  mechanism  is 
the  same. 

A  voluntary  impulse  transmitted  from  the  brain  to  the  pons  finds 
in  this  organ  a  ready  formed  nervous  mechanism  which  it  puts  into 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    361 

action,  and  by  which  comphcated  movements  are  brought  about, 
without  its  taking  part  in  their  detail.  It  acts  itself  as  a  stimulus 
conveyed  from  the  exterior  by  the  sensory  nerves. 

Pre-established  associations. — The  functional  associations  effected  in  the  pons 
for  the  performance  of  locomotion  are  the  result  of  embryological  development, 
and  are  not  acquired  by  education.  At  least  this  may  be  asserted  with  regard 
to  certain  species  both  of  mammals  and  birds.  The  young  of  the  rabbit  do  not 
walk  imtil  they  are  several  weeks  old  ;  it  is  the  same  with  dogs,  and  several 
bu'ds  (pigeon,  sparrow,  etc.).  On  the  contrary,  the  guinea-pig  can  walk  as  soon 
as  it  is  born;  and  so  can  the  chicken  and  the  duckling.  Every  one  is  acquainted 
with  the  fact  that  ducklings  hatched  by  the  hen  will  take  to  the  water  directly 
they  leave  the  egg,  and  swim  without  any  need  of  apprenticeship  or  imitative 
education.  It  may  also  be  allowed  that,  in  man  himself,  walking  and  the  upright 
position  are  facts  of  develoj^ment  rather  than  of  education. 

A.  Respiration. — Experiments  have  long  shown  that  the  survival 
of  animals  is  compatible  with  mutilations,  with  very  extensive  curtail- 
ments of  the  nervous  system,  when  these  are  effected  on  its  superior 
portion  (brain,  cerebellum,  basal  ganglion),  or  on  the  inferior  portion 
(spinal  cord  as  far  as  the  neighbourhood  of  the  middle  of  the  cervical 
region)  ;  while  very  hmited  lesions  brought  to  bear  on  the  intermediate 
region  may  bring  about  death  in  a  sudden  manner,  and  without  any 
return  of  the  functions  (Galen,  Lory).  This  is  because,  as  Legallois 
has  pointed  out,  the  mutilation  at  this  point  attacks  nervous  organs 
governing  respiration  ;  and,  although  this  function  in  itself  may  not 
be  more  important  than  others  (alimentation  for  example),  the  move- 
ments maintaining  it  can  suffer  no  delay,  because  the  reserves  of  oxygen 
are,  in  the  organism,  extremely  small  in  quantity  in  proportion  to 
those  of  other  substances.  If  pulmonary  ventilation,  oxygenation  of 
the  blood  and  of  the  tissues  is  arrested,  the  general  sequence  of  functions 
is  interrupted  ;    life  cannot  be  maintained. 

1.  Vital  knot. — Legallois  observed  that  the  lesion  may  be  limited 
to  a  small  space  near  the  origin  of  the  pneumogastric  nerves.  Flourens 
endeavoured  to  define  still  more  clearly  the  locality  of  this  area,  which 
he  calls  central  motor  of  respiration,  or  vital  knot  (nceud  vital).  After 
some  alterations  he  located  it  in  the  depth  of  the  bulb  at  the  tip  of  the 
V  of  grey  substance  enclosed  in  the  posterior  angle  of  the  fourth  ven- 
tricle, and  he  extended  it  to  right  and  left  of  the  median  hne  for  about 
two  or  three  millimetres  from  the  latter,  for  this  centre  is  double  ; 
respiration  and  life  only  cease  when  both  sides  are  destroyed.  The 
operation  was  performed  by  plunging  a  punch  of  the  dimensions 
indicated  into  the  bulbar  matter. 

Dissociation  of  the  respiratory  movements. — If  the  lesion  is  made  immediately 
behind  the  tip  of  the  V,  the  resjiiratory  movements  of  the  trunk  are  abolished, 


362  SYSTEMATIC    FUNCTIONS 

those  of  the  face,  however,  subsisting  some  time  longer  ;  if  made  immediately  in 
front  of  the  V,  the  converse  happens  ;  the  movements  of  the  trunk  persist,  while 
those  of  the  face  are  abolished. 

Situation  and  depth. — Longet,  who  has  repeated  these  exjaeriments,  maintains 
that  the  mutilation  producing  these  effects  mixst  bear  upon  the  lateral  tract  of 
the  bulb. 

In  endeavouring  to  perform  the  experiment  of  Floiu'ens,  a  considerable  number 
of  observers  have  been  induced  to  displace  or  extend  the  respiratory  centre 
whose  limits  were  fixed  by  liim.  From  the  contradictions  which  have  arisen 
between  them  on  this  subject,  Wertheimer  draws  the  conclusion  that  it  is  not 
possible  to  limit  this  centre  in  a  more  definite  manner  than  Legallois  has  done. 
It  is  a  locality  of  grey  substance  enclosed  in  the  inferior  triangle  of  the  floor  of 
the  fourth  ventricle  and  comprehending  its  deep  layers. 

According  to  an  arrangement  which  is  found  in  all  systems  of  the  same  nature, 
the  bulbar  centre  of  Legallois  is  superposed  to  the  medullary  centres  from  which 
the  motor  nerves  of  respiration  directly  emanate.  It  associates  and  co-ordinates 
them,  making  use  of  their  aptitudes.  Reduced  by  the  separation  of  the  spinal 
cord  and  of  the  medulla  oblongata  to  the  emiiloyment  of  their  own  unaided 
functions,  these  latter  can  still  for  a  time  maintain  rhythmic  movements  capable 
of  oxygenating  the  blood. 

These  movements  of  spinal  origin  are  not  observable  in  the  conditions  habitual 
to  the  destruction  of  the  bulb,  or  to  the  experiment  of  Flourens,  becavise  the 
shock  of  operation  prevents  their  production,  and  respiration,  allowing  of  no 
delay,  deatli  at  once  supervenes.  This  difficulty  is  removed  by  maintaining 
artificial  respiration  until  the  effects  of  the  shock  are  dissipated  (Wertheimer), 
or  by  re-awakening  the  medullary  excitability  by  strychnine  (Langendorff),  or 
by  rhythmically  exciting  the  sensory  nerves  of  the  thorax,  which  permits  of 
respiration  being  maintained  by  exclusively  spinal  reflexes  (Chauveau). 

Respiratory  hemiplegia. — According  to  Schiff,  hemisection  of  the  spinal  cord 
below  the  l^ulb  ])roduces  respiratory  hemiplegia,  by  rendering  a  portion  of  the 
diaphragm  and  the  corresponding  muscles  immobile.  Bvit  this  hemiplegia  is 
not  constant,  and,  when  the  stimuli  are  exaggerated,  the  paralysed  side  parti- 
cipates in  the  ventilation  of  the  lung.  If,  for  example,  the  phrenic  nerve  of  the 
side  opposite  to  the  hemisection  be  cut,  it  is  the  side  of  the  hemisection  alone 
which  contracts.  Commissures  existing  between  the  nuclei  of  the  i)hrenic  nerve 
would  ensure  this  transmission  of  impulses. 

It  is  possible  by  a  longitudinal  section  to  separate  the  two  halves  of  the  medulla 
oblongata  :  respiration  persists  and  remains  synchronous  ;  or,  on  the  other  hand, 
the  two  halves  of  the  cervical  spinal  cord  may  be  separated,  and  the  result  is 
the  same.  Connexions  exist  in  both  cases  sufficient  to  solidarize  the  two  halves 
partially  separated. 

2.  Influence  of  the  composition  of  the  blood. — Like  all  centres  of  the 
same  order,  the  respiratory  centres  operate  in  a  reflex  manner  under 
the  influence  of  the  impulses  which  they  receive  by  their  sensory  nerves  ; 
but  they  are  further  affected  by  the  quality  of  the  blood  passing  through 
them.  The  loiceriyig  of  tension  of  oxygen  in  the  blood,  the  augmentation 
of  that  of  carbonic  acid,  increases  their  excitability.  The  movements  of 
respiration  are  augmented.  The  conditions  of  vitiation  of  the  internal 
medium  are  thus  the  same  as  those  which  increase  the  removal  of  its 
gases,  and  permit  the  ventilation  to  be  regulated  according  to  the 
composition  of  the  blood. 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    363 

Defensive  reflexes. — The  regular  movement  of  respiration  is  converted,  under 
certain  influences,  into  a  defensive  movement  of  expulsion  by  exaggeration  of 
the  expiratory  current  of  air,  as  in  coughing  and  sneezing  ;  these  reflex  acts  are" 
brought  about  by  special  sensory  stimuli  limited  to  certain  regions,  acting  on 
mucous  membranes  either  in  theu*  normal  condition  or  after  having  undergone 
a  certain  amovmt  of  inflammation. 

Cough. — Cough  arises  from  stimulation  of  the  extremities  of  the  laryngeal 
nerves  (prmcipally  the  superior  laryngeal),  and  preferably  in  certain  localities. 
An  area  vei*y  efficacious  for  the  production  of  cough  (in  the  normal  condition  of 
animals)  is  the  interarytenoid  space  of  the  glottis,  towards  the  posterior  extremity 
of  the  vocal  cords  (Vulpian).  To  a  slighter  degree,  the  areas  innervated  by  the 
recuiTent  provoke  coughing,  even  after  section  of  the  superior  laryngeal  nerves 
(Longet),  and  bring  about  the  expulsive  cough  which  protects  the  respiratory 
tracts  during  swallowing.  Other  areas  of  this  description  exist  in  the  pharynx 
and  in  the  soft  palate,  in  the  nasal  fossae,  in  the  auditory  meatus,  etc. 

Direct  stimulation  of  the  floor  of  the  foui'th  ventricle  produces  cougliing. 

Sneezing. — The  starting  point  of  the  stimulus  is  not  the  organ  of  olfaction,  bat 
the  sensory  elements  of  the  olfactory  mucous  membrane  furnished  by  the  tri- 
geminal (ethmoid  filament  of  the  ophthalmic  branch).  Neither  is  it  the  stimula- 
tion of  the  retina,  when  sneezing  results  from  the  impression  produced  by  a  vivid 
light,  but  it  lies  in  the  extremities  of  the  ciliary  nerves  (Wertheimer  and  de 
Surmont). 

Vomiting. — In  the  reflex  act  of  vomiting,  contraction  of  the  diaphragm  (modi- 
fied resjiiratory  movement)  is  associated  with  movements  of  the  mouth  and 
contractions  of  the  stomach.  The  principal  association  of  the  sensori-motor 
nerves  of  these  different  organs  occurs  in  the  medulla  oblongata.  A  dog  sub- 
jected to  the  influence  of  tartar  emetic,  after  sub-bulbar  section  of  the  spinal 
cord,  merely  performs  movements  of  the  mouth  and  neck  without  any  rejection 
of  food  (Gianuzzi).  Nevertheless,  the  possibility  of  acting  in  a  reflex  manner  on 
the  diaplu'agm,  after  section  of  the  spinal  cord,  is  demonstrated  by  stimulation 
of  the  central  end  of  the  splanchnic  nerve  (Luchsinger). 

B.  Circulation. — Like  those  of  respiration,  the  stimulating  and 
regulating  systems  of  the  movements  of  circulation  are  numerous,  and 
formed  of  layers,  to  which  localities  of  the  grey  matter,  having  for 
function  the  realizing  of  associations  of  their  constituent  parts,  corre- 
spond. Here  again  we  find  inferior  centres  and  a  superior  centre  govern- 
ing the  latter.  The  inferior  centres  are,  above  all,  the  ganglia  of  the 
great  sympathetic,  whence  directly  proceed  the  vaso-motor  and  cardio- 
motor  nerves,  which  form,  between  these  gangha  and  the  cardiac  and 
vascular  muscles,  fibres  of  projection  of  the  first  order.  These  ganglia 
are  united  to  the  spinal  cord  by  communicating  white  branches,  these, 
therefore,  being  fibres  of  projection  of  the  second  order.  The  points 
of  penetration,  or  rather  of  exit,  of  these  fibres  of  the  second  order 
(consequently  intercentral)  along  the  course  of  the  spinal  cord  is  very 
precisely  known.  We  are  much  less  well  informed  with  regard  to  the 
relations  entered  into  by  them  with  the  grey  medullary  matter.  After 
leaving  the  apparent  origins  which  we  recognize  as  being  theirs,  do 
they  ascend  directly  as  far  as  the  grey  medullary  matter,  or  are  they 


364  SYSTEMATIC    FUNCTIONS 

reinforced  in  the  grey  medullary  nuclei  which  correspond  to  them  ? 
Or,  once  again,  do  they  present  a  mixture  of  these  two  arrangements  ? 
These  different  opinions  have  all  had  partisans. 

1.  General  bulbar  vaso-motor  centre. — It  is  especially  to  physiology 
that  we  look  for  a  solution  of  this  problem.  The  centres  thus  sought 
for  are  indicated  functionally  by  the  tonic  action  which  they  exert  on 
the  vascular  pressure.  By  making  progressive  sections,  or  by  destroy- 
ing given  areas  along  the  grey  axis,  and  noticing  each  time  the  state 
of  the  pressure,  we  shall  see,  by  its  changes  or  its  persistence,  if  these 
centres  exist  or  are  wanting,  and  in  what  their  function  consists. 

Spinal  and  ganglionic  centres. — Sub-bulbar  section  of  the  spinal  cord 
at  first  produces  a  considerable  fall  of  pressure.  This  very  evident 
fact  has  been  brought  forward  as  proof  of  the  existence  of  a  general 
and  single  centre,  situated  in  the  medulla  oblongata,  in  the  neighbour- 
hood of  the  calamus  (Schiff).  But  if,  by  artificial  respiration,  the  life 
of  the  animal  be  prolonged,  it  will  be  seen  after  a  certain  time  that  the 
vascular  tonicity  is  re-established  and  the  pressure  raised.  It  may  be 
increased  by  asphyxial  stimulation,  or  by  the  action  of  strychnine  ; 
the  remaining  tonic  power  is  then  shared  by  the  spinal  cord  and  the 
ganglia  of  the  great  sympathetic.  B}^  an  experiment  of  the  same 
nature  consisting  in  removal  of  the  largest  part  of  the  spinal  cord,  Goltz 
and  Ewald  have  also  shown  that,  after  a  fresh  fall,  the  vascular  tonus 
may  be  re-established  by  the  only  subsisting  action,  that  of  the  great 
sympathetic.  It  is  better  then  to  refrain  from  judging  directly  from 
the  immediate  effect,  which  is  not  definitive,  but  to  realize  that,  after 
a  period  of  shock,  the  system,  in  spite  of  its  equilibrium  being  thus 
destroyed,  retains  in  itself  the  means  of  re-establishing  to  a  certain 
degree  the  disturbed  function,  and  employs  for  this  purpose  the  resources 
of  its  associations  still  left  intact.  From  what  has  just  been  said,  it  is 
proved  that  these  associations  exist  in  the  ganglia,  in  the  spinal  cord, 
and  in  the  medulla  oblongata,  these  latter  possessing  the  very  highest 
importance  for  the  regulation  of  the  vaso-motor  function. 

2.  Vaso-motor  reflexes. — Another  property  of  the  centres  is  that  of 
reflecting  impulses  conveyed  to  them  by  the  path  of  the  sensory  nerves. 
Stimulation  of  an  important  sensory  nerve,  such  as  the  trunk  of  the 
sciatic,  produces,  by  reflex  action,  a  marked  elevation  of  pressure.  If 
by  successive  operations  different  portions  of  the  brain  and  the  ence- 
phalon  are  removed,  these  reflex  actions  still  remain  possible  as  long 
as  the  medulla  oblongata  is  intact  (Dittmar).  They  cease  directly  the 
bulb  is  separated  from  the  spinal  cord  (Owsjanikow).  These  experi- 
ments seem  in  a  very  distinct  manner  to  define  at  the  same  time  both 
the  situation  and  the  limits  (in  height)  of  the  vaso-motor  centre.     They 


CONSCIOUS  AND  UNCONSCIOUS  :    THEIR  SEPARATION    365 

also  indicate  the  bulb  as  containing  this  centre,  which  is  at  the  same 
time  single  and  independent.  They  certainly  give  it  a  preponderating 
importance,  but  they  ought  to  be  verified  by  other  and  decisive  proofs. 

Here  again  it  is  necessary  to  distinguish  between  immediate  and 
consecutive  results.  Once  the  shock  of  the  operation  over,  it  may  be 
possible  that  the  sensory  stimulus  (even  in  the  case  of  sub-bulbar  sec- 
tion) may  exert  its  reflex  effect  of  elevation  of  pressure.  It  must  be 
then  that  the  stimulated  sensory  nerves  reach  in  the  spinal  cord  itself 
centres  of  reflexion  resembling  the  bulbar  centre,  which  are  less  power- 
ful, that  is  to  say,  less  qualified,  for  generalizing  the  stimulus  to  the 
whole  vaso-motor  system,  but  able  to  perform  this  function  to  a  certain 
degree.  The  bulbar  centre  may,  for  its  part,  under  certain  conditions, 
obey  the  impulses  descending  from  the  cerebral  cortex. 

Cardio-inhibitory  centres. — Thus  there  is  in  the  medulla  oblongata 
a  centre  for  the  association  of  impulses  which  harmonizes  other  centres 
of  association  placed  in  dependence  on  it.  These  are  gradated  in  the 
grey  bulbo-medullary  axis  in  such  a  manner  that  those  placed  highest 
are  situated  almost  in  the  immediate  neighbourhood  of  the  vaso-motor 
centre.  Amongst  these  are  the  nuclei  of  origin  of  the  cardio-moderator 
nerves  contained,  according  to  certain  authors,  in  those  of  the  pneumo- 
gastric  ;  others,  it  is  true,  locate  them  a  little  lower,  in  those  of  the  spinal 
accessory  (Waller)  ;  of  this  number  also  are  the  nuclei  of  origin  of  other 
vaso-motor  nerves  (principally  dilators),  going  to  the  tongue,  to  the 
sub-maxillary  gland,  etc.  T'he  medulla  oblongata,  the  thoracic  and 
the  sacral  spinal  cord,  are,  as  has  already  been  said,  the  three  principal 
localities  (at  least  apparently  so)  for  the  origin  of  nerves  which  either 
by  the  sympathetic  chain  (thoracic  region),  or  outside  it  (bulbar  and 
sacral  region),  proceed  to  the  heart  and  the  vessels.  A  characteristic 
feature  of  the  medulla  oblongata  is  that  of  being  at  the  same  time  a 
continuation  of  the  spinal  cord  by  the  nuclei  of  origin  prolonging  the 
gr.ey  axis,  and  also  a  superadded  formation,  by  the  supplementary  grey 
masses  which  have  no  longer  any  connexion  with  the  periphery  except 
by  the  preceding  nuclei,  to  which  they  are  united  by  hnks,  contributing 
to  form  the  white  tracts  of  the  spinal  cord  and  of  the  bulb. 

C.  Movements  of  the  pupil. — The  movements  of  the  pupil,  which 
are  very  easy  to  observe,  have  also  served  for  determining  the  con- 
nexions of  the  great  sympathetic  with  the  spinal  cord  and  the 
medulla  oblongata. 

1.  Dilator  reflex  of  the  iris. — The  apparent  origin  of  the  dilator 
nerves  of  the  pupil  is  in  the  cervico-thoracic  region  of  the  spinal  cord. 
Budge  localizes  a  cilio-spinal  centre  in  this  region.  Chauveau  has 
observed  that,  if  the  spinal  cord  be  cut  in  the  cervical  region  (between 


366  SYSTEMATIC    FUNCTIONS 

this  centre  and  the  bulb),  stimulation  of  a  jJosterior  thoracic  root  will 
still  cause  the  pupil  to  dilate  by  reflex  action  on  the  spinal  cord.  The 
bulbar  centre  is  not  indispensable  for  this  reflexion.  Some  authors 
have  noticed  the  possibility  of  this  effect  being  induced  after  the  separ- 
ation of  the  bulb  (Salkowsky).  It  must  be  remembered  that  the 
medullary  power  of  reflexion  is  impaired  by  the  shock  succeeding  the 
section,  and  reappears  only  after  a  certain  period  of  repose.  And  it 
must  also  be  noticed  that  the  dilators  of  the  iris  arise  not  only  from 
the  thoracic  spinal  cord  by  the  cervical  great  sympathetic,  but  also 
from  the  special  origins  of  the  trigeminal  itself,  by  fibres  representing 
the  cranial  or  bulbar  portion  of  the  origins  of  the  great  sympathetic, 
and  that  after  the  separation  of  the  spinal  cord  and  the  bulb,  these 
latter  being  put  out  of  court,  the  dilatory  action  of  the  stimulation  is 
by  just  so  much  diminished.  The  irido-dilator  reflex  in  these  experi- 
ments has  a  sensory  stimulus  for  starting  point  (posterior  root  or  some 
kind  of  sensory  cutaneous  nerve). 

2.  Irido-constrictor  or  photo-regulative  reflex. — Another  reflex  exists 
which  is  antagonistic  to  the  preceding  one,  and  has  for  its  starting 
point  a  sensorial  stimulation  of  the  optic  nerve,  revealing  itself  by  the 
contraction  of  the  pupil  at  the  approach  of  a  strong  light.  This  reflex, 
pointed  out  for  the  flrst  time  by  Herbert  Mayo,  has  the  retina  and  the 
optic  nerves  for  its  centripetal  paths,  the  anterior  corpora  quadrigemina 
for  locality  of  reflexion,  and  for  paths  of  return  to  the  constrictor 
muscles  of  the  iris,  fibres  which,  arising  in  one  of  the  partial  nuclei  of 
the  oculo-motor  nerve,  follow  this  nerve,  pass  through  the  ophthalmic 
ganglion,  to  terminate  by  ciliary  nerves  in  the  ciliary  plexus  and  by 
it  in  the  iris.  This  reflex  system,  instead  of  having  its  paths  divided 
between  the  spinal  cord  and  the  medulla  oblongata,  has  them,  on  the 
contrary,  concentrated  in  this  latter  organ  and  in  the  nerves  which 
either  start  from  it  or  terminate  in  it.  In  any  case,  if  there  are  medul- 
lary paths,  there  are  no  means  of  demonstrating  their  existence. 

Whether  one  or  the  other  of  these  two  reflexes  is  in  question,  there  are 
certainly,  in  addition  to  local  centres  of  emergence  of  the  motor  nerves  and  of 
termination  of  the  sensory  nerves,  one  or  more  centres  of  association.  For  the 
photo-regulatory  reflex  these  centres  are  near  each  other  (corpora  quadrigemina, 
nuclei  of  the  oculo-motor  nerve,  longitudinal  bundle) ;  for  the  irido-dilator  reflex 
they  are  separated  by  a  great  distance  (medulla  oblongata,  thoracic  spinal  cord, 
ground  bundle)  ;  thus  their  experimental  dissociation  becomes  easy,  and  when 
effected  by  section  of  the  cervical  spinal  cord,  it  shows  that  the  reflex  associations 
persist  in  the  inferior  centre  between  sensoi'y  and  motor  nerves  brought  into 
relation  by  its  grey  matter. 

D.  Secretions. — The  preceding  scheme  is  applicable  to  the  vaso- 
motor system,  and  also  to  that  of  the  secretory  nerves.     Whether  the 


CONSCIOUS  AND  UNCONSCIOUS  :  THEIR  SEPARATION      367 

cutaneous  covering  or  the  intestine  with  its  large  appendant  glands  be 
in  question,  it  is  almost  superposable  to  it.  The  same  distribution  of 
nerves  to  the  periphery  ;  the  same  origins  in  the  chain  and  in  the  spinal 
cord  and  the  medulla  oblongata  ;  the  same  subordination  of  inferior 
systems  to  a  bulbar  centre  of  association,  and  the  same  conditions 
bringing  into  relief  the  predominating  part  played  by  this  centre  and 
the  existence  of  the  inferior  systems. 

In  the  restricted  space  allotted  to  the  respiratory  centre,  and  to  the 
general  vaso-motor  centre,  experiment  demonstrates  the  existence  of 
other  localities  of  association,  which  act  in  an  analogous  manner  on  the 
phenomena  of  glandular  activity.  The  influence  of  the  medulla  ob- 
longata extends  to  the  renal  secretion,  the  secretions  of  the  digestive 
tract,  and  the  cutaneous  secretion  ;  it  also  governs  what  are  called 
internal  secretions,  of  the  same  nature  as  that  of  the  formation  of  glucose 
at  the  expense  of  glycogen  of  the  liver.  This  is  proved  by  the  following 
facts. 

Diabetic  puncture. — Glycosuria. — C'l.  Bernard  Jias  shown  that  by  puncturing 
the  floor  of  tlie  foiu'tli  Aentricle  at  a  given  point,  situated  on  the  median  line  and 
in  the  space  whicli  separates  the  origin  of  the  two  pneuniogastrics,  the  appearance 
of  sugar  in  the  urine  is  provoked  ;  the  glycosuria  commences  from  the  first  hoiu- 
following  the  operation  and  disappears  after  foiu'  or  five  hours  :  from  this  we 
may  conclude  that  the  puncture  acts  as  a  stimulus. 

Polyuria. — If  the  piuicture  is  effected  a  little  higher,  in  the  space  comprised 
between  the  origins  of  the  acoustic  and  pneumogastric  nerves,  polyuria  and 
glycosvu"ia  will  appear  simultaneously.  These  two  phenomena  are  further  most 
frequently  associated. 

Albuminuria. — If  the  punctm'e  be  carried  out  still  higher  up,  between  or  above 
the  origin  of  the  acoustic  ner^'es,  polyiu'ia  alone  may  ap2;)ear,  with  or  ■wathont 
albuminuria. 

Salivation. — CI.  Bernard  has  also  noticed  that  salivation  may  be  provoked  by 
puncturing  the  fourth  ventricle.  The  occurrence  of  glycosuria  suggests  the 
existence  of  a  connexion  between  the  bulb  and  the  liver,  this  latter  being  the 
glyco-secretory  organ,  and  the  more  so  because,  after  the  jiuncture,  an  elevation 
of  the  proportion  of  glucose  in  the  arterial  blood  is  observed,  and  this  effect  (hyper- 
glycsemia  and  glycosuria)  no  longer  results  when  the  branches  of  the  great 
sympathetic  rtmning  to  the  liver  have  been  previovisly  cut. 

Poljairia  p«ints  to  a  connexion  with  the  kidney,  and  hy2)ersa]ivation  to  one 
witli  tlie  salivary  glands. 

Reflex  secretions. — These  different  glandular  activities  may  be  pro- 
voked in  a  reflex  manner  by  stimulation  of  certain  sensory  nerves. 
Hyperglycsemia  has  been  observed  after  stimulation  of  the  central  end 
of  the  vagus  (CI.  Bernard),  glycosuria  and  hyperglycfemia  after  that 
of  the  depressor  nerve  (Filehene,  Laffont).  These  reflex  effects  are  no 
longer  produced  when  the  region  in  the  bulb  corresponding  to  the  point 
Avhere  the  puncture  is  made  has  been  destroyed. 

Sudation.— Stimulation  of  the  sensory  nerves  usually  produces  a 


368  SYSTEMATIC    FUNCTIONS 

reflex  action  of  the  sweat  glands.  Without  seeking  to  define  narrowly 
the  region  where  this  reflexion  occurs,  the  question  has  been  raised 
(just  as  it  has  been  for  the  vaso-motor  nerves)  as  to  whether  the  spinal 
cord  or  the  medulla  oblongata,  or  both  together,  are  concerned  in  it, 
and  if  so,  in  what  measure.  While  the  medulla  oblongata  retains  its 
connexions  with  the  spinal  cord,  reflex  sudation  is  easily  effected. 
After  sub-bulbar  section,  according  to  some  authors,  this  reflexion 
ceases  (Nawrocki)  ;  .  according  to  others,  it  persists  in  a  restricted 
manner  (Luchsinger,  Robillard).  This  latter  opinion  is  the  true  one  ; 
only  it  is  necessary  that  stimulation  should  not  be  applied  for  a  certain 
time  (perhaps  twenty  minutes,  or  half  an  hour)  after  section  of  the 
spinal  cord,  to  allow  time  for  the  shock  of  the  operation  to  pass  off  : 
life  is  maintained  by  pulmonary  insufflation. 

Connexions  between  parallel  systems. — As  a  whole,  the  systems  governing 
the  circulatory  and  secretory  functions  closely  resemble  each  other.  Their 
nerves  pass  into  the  chain  and  the  ganglia  of  the  great  sympathetic  ;  for  the 
same  organs  they  are  contained  in  the  same  trunks  and  leave  the  spinal  cord 
by  the  same  roots.  We  have  just  seen  that  these  systems  possess  a  common 
locality  of  systematization  in  the  grey  substance  of  the  medulla  oblongata,  with- 
out prejudice  to  those  which  they  present  in  the  sympathetic  ganglia  and  in 
the  sjjinal  cord.  This  vicinity  of  their  elements  and  this  penetration  of  their 
centres  indicate  functions  which  are  not  only  parallel,  bvit  in  a  certain  degree 
dependent  the  one  on  the  other,  or  which  are  at  any  rate  regulated  the  one  by 
the  other.  These  functional  associations  imply  connexions,  in  the  different 
localities  of  the  grey  matter,  between  the  two  systems.  The  grey  masses 
which  we  call  vaso-motor,  secretory,  or  other  centres,  should  therefore  be  con- 
sidered not  as  organs  Avith  definite  boundaries,  but,  once  again,  as  a  complex 
assemblage  of  connexions  which  can  be  made  or  severed  according  to  the  require- 
ments of  the  function. 

BIBLIOGRAPHY. 

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Regas-Nicolaides,  Trajet  des  vaso-moteurs.  Arch.  f.  Anat.  und  Phys.,  1882. — Ollivier, 
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CONSCIOUS  AND  UNCONSCIOUS  :  THEIR  SEPARATION     369 

de  la  phys.,  18o9. — Vax  Deen,  Traites  et  decoiivertes  sur  la  physiol.  de  la  moelle  epin., 
Leyde,  1841  ;  Froriep's  Neue  Notizen,  1843. — Vulpian,  Art.  "  Moelle,"  Diet,  de  Dechamhre 
(bibliographie). — Waller,  Biol.,  1855. — Wertheimer,  C.  R.  Acad,  sc,  1886,  t.  CII, 
p.  520. 

Posterior  columns. — Bechterew,  Arch.  f.  Anat.  und  Phys.,  1890,  p.  489. — Brown- 
Skquard,  Journ.  de  la  physiol.  de  Vhomme  et  des  animauz,  1863.— Engelken,  Arch,  de 
Du  Bois-Reymond,  1867,  p.  198. — Fodera,  Journ.  de  phys.  exper.,  1823,  t.  Ill,  p.  191. — 
G1.A.NNUZZI,  Centralbl.,  1873,  p.  824. — Jacob  et  Bickel,  Arch.  f.  Anat.  und  Phys.,  1900. 
— Pfllger,  Die  sensoriscli.  Fonct.  d.  Riickenmarks. — Pierret,  Arch,  de  phys.,  1872, 
p.  364. — Rolando,  Journ.  comjilem.  du  Diet,  des  sc.  med.,  1828,  t.  XXX,  pp.  159  et  204. — 
ScHiFF,  C.  R.  Acad,  sc.,  1854  et  1862;  Lehrb.  d.  Phys.  ;  Gaz.  hebd.,  1859  et  1872.— 
ScHOPS,  Arch,  de  Meckel,  1827  :  Journ.  complem.  du  Diet,  des  sc.  med.,  1828,  t.  XXX, 
p.   114.— Troisier.  Arch,  de  phys.,   1873,  t.  V,  p.  709. 

Anterior  and  lateral  columns. — Ditt.al\r,  Sachs.  Ges.  d.  Wiss.,  1870. — Hxjizikga, 
Pfliiger's  Arch.,  1870,  t.  Ill,  p.  81. — Mendelssohn,  Arch.  /.  Anat.  und  Phys.,  1883, 
p.  281. — MiscHER,  Arbeit,  phys.  Anstalt.  zu  Leipzig,  1870. — Nawrocki,  Arbeit,  phys. 
Anstalt.  zu  Leipzig.  1870. 

Hemisection  of  the  spinal  cord. — Bottazzi,  Arch.  ital.  de  biol.,  1895,  t.  XXR^  p.  466. 
— HoMEN,  Lesions  par  hemisect.,  C.  R.  Acad,  sc,  1883,  t.  XCVI,  p.  1681. — Oppenheim, 
Zur  Br.  Seq.  Lahmung,  Arch.  f.  Anat.  und  Phys.,  1899,  Suppl.  p.  1. 

Trophic  disturbances. — Angelucci,  (Eil,  Arch,  ital.]  de  biol.,  1894,  t.  XX,  p.  67. 
Bentivegna,  Vague  et  symp.  pneuni.  exper..  Arch.  ital.  de  biol.,  1895,  t.  XXIV,  p.  243. 
— Brown-Sequard,  Biol.,  1850,  et  Journ.  de  la  phys.,  1863. — G.  Fantino,  Myoearde, 
Arch.  ital.  de  biol.,  1888,  t.  X,  p.  237. — Floresco,  Arch,  des  sc.  medicales,  1899  et  1900. — 
MoRAT  et  DoYON,  C.  R.  Acad,  sc,  1897,  t.  CXXV,  p.  124. — Morpuroo,  Regen.  cell, 
paralys.  vaso-mot..  Arch.  ital.  de  biol.,  1890,  t.  XIII,  p.  342. — S.^lvioli,  Arch.  ital.  de 
biol.,  1895,  t.  XXII,  p.  259. 

Different  degenerations  and  alterations. — ^Dejerine,  Alter,  des  nerfs  cutanea  de 
escarres,  affect.  medulL,  Arch,  de  phys.,  1882,  t.  IX,  p.  499. — Grunbau.m,  Journ.  of 
Phys.,  1894,  \o\.  XVI,  p.  368. — Gurrieri,  Empoisonnem.  phosphore.  Arch.  ital.  de 
biol.,  1896,  t.  XXVI,  p.  370. — Lamy,  Embolies  experim..  Arch,  de  phys.,  1895,  p.  77. — 
Sherrington,  Second  and  tertiar  degen.,  Journ.  of  Phys.,  1885,  p.  177. — Spronck, 
Anemie  passagere,  Arch,  de  phys.,  1888.— Tschiriew,  Lepre,  Arch,  de  phys.,  1879,  p.  614. 
— Vassale  et  DoNACiGio,  Alter,  apres  extirp.  glandes  para-thyroid..  Arch.  ital.  de  biol., 
1897,  t.  XXVII,  p.  124. 

Spinal  cord  in  those  who  have  undergone  amputation. — Hayem  et  Gilbert,  Arch, 
de  phys.,  1884.— Pellizi,  Arch.  ital.  de  biol.,  1893,  t.  XVIII,  p.  26.— Vulpian,  C.  R. 
Acad,  sc,  1872,  t.  LXXIV,  p.  462. 

Great  Sympathetic. 

Constitution  and  relations. — Birge,  Xombre  des  fibres  et  des  cellules.  Arch.  f.  Anat. 
und  Phys.,  1882. — W.-H.  Gaskell,  Journ.  of  Phys.,  1886,  p.  1. — Langley,  Journ.  of 
Phys.,  1891,  p.  375  :  Larger  medull.  fibres.  Ibid.,  1892,  p.  786. — Macinien,  Rapp.  avec 
les.  n.  craniens,  C.  R.  Acad,  sc,  1887,  t.  CIV.  p.  77. — Rochas,  Gangl.  cerv.  sup.,  C.  R. 
Acad,  sc,  1887,  t.  CIV,  p.  865. 

Degeneration  ;  regeneration  ;  chromatolysis. — Eve,  Activite  et  repos,  Journ.  of 
Phys.,  1896,  p.  334  :  Action  de  la  temper.,  Ibid.,  1900,  1,  p.  119. — Langley,  Regener., 
Journ.  of  Phys.,  1895,  t.  XVIII,  p.  280  :  Degener.,  Ibid.,  1900,  p.  468. — Lubimoff, 
Atroph.  muscul.  progress,  spinale.  Arch,  de  phys.,  1874,  p.  889. 

Ganglia  ;  reflex  and  inhibitory  action.— Dastre  et  Morat,  Pouvoir  tonique  et  inhib., 
C.  R.  Acad,  sc,  1883,  t.  XCVI,  p.  446.— Fr.-Franck,  Arch,  de  phys.,  1894,  p.  717.— 
Langley,  Axon-refiex,  Journ.  of  Phys.,  1900. — Phisalix,  Mouvements  des  chromato- 
phores  des  cgphalopodes,  Arch,  de  phys.,  1892  et  1894. — P.  Schultz,  Arch.  f.  Anat. 
und  Phys.,  1898,  p.  124. — Wertheimer,  Arch,  de  phys.,  1890,  p.  519. — Wertheimer 
et  Lepage,  C.  R.  Acad,  sc,  1899,  t.  CXXIX,  p.  737.— White,  Journ.  of  Phys.,  1887, 
p.  66,  et  1889,  p.  341. 

Innervation  of  the  heart. — Engeljl\nn,  Methods  d'observ.  Arch.  f.  Anat.  und  Phys., 
1900,  p.  178  et  p.  315. — Heymans,  Arch.  f.  Anat.  und  Phys.,  1893. — Lahotjsse,  Arch, 
f.  Anat.  und  Phys.,  1886. — Xicola.jeff.  A)ch.  f.  Anat.  ^ind  Phys.,  1893. 

Periodic  inexcitability  :  refractory  phase  :  extra-systole  ;  post-compensatory 
systole  ;  conservation  of  the  work  of  the  heart,  etc. — Voy.  Circulation  (bibliographie 
du  Cceur). — Myogenic  and  nevro-genic  theories,  Voy.  Dictionnaire  de  physiologic  de 
Richet,  article  "Cceur."' 

Accelerating  innervation. — Albertoni  et  Bufalini,  Ric  Gab.  d.  Fisiol.  universita 
di  Siena,  Milan,  1876. — Baxt,  Sachs.  Ges.  d.  Wiss.,  1875  ;  Arch.  f.  Anat.  und  Phys., 
1878.— Cl.  Bernard,  Lemons  sj^st.  nerv.,  t.  I,  pp.  206  et  382,  t.  II,  p.  449.— V.  Bezold, 
Acad,  de  Berlin,  1862  ;  Journ.  Br. -Seq.,  1862  :  Siu-  I'innervation  du  ccem-,  Leipzig,  1863. 
— Budge,  C.  R.  Acad,  sc,  1852.— E.  et  M.  Cyon,  Arch.  f.    Anat.    und  Phys.,    1867  ; 

P.  B  B 


370  SYSTEMATIC    FUNCTIONS 

C.  R.  Acad,  sc,  1867  ;  Journal  de  Vanatomie  de  Robin,  1808. — Franvois-Fbanck,  Biol., 
1879;  C.  R.  Acad,  sc,  1879;  Lab.  Marej-,  1878-79;  Biol.,  1884. — Legallois,  Sur  le 
principe  de  la  vie,  Paris,  1812:  OEuvres,  1811. — Ludwig  et  Cyon,  Centralhl.  f.  med. 
Wi^sensch.,  1866  ;  Arch,  de  Du  Bois-Reymond,  1867. — Ludwig  et  Thiry,  Wien  Sitzung- 
her.    1864. — Moleschott,  Revue  hebd.  de  med.  de  Vienne,  1861,  1862,  et  Molesch.  unters., 

jg(i2. Moleschott   et   Xauwerck,   Molesch.   unters.,    1861. — Moleschott  et   Huf- 

SCHMIDT,  i6i(i.,  1862. — Re ynier.  These  agr.,  Paris,H860. — Schiff,  .4/-c7i.  /.  phys.  Heilk., 
1849  ;  Lehrb.  d.  Phys.,  1858  ;  Med.  Centralbl,  1873. — Schmiedeberg,  Arbeit,  a.  d.  phya^ 
Lab.,  Leipzig,  1871. — Traube,  Berl.  klin.  Wochensch.,  1866. — Volkmann,  Mailer's 
Arch.,  1845.^Werthei:\ier,  Echo  medic,  du  Nord,  1898. — Wilson  Philifp,  Bibl.  univ. 
de  Geneve,  t.  I. 

Moderating  innervation. — Voy.  Circulation  et  Nerfs  craniens,  Pneiimogastrique. 

Vaso-motor  and  secretory  innervations. — Voy.  Circulation  et  Secretion. 

Heart  ooisons. — Cyon,  Revue  generale  des  sciences  pures  et  appliquees,  1901. — Filehne, 
Nitrite  d'amyle.  Arch,  de  Pflilger,  1874,  t.  IX. — Klug,  Arch.  f.  Anat.  und  Phys.,  1879, 
1880  (Dic^itaie). — Ivroneckeb,  Ether,  Arch.  f.  Anat.  und  Phys.,  1881. — Langendorff, 
Atropine,  Arch.  f.  Anat.  und  Phys.,  1886. — Schiff,  Arch,  de  Pfliiger,  1871. — S.  Schmidt, 
Chloroforme,  Arch.  f.  Anat.  und  Phys.,  1897. — Weinzweig,  Muscarine,  Arch.  f.  Anat. 
und  Phys.,   18S2. 

Cutaneous  secretions. — Arloing,  C.  P.  Acad.  sc.  1889,  t.  CIX,  p.  785  :  Arch,  de  phys., 
1890  et  1891. — J.-X.  Langley,  Journ.  of  Phys.,  1895,  p.  296. — Luchsinger,  Arch,  de 
Pflilger,  Serie  de  memoires,  1880  et  suiv. — Xawrocki. — Vulpian,  C.  R.  Acad,  sc,  1878. 

Other  cutaneous  functions. — P.  Bert,  Xerfs  colorateurs. — Langley  et  Sherrington. 
Pilo-moteurs,  Journ.  of  Phys.,  1891,  p.  278. — Pouchet,  Color,  chez  les  poissons,  C.  R. 
Acad,  sc,  1871,  t.  LXXIII,  p.  94.3. 

Uterus. — E.  Cy'ON,  Pfliiger's  A>-ch.,  1873,  t.  VIII,  p.  349. — Frankenhauser,  Jena 
Zeitsch.,  1865. — Goltz  et  Frensberg,  Pfliiger's  Arch.,  t.  IX.  p.  552. — Hofmann  et 
V.  Basch,  Mouv.  du  col,  Wien.  med.  Jahrb.,  1876  et  1877. — Korner,  Phys.  Inst.  Breslau, 
3    cahier,   1863  ;    Centralbl.  f.  Med.,   1864. — Oser  et  Schlesinger,  Centralbl.  f.  Med., 

1379. Schlesinger,  Wien.  med.  Jahrb.,  1873,  et  1874. — Spiegelberg,  Zeitsch.  f.  rat. 

Med.,  3e  serie,  t.  II,  1857. — Vulpian,  Vaso-moteurs. 

Vesiculae  seminales. — Loeb,  Dissert.  Giessener  Henle  und  Meissner  Bericht.  Phys., 
18(^5. — Rkmy,  Biol.,  1884. 

Spleen. — Cl.  Bernard,  Lig.  de  rorganisme. — Bochefont.atne,  Th.  doct.,  Paris,  1873  ; 
Arch,  de  phys.,  1874  ;  Gaz.  mid.,  1873. — Malassez  et  Picard,  Biol.,  1878. — Oehl,  Gaz. 
med.  lomb.,  1868. — Picard,  C.  R.  Acad,  sc,  1879. — Roy%  Journ.  of  Phys.,  1882. — Schiff, 
Legons  sur  la  digestion. — Tarchanoff,  Pfliiger's  Arch.,  1873. — Vulpian,  Biol.,  1848  ; 
Cours  de  path.  exp.  et  comparee,  1873. 

Medulla  Oblongata. 

Paths  of  motor  transmission  ;  anterior  pyramids  ;  decussation. — Berger,  Neurol. 
Centralbl.,  1895. — Brown-Sequard,  Arch,  de  phys.,  1889. — Dejerine  et  Thomas, 
Biol.,  1896. — Hallopeau,  Des  paralysies  bulbaires.  These  d'agregation  de  Paris,  1875. 

Jacobsohn,  Neurol.  Centralbl.,  1895. — Magendie,  Legons  siu-  les  maladies  du  syst. 

nerv. — Pierre  Marie,  Legons  sur  les  maladies  de  la  moelle. — Muratoff,  Arch.  f.  Anat.. 
1893. — XoTHNAGEL,  Traite  cliniqvie  du  diagnost.  des  mal.  cerebr.,  1885. — Pitres,  Arch, 
de  phys.,  1884. — Sherrington,  Journ.  of  Phys.,  1885  et  1889  ;  British  med.  Journ.,  1890. 

Unvebricht,  Neurol.   Centralbl.,   1890. — Wertheimer  et  Lepage,  Arch,  de  phys., 

1896. 

Paths  of  sensory  transmission. — Auerbach,  Anat.  Anzeiger,  1889,  et  Arch.  f.  Anat. 
und  Phys..  CXXI. — Berdez,  Revue  med.  de  la  Suisse  romande,  1892. — Browtst-Sequard, 
Arch,  de  phys.,  1889. — Conty',  Gaz.  hebdom.,  1877  et  1878.— Dejerine  et  Sottas,  Biol., 
1895. — Edinger,  Deutsch.  med.  Wochenschr.,  1890. — Ferbieb  et  Turner,  Proc  of  th. 
Societ.,  1894. — Flechsxg  et  Hcesel,  Neurol.  Centralbl.,  1890. — Lcewenthal,  Revue  m.ed. 
de  la  Suisse  romande,  1885. — P.  Meyer,  .4rc/i.  /.  Psych.,  t.  XIII,  1882. — Moeli  et  Mari- 
nesco.  Arch.  f.  Psych.,  1892. — Monakow,  Neurol.  Centralbl.,  1884. — Oddi  et  Rossi, 
Arch.  ital.  de  biol.,  1891. — Singer,  Sitzungsber.  d.  K.  Acad.  Wien,  1881. — Singer  et 
Munzer,  Denkschr.  d.  K.  Acad.  Wien,  1890. 

Alternate  hemiplegia. — Laborde,  Biol.,  1877. — Senator,  Arch.  f.  Psych.,  1881. — 
Vulpian,  These  de  Paris,  1853,  et  C.  R.  Acad,  sc,  1885. 

Vital  knot. — Brown-Sequard,  Journ.  de  la  phys.,  1858. — Flourens,  C.R.  Acad, 
sc,  1851  et  1858  ;  C.  R.  Acad,  sc,  1847  ;  Soc  philom.,  1849. — Galien,  De  anat.  admi- 
nistr.,  Leipzig,  1821,  lib.  VIII,  cap.  ix,  pp.  698  et  697,  edit,  de  Kiihn. — Longet,  Arch. 
gen.  de  mid.  1847. 

Respiratory  centre.— Aducco,  Arch.  ital.  de  biol,  1899,  t.  XII,  p.  99,  et  1890,  t.  XIII, 
p.  89. — Rich.  Arnheiji,  Arch.  f.  Anat.  und  Phys.,  1894,  p.  1. — Browtst-Sequard,  Arch, 
de  phys.,  1893,  p.  131  ;  Biol.,  1887.— Christiani,  Arch.  /.  Anat.  und  Phys.,  1880,  pp.  280 
et  295,  et  1886,  p.  180. — Fredericq,  Innerv.  resp.  chez  le  Poulpe,  C.  R.  Acad,  sc,  1879, 
t.  LXXXVIII,  p.  346.— Gad,  Arch.  f.  Anat.  und  Phys.,  1893,  p.  175.— Gad  et  Mari- 


CONSCIOUS  AND  UNCONSCIOUS  :  THEIR  SEPARATION     371 

NESCO,  Arch,  da  phys.,  1893. — Gierke,  Arch.  v.  Pflilger,  1872,  t.  VII,  p.  583. — Girard, 
Rech.  sur  I'app.  resp.,  Geneve  et  Bale,  1891. — Laborde,  Traitt  de  phys. — L.\ngendorff, 
Excitation  .  .  .,  Arch.  f.  Anat.  und  Phys.,  1881,  p.  519  ;  Ibid.,  Insectes  .  .  .,  1883, 
p.  80  ;  Ibid.,  1887,  p.  237;  Ibid.,  1888,  p.  2S3  :  Ibid.,  1893,  p.  397.— Lewandowsky,  Arch, 
f.  Anat.  und  Phys.,  1896,  pp.195  et  483. — Lcewy,  Arch.  f.  Anat.  und  Phys.,  1887,  p.  472. — 
Newell  Martin  et  Booker,  Journ.  of  Phys.,  1878-79,  vol.  I,  p.  370. — 3Ieyer,  Innerv. 
resp.  chez  nouv.-ne.  Arch,  de  phys.,  1894,  p.  472. — Mislawsky,  Centralbl.  /.  Wiss.,  1885. 
— W.-T.  Porter,  Journ.  of  Phys.,  1895,  p.  455. — Schiff,  Arch.  v.  Pflilger,  1870,  t.  IV, 
p.  225. — Speck,  Regulation  .   .  .,  Arch.  f.  Anat.  und  phys.,  1896,  p.  465. 

Phonation. — Duval  et  Raymond,  Arch,  de  phys.,  1879. — Frause,  Berlin.  Hin. 
Wochenschr.,  1890. — Radge,  Arch,  de  phys.,  1892,  p.  730. — Semon  et  Horsley,  Philos. 
Tran.  CLXXXI,  p.  187. — VuLPi.:Usr,  Lemons  svir  le  syst.  nerveux. 

Mimicry. — Bechterew,  Arch,  de  Pfliiger,  1887. — Brissaud,  Lemons  sur  les  maladies 
du  syst.  ner\'evix,  1895. 

Cough. — ^Koths,  Arch,  de  Pfliiger,  1874. — Schiff,  Recueil  de  memoires,  II,  p.  494. 
— VuLPiAX,  Arch,  de  phys.,  1882. 

Sneezing. — Luchsinger,  Arch,  de  Pfliiger,  1882. — S.^ndmann,  Arch,  de  Pfliiger. — 
Wertheimer  et  Surmont,  Biol.,  1888. 

Vomiting. — Hahnach,  Arch.  f.  Path,  und  Pharm. — Hla.sko,  Dissert.  Dorpat  ; 
Jahresb.  f.  Phys.,  1887.— Tumas,  Jahresb.  f.  Phys.,  1887. 

Co-ordination  of  the  reflexes ;  convulsions. — Biswanger,  Arch.  f.  Psych.  XIX. — 
Heubel,  Arch,  de  Pfliiger,  IX. — Luchsinger.  Arch,  de  Pfliiger,  1878  et  1880. — Luch- 
singer et  GuiLLEBE.\u,  Arch,  de  Pfliiger,  XXVIII  et  XXXIV. — Nothnagel,  Arch.  f. 
Anat.  und  Phys.,  IV. — Owsjanikow,  Berichte  d.  Ges.  d.  Wiss.  Leipzig,  1874. — Wert- 
HEiMER,  Journ.  de  Vanat.,  1886. 

Locomotion. — Fano,  Arch.  ital.  de  bioL,  1883. — Schrader,  Arch,  de  Pfliiger,  1887. — 
Steiner,  Jahresb.  f.  Phys.,  1885. — Tarchanoff,  Biol.,  1895. 

Blinking  of  the  eyelids. — Eckhard,  Centralbl.  f.  Phys.,  1895. — Exnee,  Arch,  de 
Pfliiger,  VIII. — Laborde,  Traite  de  phys. — Langendorff,  Arch,  de  Pfliiger,  1887. — 
Mendel,  Berl.  klin.  Wochenschr.,  1887. — Xickell,  Arch,  de  Pfliiger,  1888.  Vulpian, 
Sec.  phys.  coup.  Syst.  nerv. 

Mastication  and  suction. — Basch,  Succion,  Centralbl.  f.  Phys.,  1891. — Brown- 
Sequard,  BioL,  1849.- Gad,  Arch,  de  Pfliiger,  1891. 

Deglutition. — Meltzer,  Irradiation  .  .  .,  Arch.  f.  Anat.  und  Phy.'>.,  1883,  p.  209. — 
Steiner,  Schluck  .  .  .  und  Atiim  .  .  .  Arch.  f.  Anat.  und  Phys.,  1883,  p.  57. — Waller 
et  Prevost,  R(§flexe  deglutit..  Arch,  de  phys.,  1870,  pp.  185  et  343. 

Vaso-motor  centre. — Aducco,  Arch.  ital.  de  bioL,  XIV,  p.  37. — Dastre  et  Morat, 
Biol.,  Arch,  de  phys.  et  C.  R.  Acad:  sc,  1878  et  suiv. — Deganello,  Act.  temper  .  .  . 
Arch.  ital.  de  bioL,  1900,  t.  XXXIII,  p.  186.  Dittmar,  Bericht.  d.  Sachs.  Gesellsch., 
1871,  p.  135,  et  1873,  p.  449. — Owsjanikow  et  Tschiriew,  Bull.  Acad,  de  Saint-Petersb. 
et  Arch,  de  phys.,  1873,  p.  90. — Pierret,  Relation  entre  le  syst.  vaso-mot.  bulbe  et 
moelle,  C.  R.  Acad,  sc,  1882,  t.  XCXIV,  p.  225. — Sander  et  Kronecker,  Verbreitimg 
der  Gefassnerven  Centren,  Arch.  f.  Anat.  und  Phys.,  1882,  p.  422. — Schiff,  Unters.  z. 
Phys.  d.  Nervensyst.,  Francfort,  1855  ;  Recueil  de  memoires,  II,  578. — Stefani,  Act. 
temperat..  Arch.  ital.  de  biol.,  1895,  t.  XXIV,  p.  424. — Vulpian,  C.  R.  Acad,  sc,  1874, 
t.  LXXVIII,  p.  472. 

Dilatation  of  the  pupil. — Chauveau,  Journ.  de  la  phys.,  1861. — Franc, oisFranck, 
Trav.  labor,  de  Marey. — Gruenh.\gen,  Arch,  de  Pfliiger,  XL. — Gruenhagen  et  Cohn, 
Jahresb.  f.  Phys.,  1884. — Hensen  et  Vcelkers,  Arch.  f.  Ophtalm.,  1878,  XXIV.- — Kowa- 
lesky,  Arch.  slav.  de  biol.,  I,  p.  92. — Luchsinger,  Arch,  de  Pfliiger,  XXII,  1880. — 
Salkowsky,  Zeitsch.  f.  rat.  Med.,  1867. — Schiff,  Phys.  d.  Nervensyst.,  1858. 

Sudoriparous  secretion. — Fredericq,  Arch,  de  biol.,  1882. — Luchsinger,  Arch,  de 
Pfliiger.  XVI. — Xawrocki,  Centralbl.   Wiss.,  1879. 

Biliary  secretion. — Heidenhain,  Herman's  Handbuch. — Vulpian,  Biol.,   1861. 
Lachrymal  Secretion. — Seck,  Journ.  de  la  phys.,  1885. 

Digestive  secretions. — Heidenhain,  Secret,  pancreat..  Arch,  de  Pfliiger,  1875. 
Morat,  Biol.,  1894. — Pawlow,  Arch,  de  Pfliiger,  Suppl.,  1893. — Pawlow  et  Schumova 
Sim.anowskaja,  Centralbl.  f.  Phys.,  III. 

Diabetic  juncture. — Cl.  Bernard,  Lemons  sur  la  physiol.  exper.,  1855. — Chauveau 
et  Kauf3i.\nn,  Biol.,  1893. — Cyon  et  Aladoff,  Bull.  Acad,  des  sc  de  Saint-Petersb. 
1871. — Hedon,  Piqure  apres  extirp.  du  pancreas.  Arch,  de  phys.,  1894,  p.  269. — Kauf- 
MANN,  C.  R.  Acad,  sc,  1894,  t.  CXVIII,  p.  894  :  Arch,  de  phys.,  1895.— Kuhne,  Got- 
tinger  Nachricht,  1856. — Schiff,  Journ.  de  Vanat.,  1866. — Spalitta,  Polyurie,  Sicilia 
medica,  1889. — Vulpian,  Vaso-moteurs. 

Functional  associations  of  the  bulbar  centres. — Brown-Sequard  Journ.  de  la  phys., 
1858. — Burdon-Sanderson,  Handbook  of  Phys.,  1873,  p.  315. — L.  Fredericq,  C.  R. 
Acad,  sc,  1882. — Hering,  Sitz.  Acad.  Wien,  1869. — Knoll,  Sitz.  Acad.  Wien,  1885. — 
Meltzer,  Arch,  de  Pfliiger,  1883. — Steiner,  Arch,  de  Pfliiger,  1883. — Wertheimer  et 
Meyer,  Arch,  de  phys.,  1889  et  1890. 


372  SYSTEMATIC    FUNCTIONS 


CHAPTER    IV 

SUPERIOR    SYSTEMATIZATIONS 

Both  morphologically  and  functionally,  the  nervous  structures  situated 
above  the  pons,  the  cerebellum  and  the  brain,  properly  so  called,  form 
very  important  and  highly  differentiated  systems.  These  systems  are 
not  in  direct  communication  with  the  peripheral  organs,  some  of  which 
are  receptive  of  impressions  and  others  executive  of  functions.  They 
receive  impulses  which  have  already  been  transformed  and  mutually 
associated  in  the  spinal  cord  and  the  medulla  oblongata  ;  they  also 
act  on  motor  associations  belonging  to  these  two  organs,  which  are 
organized  internally  for  the  jDcrformance  of  definite  acts  or  movements, 
whose  realization  they  have  the  power  of  determining.  They  are  still 
less  the  ef[icient  cause  of  movement  than  are  the  inferior  systems  which 
they  govern  ;  but  are  to  a  greater  degree  than  these  a  directing  factor 
in  the  transformations  of  energy  which  take  place  in  the  course  of  the 
performance  of  functions.  By  their  hierarchical  situation  above  the 
preceding,  and  by  their  internal  organization,  they  bring  about  those 
syntheses  which,  in  the  order  as  much  of  sensation  as  of  movement, 
produce  unity  of  the  functions,  and  by  the  mutual  dependence  and 
harmonious  concordance  of  these  latter,  the  unity  of  the  ego. 

A.   ORIENTATION  AND  EQUILIBRATION  ;   THE 
CEREBELLUM 

To  the  spinal  cord  and  the  medulla  oblongata,  which  are  in  direct 
relation  with  the  sensory  and  muscular  organs,  and  which  associate 
them  in  simple  acts,  sensitivo-motor  cycles  are  superposed,  repre- 
senting elaborated  systems. 

These  are  more  or  less  multiphed  according  to  the  degree  of  organiza- 
tion of  the  animal  under  consideration,  and  are  variously  differentiated 
according  to  the  nature  of  its  functions.  They  correspond  to  a  division 
of  the  internal  work  of  the  nervous  system. 

They  represent  special  modalities  of  the  senso-motricity  of  which  the 
reflex  bulbo-meduUary  arc  sjrmbolizes  the  simplest  form.  United  by 
the  latter  to  the  organs  receptive  of  impulses  and  executive  of  move- 
ments, they  adapt  the  bulbo-meduUary  system  to  determinate  func- 
tions which  differ  according  to  each  of  them.  In  this  way  these 
superior  systems  employ  the  inferior  ones  to  perform  their  func- 
tions ;  for  this  purpose  they  have  only  to  utihze  the  elementary  associa- 


SUPERIOR  SYSTEMATIZATIOXS  373 

tions  prepared  by  the  organization  belonging  to  these  simple  systems, 
by  incorporating  them  with  the  more  extended  and  more  specific 
associations  which  they  bring  into  being.  In  this  way  these  inferior 
systems  execute  acts  whose  complexity  and  variety  go  far  beyond  any 
of  which  they  are  capable  when  reduced  to  a  state  of  isolation. 

The  cerebellum  is  a  superior  system  of  this  nature.  It  has  special 
relations  both  with  sensation  and  motion.  Its  principal  stimuli  are 
derived  from  organs  themselves  of  a  special  nature  (semi-circular 
canals),  as  well  as  from  touch  and  vision.  It  conveys  the  impulse  in 
its  turn  to  the  muscles  (principally  to  those  of  the  life  of  relation), 
whose  tonic  activity  it  maintains,  at  the  same  time  harmonizing  their 
contractions,  with  the  aim  in  view  of  maintaining  the  attitude  of 
the  body  in  the  upright  position  and  in  walking. 

Historical  —  Tlie  siDecial  situation  and  tlie  external  configvu-ation  of  the  cere- 
bellum have  given  rise  to  a  certain  number  of  hj'potheses  concerning  its  functions 
which  it  is  scarcely  necessary  to  recall.  Willis  considered  it  to  be  the  centre  of 
organic  fmictions.  Rolando  compared  its  layers  to  the  couples  of  a  galvanic 
battery  and  regarded  it  as  a  generator  of  motor  force.  Gall  located  here  the 
inclination  for  physical  love,  and  the  instinct  of  the  propagation  of  the  species. 

The  experimental  and  analytical  study  of  its  fvmctions  begins  ^\^th  Flourens 
in  1824.  The  researches  of  this  author  have  been  made  on  a  large  number  of 
species,  princii:)ally  on  birds  and  esi^ecially  on  the  pigeon,  and  also  on  mammals. 
His  animals  ha^e  sm-vived,  and  so  permitted  him  to  observe  the  effects  con- 
secutixe  to  ablation.  His  experiments,  being  very  methodically  carried  out, 
have  establislied  very  definite  facts  which,  though  elaborated  by  his  successors, 
M^ill  eontinvie  to  form  the  basis  of  all  om-  knowledge  with  regard  to  the  functions 
of  the  cerebelhun. 

Function  of  motor  co-ordination.— He  distinctly  states  that,  after  ablation  of 
the  cerebellum,  sensation,  intelligence  and  will  are  preserved  :  the  animal  has 
not  lost  the  inclination  for  movement,  but  this,  from  being  previously  coherent 
and  ordinate,  has  now  become  disordered,  and  no  longer  realizes  the  end  which 
its  will  or  instinct  has  in  view.  This  disorder  is  the  greater  when  the  more  co- 
ordinate movements  are  under  consideration  ;  in  the  bird  which  flies,  flight 
would  be  of  this  niuuber  ;  in  the  case  of  birds  which  walk  and  swim,  it  would  be 
walking  and  swimming.  The  movements  of  locomotion  are  lost,  but  those  of 
conservation  persist.  If  the  cerebellum  is  removed  in  successive  slices,  layer  by 
layer,  this  w^nt  of  harmonj-  goes  on  increasing  ;  once  the  organ  is  removed,  the 
animal  is  incapable  of  holding  itself  upright  or  of  walking. 

From  these  faets  Flourens  derives  evidence  of  the  existence  of  a  function  of 
co-ordination  of  movements  (voliuitary)  whose  seat  is  in  the  cerebellum.  To 
attribute  a  function  of  co-ordination  to  this  organ  alone  is  no  doubt  to  go  beyond 
the  demonstrated  facts,  and  even  the  intention  of  the  author  ;  for  he  himself 
remarks  that  nutrition  remains  co-ordinated,  and  on  the  other  hand  we  know 
that  co-ordination  of  movements  of  locomotion  may  be  destroyed  by  lesions  of 
organs  other  than  the  cerebellum  (locomotor  ataxy  of  tabetic  origin  ;  lesion  of 
the  roots  and  the  columns  of  the  spinal  cord). 

In  the  adaptation  of  muscular  movements  to  a  definite  function,  like  the  main- 
tenance of  the  ui^right  jDOsition  or  walking,  the  part  played  by  the  cerebellum  is 
not  exclusive,  but  is  nevertheless  essential,  and  for  want  of  a  special  term  which 


374  SYSTEMATIC    FUNCTIONS 

is  still  lacking  to  define  tliis  role,  it  has  been  found  necessary  for  the  sake  of 
concentration  to  adopt  one  having  a  more  general  value. 

The  experiments  of  Bouillaud,  Lussana,  Wagner,  Vidi^ian  and  many  others 
have  led  these  authors  to  the  demonstration  of  facts  which,  as  a  whole,  differ 
but  little  from  those  established  by  Flom-ens,  and  to  conclusions  resembling  his. 
Lussana,  in  the  interpretation  he  gives  to  these  facts,  considers  the  cerebelliim 
as  being  the  organ  of  the  muscular  sense.  The  localization  attributed  at  the 
present  day  to  the  muscular  sense  is  quite  different  ;  it  is  considered  to  be  situ- 
ated in  the  cortex  of  the  central  convolutions  of  the  brain,  in  company  with  the 
sense  of  touch,  of  which  it  is  a  dependent  form.  So  far  as  the  muscular  sense 
lies  in  the  more  or  less  distinct  consciousness  wliicli  we  have  of  ovu"  muscles  and 
of  their  state  of  contraction,  this  localization  is  not  controvertible  ;  but  it  miist 
not  be  forgotten  that,  just  as  motricity  has  very  variovis  forms  and  expressions 
in  the  brain  and  the  cerebelliim,  so  also  may  sensation  affect  different  modalities 
in  the  nervous  organs  which  the  centripetal  imjoulse  passes  through  before  arriv- 
ing at  the  cerebral  cortex.  The  cerebellum  receives  from  the  muscles,  and  at 
the  same  time  from  the  organs  of  touch,  and  of  several  other  senses,  impulses 
wliich  are  reflected  by  it  under  the  form  of  movement,  and  so  far  it  may  be  con- 
sidered as  an  organ  of  sensibility,  but  of  a  sensibility  which  is  not  exclusively 
muscular. 

The  experiments  of  Majendie,  Longet,  and  Schiff  were  directed  more 
particularly  to  the  cerebellar  peduncles  and  to  the  movements  of  rotation 
resulting  from  their  section. 

Function  of  equilibrium. —  Since  Flourens,  the  most  important  work  on  the 
functions  of  the  cerebellum  is  due  to  Luciani  (1884-1891).  The  length  of  time 
his  animals  have  sui'vived  the  operation,  the  detailed  study  of  s^^Tlptom3  and 
their  evolution,  the  simultaneous  study  of  structixral  anatomy  unite  in  giving 
great  interest  to  his  work.  Ferrier  has  also  largelj^  contributed  to  ovu"  knowledge 
of  the  functions  of  the  cerebelliim  by  the  method  of  localized  stimulations  which 
he  has  applied  to  this  organ.  He  substitutes  electrical  stimulation  for  the 
mechanical  or  chemical  excitations  emploj-ed  by  Weir-Mitchell  and  Xothnagel. 
Luciani  carefully  distinguishes  between  the  symj^toms  due  to  irritation,  those 
due  to  deficiency,  and  those  of  compensation  or  of  supplement,  wliich  succeed 
each  other,  and  sometimes  co-exist  in  the  intermediate  phases.  Following 
Leven,  Ollivier,  Luys,  and  Weir-Mitchell,  lie  draws  attention  to  the  diminution 
of  muscular  force  which  is  displayed  after  the  period  of  irritation.  The  contrac- 
tions are  feebler  on  the  side  corresponding  to  the  lesion  ;  this  is  what  he  has  named 
asthenia.  The  muscular  tone  is  diminished,  hence  arise  flexion  of  the  limbs  and 
frequent  falls  when  in  the  erect  position  :  atony.  There  are  also  tremors,  oscilla- 
tions and  titubation,  these  being  due  to  the  fact  of  the  nervovis  impulses  not 
following  each  other  with  sufficient  rai^idity  :  this  is  astasia.  Nevertheless, 
Laborde  disputes  these  interi^retations,  and  prefers  to  them  the  explanation  of 
Flourens. 

From  these  facts,  Luciani  concludes  that  the  cerebellum  has  the  power  of 
augmenting  the  potential  energy  of  the  nervous  system  (sthenic,  tonic  and  static 
action)  :  this,  however,  is  taking  appearance  for  reality,  no  part  of  the  nervous 
system  being  capable  of  furnishing  potential  energy  to  any  nervous  or  non- 
nervous  organ,  but  only  having  the  jiower  of  causing  it  to  dispense  that  wliich 
comes  to  it  from  food  and  is  stored  uji  in  its  reserves. 

The  weakening  of  the  muscular  tone  following  the  destruction  of  the  cerebel- 
Imii  is,  nevertheless,  a  very  real  fact  and  has  been  proved  by  all  experiments 
undertaken  mider  the  same  conditions.  The  influence  possessed  by  the  cere- 
bellum of  maintaining  the  muscular  tonus  has,  according  to  Ewald,  its  principal 
starting  point  in  the  impulses  it  receives  from  the  vestibular  nerve  :    the  effects 


SUPERIOR  SYSTEMATIZATIONS 


375 


of  section  of  this  nerve  are  similar  to  those  cavised  by  destruction  of  the  cere- 
belhun. 

Trophic  influence. — Removal  of  the  cerebellum  causes  consecutive  degenera- 
tions of  various  kinds,  either  in  the  bundles  of  fibres  connecting  it  with  the  organs, 
or  in  the  muscles  or  even  the  skin  (Luciani).  These  distiirbances  of  nutrition 
obey  the  general  laws  regulating  the  appearance  and  progress  of  degenerations 
consecutive  to  nervous  lesions.  The  fibres  when  cut  in  their  course  undergo 
Wallerian  degeneration  ;  later,  secondary  atrophy  may  invade  the  nervous 
elements  or  the  organs  to  which  they  are  distributed. 

Comparative  axato:my. — The  cerebellum  is  present  in  all  vertebral  a  ;  its 
development  is  in  relation 


■"^% 


Fig.    150. — Cerebellum  of  the  dog. 

On  the  left,  posterior  and  superior  aspect  ;  on 
the  right,  right  external  aspect. 

1,  pyramid  of  the  middle  lobe  ;  2,  posterior  extremity  of 
the  superior  vermiform  process  ;  3,  its  anterior  extremity  ; 
4,  lateral  lobe  and  its  posterior-superior  lobule  ;  5,  flocculus 
(after  Ferrier). 


it   has 


to  the  complication  of  the 
conditions  which  ensure 
equilibrium  in  these  ani- 
mals. At  least  this  is 
wliat  stands  out  m  o  s  t 
markedly  from  a  summary 
study  of  these  conditions 
and  of  the  comparative 
development  of  the  organ 
in  question  (Thomas). 

Reptiles. —  The  c  e  r  e  - 
bellrun  can  hardly  be  said 
to  be  present  in  reptiles, 
and  is  reduced  to  a  trans- 
verse layer  lying  across  the 

fourth  ventricle  (adder,  toad,  frog,  lizard,  tortoise,  terrestrial  salamander  .  .  .), 
in  the  turtle  it  forms  a  globular  mass  larger  than  one  of  the  optic  lobes— in 
the  crocodile  it  displays  several  folds,  and  two  lateral  appendices  are  ob- 
served (Leuret). 

Fishes. —  In  fishes  it  is  almosfas  reduced  in  size  as  in  reptiles  (Serres)  ; 
the  form  of  an  elongated 
layer  adhering  in  front, 
free  at  the  back,  attached 
to  the  sides  of  the  spinal 
cord.  In  the  dog-fish  and 
the  shark  it  possesses  two 
lateral  appendices. 

In  those  animals  which 
almost  exclusively  crawl 
on  the  ground  or  swim  in 
the  water,  vthe  conditions 
of  equilibrium  are  simple. 
The  same  cannot  be  said 
as  regards  the  two  following  classes. 

Birds. —  In  birds  the  cerebellum  assumes  a  considerable  development  ;  it  is 
formed  of  a  single  median  lobe  presenting  from  ten  to  twenty  parallel  layers 
(Leuret).  It  is  only  in  some  kinds  of  birds  that  the  median  lobe  is  laterally 
enlarged  (notably  in  the  pigeon,  the  ostrich,  the  stork,  etc.).  According  to 
Serres,  this  de\-elopment  is  in  agreement  with  the  greater  strength  of  the  wings, 
and  superior  aptitude  for  flight.  In  birds,  the  fom'th  ventricle  is  prolonged  into 
the  cerebelliun  (ventricle  of  Malacarne).  Thomas  has  observed  that,  contrary 
to  the  opinion  of  Serres,  their  cerebellum  possess  four  nuclei,  two  larger  lateral 
ones,  probably  corresponding  to  the  ciliary  bodies  (corpora  dentata),  and  two 


on  the 


Fig.    151. — Cerebellum  of  the  monkey. 

On  the  left,  superior  and  posterior  aspect 
right,  left  lateral  aspect. 

3,  superior  vermiform  process,  behind  which  the  middle 
lobe  with  its  pyramid  is  seen  ;  4,  lateral  lobes  witli  their 
semi-lunar  lobule  ;    5,  flocculus  (after  Ferrier). 


376  SYSTEMATIC    FUNCTIONS 

smaller  median,  separated  by  the  ventricle  of  Malacarne,  which  represent  the 
nucleus  of  the  roof.  This  author  is  convinced  that  the  structure  of  the  cere- 
bellum is  essentially  the  same  in  reptiles  and  birds  as  in  mammals. 

Mammals.- —  In  mammals  the  lateral  masses,  hardly  indicated  in  birds,  assume 
a  relatively  considerable  v^olume.  The  number  of  the  layers  is  variable  :  9 
in  the  bat,  12  in  the  rat,  32  in  the  rabbit,  66  in  the  sheep,  75  in  the  ox,  175  in 
the  horse.  Still  reduced  in  the  rodents,  the  lateral  lobes  undergo  pro- 
gressive development  in  ruminating  animals,  in  the  solipedia,  carnivora,  and 
especially  in  the  dolphin  and  the  monkey.  While  the  median  lobe  is  inversely 
proportionate  to  the  cerebral  hemispheres,  the  lateral  lobes  are  on  the  con- 
trary directly  proportionate  to  them.  The  functions  of  the  first  should  then, 
according  to  Notlinagel,  differ  from  those  of  the  second,  it  being  iinderstood 
that  no  attempt  is  made  to  define  the  nature  of  either  one  or  the  other.  With 
regard  to  this  the  opinion  of  Serres  seems  nearest  the  truth,  and  the  cerebellar 
hemispheres  should  by  preference  take  part  in  acts  of  a  voluntary  nature 
(Thomas). 

1.     Conditions  of  equilibrium 

The  conditions  of  equilibrium  have  been  analyzed  by  authors  who 
have  studied  this  function  experimentally,  and  especially  by  Thomas. 
The  attitude  of  the  human  body  and  of  that  of  animals  in  the  upright 
position  being  assumed,  equilibrium  is  effected,  as  we  know,  when 
the  axis  of  the  ceritre  of  gravity  falls  within  the  polygon  which  represents 
the  base  of  support.  The  body  is  then  subjected  to  two  equal  and  con- 
trary forces,  one  of  which  (weight)  is  represented  by  the  axis  indicated, 
the  other  (resisting  force)  by  the  supports  (limbs  of  the  animal)  resting 
on  the  ground. 

1 71  the  upright  attitude. — These  supports  are  articulated  systems 
which,  by  contraction  of  certain  of  the  muscles  (extensors),  the  animal 
can  cause  to  become  rigid,  and  which  he  can  also  solidarize  with  the 
trunk  by  the  contraction  of  other  muscles.  The  trunk  itself,  with  its 
superior  prolongation  (the  head),  is  a  system  formed  of  mobile  portions, 
which  become  rigid  by  contraction  of  the  muscles  inserted  therein. 
This  relative  rigidity  is  thus  obtained  by  the  tonic  action  of  a  large 
number  of  muscles,  whose  efforts  are  antagonistic  in  numerous  direc- 
tions. The  antagonism  exists  from  one  side  to  the  other  for  muscles 
of  the  same  name  ;  and  from  front  to  back  for  the  posterior  and  an- 
terior limbs  of  animals  ;  it  also  exists  for  the  muscles  of  each  segment 
of  the  skeleton  considered  in  an  isolated  manner  (extensors,  flexors, 
adductors,  abductors,  rotators,  in  one  or  the  other  direction,  etc.). 
Preservation  of  equilibrium  when  standing  still  implies,  as  is  obvious,  a 
contraction,  co-ordinated  in  extent  and  direction,  of  almost  all  the  muscles 
of  the  body. 

In  walking. — In  walking  the  supports  of  the  body  undergo  limita- 
tions and  alterations  as  they  succeed  each  other  periodically,  and  at 
the  same  time  they  are  carried,  one  in  front  of  the  other,  in  a  definite 


SUPERIOR  SYSTE:\IATIZATI0NS  377 

direction.  In  man  these  movements  are  produced  alternately  on  one 
or  the  other  foot  ;  in  quadrupeds  they  are  limited  to  three,  then  to 
two  limbs,  in  a  diagonal  direction  (ordinary  walk,  trot),  or  in  an  antero- 
posterior direction  (amble).  Equilibrium,  threatened  every  moment, 
is  re-established  by  compensating  changes  in  the  attitude  of  other  parts 
of  the  body  ;  these  changes  having  for  their  aim  and  object  the  con- 
tinued retention  of  the  axis  of  the  centre  of  gravity  in  the  more  or  less 
restricted  area  of  the  base  of  support  (lateral  oscillations  of  the  trunk, 
rotation  in  an  opposite  direction  of  the  pelvis  and  the  shoulders  ; 
antagonistic  oscillations  of  the  arm  and  of  the  leg  of  the  same  side,  etc.). 

Analogous  compensations  appear  in  all  acts  of  a  similar  nature  which 
require,  as  the  essential  condition  of  their  performance,  the  preserva- 
tion of  equilibrium  (running,  jumping,  etc.).  All  these  acts  expend  a 
certain  amount  of  muscular  energy,  which  is  employed  in  overcoming 
resistances  and  effecting  movement  in  a  definite  direction  ;  but, 
further,  another  expenditure  is  demanded  from  the  muscular  tissue  as 
a  whole,  in  order  to  prevent  falling  ;  this  expenditure  continues  in  the 
upright  position,  and  onh^  ceases  during  the  total  decubitus  of  the 
body  in  man  or  in  animals  when  extended  on  a  plane  surface. 

1.  Reciprocal  relationship  between  the  motor  effect  and  the  sensory 
stimulation. — In  order  that  the  muscles  of  the  body,  by  their  aggre- 
gate contraction,  may  bring  about  these  compensations,  it  is  necessary 
that  there  should  be  developed  through  the  nervous  system  a  cycle  of 
stimulation  in  virtue  of  which  the  individual  static  contractions  of  all 
those  muscles  are  regulated  hy  the  effect  obtained,  ready  to  be  reinforced 
in  the  direction  of  falling  and  to  be  moderated  in  the  opposite  direction. 
This,  further,  is  the  usual  manner  in  which  all  the  equihbria  in  the 
organism  are  effected,  being,  as  they  all  are,  of  a  mobile  nature  (circula- 
tion, respiration,  calorification,  composition  of  the  blood,  the  humours, 
the  organs,  etc.).  This  is  also  a  very  general  function  of  the  nervous 
system,  and  the  end  aimed  at  by  its  organization  is,  as  it  were,  the 
insurance  of  equihbrium  in  the  animal  economy.  There  is  hardly  any 
reflex  system  whose  function  does  not  participate  in  this. 

The  co-ordination  of  movements,  of  acts  of  whatever  nature,  is  not 
then  a  specific  function  of  a  definite  system  ;  but  the  equilibrium  of  our 
bodies  in  standing  and  in  progression  is  a  special  case  of  co-ordination 
of  movements,  and,  as  such,  possesses  in  the  cerebellum  its  most 
differentiated  representation. 

It  must,  however,  be  understood  that  this  differentiation  does  not 
imply  isolation  ;  the  cerebellum  is  a  nervous  organ  superposed  on 
inferior  systems  (spinal  cord),  in  which  motion  is  realized  and  co- 
ordinating action  sketched  out  ;  further,  it  is  united  to  superior  systems 


378  SYSTEMATIC    FUNCTIONS 

which  govern  it  and  aid  or  supplement  it,  when  its  own  action  is  wanting 
(optic  thalamus,  corpus  striatum,  cerebral  cortex). 

2.  Sense  of  equilibrium. — We  possess  a  sense  of  equilibrium  which  is 
a  modality  of  what  is  still  called  sense  of  orientation,  or  se7we  of  space. 
The  word  sense  has  in  physiological  language  a  very  special  signification, 
but  it  has  also  a  general  meaning,  and  this  is  the  case  here.  A  sense, 
properly  so  called,  is  defined,  on  the  one  hand,  by  the  specific  nature 
of  the  stimulus  acting  upon  it  (luminous  or  sonorous  vibration,  etc.) ; 
on  the  other,  by  the  equally  specific  nature  of  the  resulting  sensation 
(visual  or  auditive,  etc.). 

We  know  of  no  stimulus  or  specific  energy  answering  to  the  sense  of 
space.  It  has  been  well  said  that  the  ideas  of  direction  in  space  come 
to  us  by  means  of  a  special  apparatus,  the  semi-circular  canals,  and  it 
has  been  proved  experimentally  that  the  destruction  of  these  canals 
brings  about  serious  disturbances  of  equiHbrium  ;  but  experiment  has 
also  proved  that,  after  lesion  of  these  canals,  this  function  may  be 
re-established.  Section  of  the  two  nerves  of  the  eighth  pair  leads  to 
disturbances  of  hearing  (cochlear  nerve),  and  also  to  those  of  equilibrium 
(vestibular  nerve)  ;  after  this  mutilation,  hearing  is  lost  for  ever  ; 
equilibrium,  on  the  contrary,  becomes  possible  after  some  weeks  have 
elapsed.  Although  the  latter  may  receive  its  principal  guidance  from 
the  semi-circular  canals,  it  seems  as  if  it  also  collects  it  elsewhere. 
Tactile,  muscular,  articular  and  visual  sensations  all  contribute  to  the 
realization  of  equilibrium.  Equilibration  is  not  a  specific  sense,  but  a 
function  which  appeals  to  several  senses  ;  there  are  as  many  ways  of 
compromising  it  as  there  are  senses  taking  part  in  it  ;  the  deficiency 
of  each  of  these  may  be  more  or  less  covered  up  by  the  supplementing 
and  compensating  action  of  the  subsisting  senses  (Lugaro). 

Not  only  do  we  find  at  the  periphery  neither  a  specific  stimulus  nor 
an  exclusive  organ  adapted  to  the  sense  of  space,  but  the  impulses 
furnished  by  the  semi-circular  canals  do  not  appear  to  reach  the  con- 
sciousness. Collected  by  a  series  of  nuclei  (nuclei  of  the  roof,  of  Deiters 
and  Bechterew,  dorsal,  descending),  the  impulses  transmitted  by  the 
vestibular  nerve  are  directed  towards  the  cerebellum,  the  motor  nuclei 
of  the  bulb  (oculo-motors),  and  the  superior  portion  of  the  spinal  cord  ; 
but  no  distinctly  traced  path  for  them  as  concerns  the  cerebral  cortex 
is  known.  The  fibres,  doubtless  but  few  in  number,  representing  this 
path  do  not  proceed  to  the  auditory  area,  but  rather  to  that  of  touch. 

These  impulses  fall  into  a  reflex  system  which  regulates  the  position 
of  the  eyes,  of  the  head,  and  of  the  trunk,  and  thus  governs  more  or 
less  directly  the  function  of  orientation  and  equilibrium,  by  an  un- 
conscious adaptation  of  the  contractions  of  the  muscles  to  this  function. 


SUPERIOR  SYSTEMATIZATIONS  379 

Such  of  these  impulses  as  reach  the  cerebellum  act  by  means  of  this 
organ  in  quite  as  unconscious  a  manner  on  the  muscular  tonus,  so  as 
constantly  to  compensate  for  displacements  (in  standing  or  progression) 
by  which  the  equilibrium  might  be  jeopardized. 

3.  Automatic  action. — Every  reflex  cycle  implies  association  of  sensa- 
tion to  movement  ;  and,  further,  we  see  that  this  association  is  adapted 
to  a  particular  end.  Our  conscious  voluntary  acts  come  under  this 
definition.  Equilibrium  in  standing  or  in  progression  may  be  an  act 
of  this  nature  in  an  individual  attacked  by  paralysis,  or  in  whom  the 
cerebellum  is  destroyed,  who  can  supplement  the  absent  mechanism 
by  efforts  of  reason  ;  in  the  infant  who  learns  to  hold  himself  upright 
and  to  walk  ;  even  in  the  individual  who,  in  order  to  accomplish  a 
difficult  equilibrium,  puts  his  brain  to  work  so  as  to  assist  his  cerebellum. 
But  these  are  all  cerebral  acts  ;  the  action  of  the  cerebellum  is  auto- 
matic, that  is  to  say,  without  participation  of  distinct  consciousness  or 
personal  will.  In  being  constituted  a  functional  differentiated  sj^stem, 
the  cerebellum  has  certainly  acquired  special  aptitudes,  from  the  point 
of  view  of  sensibility  as  well  as  from  that  of  motricity  ;  only,  being 
lost  in  the  domain  of  unconsciousness,  the  former  elude  our  observation 
even  more  completely  than  do  the  latter. 

4.  Sources  of  stimulation. — Thus  we  see  that,  in  order  to  bring  about 
the  motor  effect  by  which  equilibrium  is  ensured,  the  cerebellum  gathers 
impulses  from  several  senses.  In  the  first  place  it  receives  them  through 
the  vestibular  nerve  from  a  special  apparatus  annexed  to  the  sense  of 
hearing  :  the  semi-circular  canals.  Flourens  was  the  first  to  observe 
the  extremely  strict  functional  relationship  existing  between  this 
apparatus  and  the  cerebellum.  Lesions  of  the  semi-circular  canals 
give  rise  to  the  same  disturbances  as  do  those  of  the  cerebellum  ;  accord- 
ing as  to  whether  one  or  the  other  canal  be  injured,  disorders  of  equili- 
brium, rotation  in  one  direction  or  the  other,  or  in  different  directions, 
are  produced,  just  as  in  removal  of  the  unsymmetrical  portions  of  the 
cerebellum.  It  is  thence  that  the  individual  obtains  his  images  of  the 
cephalic  attitude,  which  are  due  to  the  analyses  effected  by  the  ampullary 
nerve  of  the  internal  ear. 

The  cerebellum,  on  the  other  hand,  receives  impulses  from  two  im- 
portant senses,  the  visual  and  the  tactile  sense  ;  from  the  latter  it  re- 
ceives both  superficial  and  deep  impulses,  especially  deep  ones  coming 
to  it  from  the  muscles  and  the  articulations  themselves.  These  furnish 
the  individual  with  the  images  of  his  segmentary  attitudes.  Thus  in 
man,  when  in  the  upright  position,  the  reciprocal  attitude  of  the  foot 
and  the  leg  play  an  important  part  (and  especially  when  the  ampullary 
images  are  disturbed).     From  this  results  what  might  be  called  a  new 


380  SYSTEMATIC    FUNCTIONS 

sense,  taking  cognizance  of  the  oscillations  of  the  leg  on  the  foot  and 
permitting  the  tibio-tarsal  muscles  to  accomplish  definite  efforts  for 
the  correction  of  errors  of  equilibrium  directly  these  show  a  tendency 
to  arise  (Bonnier). 

5.  Progress  of  the  impulses. — The  cerebellum,  like  the  spinal  cord 
and  the  bulb,  is  capable  of  reflecting  the  impulses  coming  to  it  from 
the  organs  of  sense  on  those  of  movement  ;  it  is  in  fact  attached  to  the 
spinal  cord  by  two  kinds  of  fibres,  the  first  ascending  (direct  cerebellar 
tract),  and  the  second  descending,  which  it  associates  by  its  grey  sub- 
stance, having  special  functions  in  view  (equilibrium),  which  may  be 
exercised  without  the  intervention  of  consciousness.  But,  further,  and 
in  this  once  more  resembling  the  s^jinal  cord  and  the  medulla  oblongata, 
the  cerebellum  is  located  in  the  course  of  a  general  current  of  impulses, 
which  passes  through  the  brain.  In  fact,  we  see  it  connected  with  the 
optic  thalamus  and  the  cortex  by  the  superior  cerebellar  peduncles, 
which  allow  of  its  exchanging  impulses  with  these  organs. 

The  sensory  impulses  of  bulbo-medullary  origin  may  then  go  beyond 
it,  and  may  reach  in  the  brain  :  (1)  the  optic  thalamus,  (2)  the 
cortex.  From  these  two  collections  of  grey  matter  we  know  that  they 
may  again  descend  to  the  grey  bulbo-medullary  axis  by  the  crura  cerebri : 
this  seems  to  be  the  most  probable  path.  We  have  no  reason  to  think 
that  this  path  is  an  exclusive  one,  and  on  the  other  hand,  we  know  that 
it  is  not  simple.  The  fibres  of  the  pyramidal  tract  (that  is  to  say, 
motor)  descending  from  the  cortex  give  oft"  collaterals  when  passing 
through  the  pons,  which  become  connected  with  the  fibres  of  the  middle 
peduncle,  and  proceed  to  the  cerebellum.  This  distribution  of  descend- 
ing impulses  on  the  path  of  the  same  fibre  which  furnishes  them  in  this 
way  both  to  the  cerebellum  and  the  grey  bulbo-medullary  axis  simul- 
taneously, is  a  detail  of  structure  the  part  played  by  which  still  remains 
unexplained.  On  the  other  hand,  the  crura  cerebri  contain  ascending 
elements  (that  is  to  say,  sensory)  which  proceed  to  the  optic  thalamus 
and  to  the  cortex  (thalamic  and  cortical  portion  of  the  fillet)  {ruhan  de 
Reil)  ;  and  from  these  areas  of  grey  matter  the  impulses  find  paths 
for  returning  to  the  brain  by  the  superior  peduncles  of  the  cerebellum. 
From  the  cerebellum  they  have  once  more  efferent  paths  to  bring  them 
back  to  the  spinal  cord  by  the  inferior  and  middle  peduncles. 

Anatomy,  by  its  special  methods,  shows  us  that  the  impulse  may  be 
propagated  in  both  directions  (afferent  and  efferent  fibres),  in  each  of 
the  three  peduncles  which  on  both  sides  attach  the  cerebellum  to  the 
adjacent  masses  both  above  and  below.  From  this  results  the  possi- 
bility of  the  existence  of  cycles  whose  general  direction  varies  some- 
times in  one  way,  sometimes  in  the  other,  and  which  may  give  rise  to 


SUPERIOR  SYSTEMATIZATIONS 


381 


Sup.  pel. 


Cort.  p'jn.  path. 


currents  capable  of  being  inverted  or  even  of  co-existing,  according  to 
circumstances,  since  conducting  elements,  at  once  opposed  and  inde- 
pendent, exist  in  each  of  the  three  peduncles. 

The  cerebellum  and  reflex  movements. — The  cerebellmn  maintains  equilibrimn 
We  recognize  that  it  exerts  an  action  on  the  muscular  tone  ;  and,  in  the  same 
order  of  ideas,  we 

also    attribute   to  i.ei  nuc'.eus 

it  a  part  in  the 
execution  of  a 
great  number  of 
reflex  movements 
wliich,  according 
to  some  authors, 
woiild  withoirt  it 
become  i  m  p  o  s  - 
sible,  at  least  in 
man  (Bastian). 
Certain  p  a  t  h  o  - 
logical  facts  have 
been  appealed  to 
in  favour  of  tliis 
influence  of  the 
cerebellum  on  re- 
flex actions. 

As  a  result  of 
compression,  d  e- 
struction  and  in- 
t  e  r  r  u  p  t  i  o  n  of 
continuitj'  of  the 
dorsal  spinal  cord, 
the  tendon  r  e- 
flexeswill  be  seen 
to  disappear 
(flaccid  paralysis); 
following  injxu'ies 
which  involve  the 
cerebral  h  e  m  i - 
sphere  or  its  white 
tracts  above    the 


lid.  pel. 


Pont.  S. 


Inf.  pei. 


Goll  aivl  Burdach 


Col.  of  Clarke 


Ant,    CO  mil. 


Fig. 


152. — Diagram  of  the  connexions  between  the   cerebellum, 
the  bram,  the  pons  and  the  spinal  cord  (Charpy). 


pons,  an  exagger- 
ation of  tlrese  re- 
flexes  will   be  observable    (posthemiplegic  contract/ion).     Van  Gehuchten  ex- 
plains these  clinical  differences  by  the  varying  site  of  the  lesion,  which,  in  the 
case  of  medullary  injmy,  suppresses  the  influence  of  the  cerebellum,  and  in  that 
of  cerebral  lesion  allows  of  its  persistence. 

Yet  more,  in  this  latter  case  these  reflexes  are  often  exaggerated  :  thus  the 
brain,  in  addition  to  the  motor  or  exciting  action  that  it  certainly  exercises  on 
the  spinal  cord  (cortico-spinal  fibres),  also  jjossesses  another,  of  inhibitory  natiu-e, 
which  affects  the  cerebelhmi  (cortico-ponto-cerebellar  fibres). 

The  disappearance  of  this  arresting  influence,  in  the  case  of  cerebral  destruc- 
tion would,  in  spite  of  the  deficiency  of  cerebral  exciting  action,  still  be  sufficient 
to  give  to  the  cerebellum  a  preponderating  influence  in  the  excitation  of  the 
spinal  cord  by  its  descending  fibres  (cerebellar-spinal). 


382 


SYSTEMATIC    FUNCTIONS 


Red  nucleus. — Van  Geliucliten,  on  the  other  liand,  draws  a  distinction  between 
tile  tendon  reflexes  (having  for  starting  j^oint  mechanical  stimulation  of  a  tendon) 
and  cutaneous  reflexes  (produced  by  irritation  of  the  skin).  According  to  this 
author,  the  latter  are  developed  in  an  arch  comialeted  in  the  cortex,  and  they 
depend  on  the  integrity  of  the  corticospinal  path  ;  the  former  are  developed  in 
an  arc  completed  in  the  red  nucleus,  they  are  connected  with  the  integrity  of 
the  rubrospinal  jsath  ;  on  the  tendon  reflexes  the  eortico-spinal  path  exercises 
an  influence  which  is  for  the  most  jDart  inhibitory. 

Medullary  reflexes. — After  section  of  the  spinal  cord  (for  example,  in  the  dorsal 
region),  the  possibility  of  eliciting  reflex  movements  of  the  inferior  limbs  will  not 
have  entirely  disappeared,  even  in  man,  where  it  is  less  than  in  animals  ;    but. 


C.  of  PurMiige 


Term, 
basket 


C.  ne'ir 


Mossy  fihre 


Fig.    153. — Structure  of  the  cerebellar  cortex. 


Section  of  a  convolution.     Diagram  after  Cajal,  slightly  modified.     The  cell  of  Parkinje  is 
seen  from  the  front. 


according  to  the  preceding  authors,  these  reflexes  are  not  the  normal  equivalents 
of  those  aroused  by  stimulation  of  the  skin  or  of  a  tendon  in  a  healthy  individual, 
or  even  in  one  attacked  by  cerebral  lesions.  They  retain  their  interest  from  the 
point  of  view  of  the  general  i^hysiology  of  the  nervous  centres  ;  they  have  no 
diagnostic  value  with  regard  to  the  seat  of  mesencephalic  or  medullary  cerebral 
alterations. 

Anatomical  data. — The  cortex  of  the  cerebellum  is  formed  of  two  superposed 
layers,  one  of  grey  {molecular  layer),  the  other  of  a  yellowish  aspect  (granulated 
layer).  Between  their  boundaries  are  situated  the  cells  of  Purkinje,  whose 
dendritic  prolongations  extend  in  the  first,  while  their  axis-cylinder  prolongation 


SUPERIOR  SYSTEMATIZATIONS 


383 


passes  througli  the  second.     Tliese  elements  are  still  more  characteristic  of  the 
cerebellar  cortex  than  are  the  pyramidal  cells  of  that  of  the  brain. 

Cells  of  Purkinje. — These  cells  have  more  analogy  than  one  with  those  of  the 
second  layer  of  tlie  brain.  Their  body  is  siu'mounted  by  a  plume  of  dendrites 
which  extends  by  free  ramifications  into  the  molecular  layer,  and  is  continued 
in  the  deep  portion  by  an  axis  cylinder,  which  is  lost  in  the  medullary  substance  ; 
this  axis  cj-linder  throws  out  collaterals  which  re-ascend  into  the  molecular  layer, 
as  though  to  come  into  contact  with  the  dendrites  of  the  neighbouring  cells.  Do 
they  receive  or  do  they  distribute  impulses  in  this  locality  ?  Once  more  we  find 
ourselves  confronted  by  tliis  question  which  experiment  has  left  unanswered. 
It  seems  rather  as  if  the  impulses  running  off  by  the  axis  cylinder,  in  the  direction 
which  is  called  cellulifugal,  must  partly  leave  it  by  these  collaterals,  and  by  them 
be  secondarily  propagated  to  neighbouring  cells,  which  thus  are  associated  in 
function  with  the  cell  receiving  the  initial  impulse.  There  would  in  this  way  be 
not  only  cells  (short  neurons)  of  association,  but,  in  the  true  sense  of  the  word, 
fibres  (jDrolongations)  of  association,  thrown  between  neurons  of  the  same  natvire 


P"        -  I'arallel  F. 


C.  of  Purlinjp 


Giran. 


Fig.    154. — Structure  of  the  cerebellar  cortex. 

Frontal  section  of  a  convolution,  after  Kolliker. — The  cells  of  Pm-kinje  are  seen  in  profile 
and  the  parallel^fibres  from  the  front. 


as  are  these  latter  ;  the  pj-ramidal  cells  of  the  brain,  and  the  cells  of  the  anterior 
horns  of  the  spinal  cord  show,  on  the  other  hand,  a  similar  arrangement. 

The  cells  of  Purkinje  are  obviously  elements  which  conduct  the  impulse  away 
from  the  cerebelhun,  after  having  received  it  therein.  It  is  not  known  to  what 
nervous  organ  they  transmit  it  ;  their  analogy  of  form  with  the  j^yramidal  cells 
of  the  cerebral  cortex  would  tend  to  show  their  connexion  with  the  spinal  cord. 

Climbing  fibres  and  mossy  fibres. — As  comiterpart  to  the  cells  of  Purkinje, 
axis-cylinder  terminations  will  be  found  in  the  cortex  of  the  cerebellum  which, 
in  an  equally  obvious  manner,  carry  to  it  impulses  coming  from  elsewhere  :  these 
are  the  climbing  fibres  which  terminate  in  the  molecular  layer  by  rolling  their 
arborizations  around  the  dendritic  prolongations  of  the  cells  of  Purkinje,  and  the 
mossy  fibres  which  terminate  in  the  granular  layer  around  the  cells  belonging  to 
it  (the  granules). 

On  the  other  hand,  we  know  that  the  cerebelhun  is  united  to  its  adjacent  organs 
below  (spinal  cord,  medulla  oblongata,  pons)  and  above  (cerebral  cortex,  optic 
thalamus)  by  its  three  double  peduncles,  not  to  speak  of  its  o-wm  nuclei  (corpus 
dentatum,  nucleus  of  the  roof)  and  the  connexions  which  either  these  bodies,  or 


384  SYSTEMATIC    FUNCTIONS 

its  cortex,  contract  witli  masses  of  lesser  importance,  such  as  the  red  nucleus 
(above)  and  the  bulbar  olive  (below).  It  is  very  difficult  to  ascertain  exactly 
which  of  the  preceding  elements  (which  we  can  only  call  cerebellifugal  and  cerebel- 
lipetal),  serve  to  effect  such  and  such  of  these  numerovis  connexions. "^ 

Cells  of  association. — The  cells  of  association  are  distributed,  some  in  the  mole- 
cular layer,  and  others  in  the  granular  layer. 

Molecular  layer. — It  contains  stellate  cells  of  small  volume.  The  short  rays  of 
these  cells  seem  to  be  those  which  receive  the  impulses.  On  the  contrary,  two 
of  these  rays,  situated  in  each  other's  prolongations,  form  a  double  axis  cylinder 
extending  for  a  certain  distance  in  two  opposite  directions.  Their  orientation 
is  remarkable  ;  they  are  situated  in  the  plane  which  contains  the  plmnes  of  the 
cells  of  Purkinje,  and  consequently  perpendicularly  to  the  direction  of  the  layers 
and  tangential  to  these  layers.  At  the  level  of  each  cell  of  Piu-kinje  a  collateral 
is  detached,  which  furnishes  around  the  body  of  this  cell  a  veritable  network, 
enclosing  it  with  its  free  ramifications,  like  a  sort  of  basket,  whose  very  narrow 
opening,  closed  on  the  cell,  allows  its  axis  cylinder  to  pass  through. 

The  cells  of  Purkinje  are  thus  mutually  associated,  in  the  direction  of  the 
thickness  of  the  layers. 

Granular  layer. — Subjacent  to  the  i^receding,  this  laj-er  contains  small  poly- 
hedral cells  (the  granules)  which  repeat,  under  new  forms  and  arrangements,  the 
preceding  associating  disposition.  Furnished  with  short  dendritic  prolongations 
by  means  of  which  they  receive  the  impulse,  these  cells  give  out  an  axis  cylinder 
which  at  first  follows  an  ascending  axial  direction  in  order  to  reach  the  molecular 
layer  :  once  there,  it  bifurcates  to  right  and  to  left  and  becomes  tangential  ;  its 
orientation  is  in  the  same  direction  as  the  layers  which  it  follows  from  one  end 
to  the  other,  and  is  conseqviently  perjjendicular  to  all  the  preceding  {parallel 
fibre  of  Cajal). 

It  gives  off  no  collateral,  but  traverses  all  the  plmnes  of  the  cells  of  Piu'kinje 
IDerpendicularly  to  their  plane  and  thus  connects  these  cells  in  the  direction  of 
the  layers,  as  they  are  already  connected  perpendicularly  to  this  direction.  One 
variety  only  of  cells  does  not  conform  to  these  more  or  less  geometrical  types ; 
these  are  the  large  stellate  cells,  whose  ramifications^  both  those  of  the  axis 
cylinder  and  protoplasmic,  proceed  in  all  directions. 

Connexions  of  the  Cerebullum  studied  according  to  the  method  of  degeneration 

A.  Hemisection  of  the  spinal  cord. — a.  Ascending  and  descending  degenera- 
tion in  the  spinal  cord. — (1)  In  the  posterior  columns  (descending  and  of  slight 
extent)  ;  (2)  In  the  direct  cerebellar  tract  (the  whole  extent  in  both  directions)  ; 
(3)  In  the  anterior  columns  (two  directions  and  rather  far)  :  (4)  In  the  lateral 
colmnns  (two  directions,  but  near  the  section). 

b.  Degeneration  in  the  cerebellum. — Degeneration  of  the  i^eriphery  of  the  lateral 
colmnn  going  to  the  cerebellum  ;  direct  course  withovit  decussation  as  regards 
most  of  the  fibres  ;  it  passes  into  the  restiform  body,  into  the  dorsal  convolutions 
of  the  vermis  ;  two  other  tracts  going  to  the  vermis  or  to  the  median  nuclei  of 
the  cerebellmu. 

B.  Lesions  of  the  cerebellum. — Descending  degeneration. — (1)  Short  path 
of  association  (corresponding  side)  ;  short  commissiu-al  path  (opposite  side). 
(2)  Long  crossed  path  ;    a  small  portion  for  the  acoustic  field  of  Alilborn  ;    a 

1  This  example  shows  clearly  how  fundamentally  indefinite  are  the  designations  of 
centrifugal  and  centripetal,  of  motor  and  sensory,  so  often  applied  to  neurons  having  no 
immediate  relation  with  the  peripliery.  The  cerebellmii  is  an  important  centre,  but 
this  centre  is  subordinate  to  the  brain  and  the  fibres  uniting  the  one  to  the  other  in  two 
contrary  directions,  leaving  one  centre  in  order  to  attain  another,  are  all  of  them  simul- 
taneously centrifugal  and  centripetal.  For  fibres  of  association  uniting  equivalent 
regions  of  the  cortex  of  the  brain,  the  unsviitability  of  the  terms  above  designated  is 
still  more  evident. 


SUPERIOR  SYSTEMATIZATIONS 


385 


larger  portion  passes  by  the  posterior  (inferior)  cerebellar  peduncle  into  the 
medulla  oblongata  and  the  lateral  column  of  the  spinal  cord  ;  notliing  in  the 
telecephalon  and  the  mesencephalon. 


In  order  to  elucidate  the  function  of  the  cerebellum  there  are  two 
methods  of  procedure  :  the  one  consists  in  separating  it  from  its  natural 
connexions,  by  cutting  its  peduncles  separately  ;  the  other  in  dealing 
directly   with  it, 

by  shcmg  it  ni   a  - —     /'■''  ^"^,    ..^mmm:^ sup.  vermis 

methodical  man- 
ner, or  else  by 
stimulating  it. 


2.     Experimental 
data  and  those 
yielded  by  ob- 
servation 


Dent,  body 


Ventrie. 


Bnrrlaeh 


btrect  cereh.  Ft. 


Col.  o1  Clarke 


A.  Cerebellar 
PEDUNCLES. —  The 
cerebellum  is  at- 
tached to  the 
spinal  cord,  the 
medulla  oblong- 
ata, and  to  the 
brain,  by  six 
peduncles  (two  for 
each).  They  are 
all  formed  of  fibres 
which  may  be  de- 
scribed some  as 
afferent,  and  others 
as  efferent  with  re- 
gard to  ^he  cerebellum  itself  ;  their  mutual  proportion  varies  ac- 
cording to  the  peduncles. 

1.  Inferior  cerebellar  peduncles. — They  contain  fibres  which  arise  : 
{a)  from  the  column  of  Clarke  (by  the  direct  cerebellar  tract  of  the 
spinal  cord)  ;  (6)  from  the  nuclei  of  Goll  and  of  Burdach  (arciform 
fibres)  ;  (c)  nuclei  of  the  auditory,  trigeminal,  glosso-pharyngeal  and 
vagus  (sensorial  tract  going  to  the  nucleus  of  the  roof)  ;  finally  {d)  from 
the  bulbar  olivary  body,  which  draws  them  itself  from  the  spinal  cord, 
with  the  grey  matter  of  which  it  seems  to  be  united  in  a  twofold 
manner.     All  these  fibres  are  grouped  in  the  inferior  peduncle  of  the 

p.  c  c 


Fig.    155.- 


-Diagram  of  the  inferior  cerebellar  peduncles 
(Charpy). 


386 


SYSTEMATIC    FUNCTIONS 


•  Denl.  body 


cerebellum  which,  in  the  neighbourhood  of  the  medulla  oblongata  and 
the  spinal  cord,  takes  the  name  of  restijorm  body,  and  whose  fibres,  in 
this  locality  partly  curved,  are  called  arciform  fibres.  Amongst  the 
efferent  fibres,  one  portion  turns  aside  to  pass  through  the  middle 
peduncle.  The  efferent  fibres  mixed  with  others  reach  the  nuclei  of 
the  bulb  and  the  anterior  horns  of  the  grey  matter  of  the  spinal  cord, 
by  the  path  of  the  anterior  columns  and  the  direct  cerebellar  tract. 

Experiment. — Rolando  and,  later,  Magendie  have  observed  that 
section  of  the  inferior  cerebellar  jDcduncle  causes  animals  to  assume  a 
singular  position,  consisting  of  a  curving  of  the  body  into  an  arch  on  the 
side  of  the  wound.  According  to  Longet,  in  order  to  produce  this 
result  it  is  necessary  that  the  section  should  abrade  the  intermediary 
tract  of  the  medulla  oblongata  subjacent  to  the  restiform  body. 

After  section  of 
the  inferior  cere- 
bellar peduncles 
F 1  o  u  r  e  n  s  has 
noticed  a  tend- 
ency to  kicking  ; 
this,  however,  is 
contested  by 
Longet. 

2.  Middle  cere- 
bellar peduncles. 
— T  h  e  s  e  unite 
the  nuclei  of  the 
pons  to  the  cor- 
tex of  the  cere- 
bellum  ;  they 
also    contain 

afferent  and  efferent  fibres  and,  in  addition  to  these,  commissural  fibres 
mutually  connecting  the  cerebellar  hemispheres,  and  which  therefore 
pass  through  the  median  line  without  interruption. 

The  nuclei  of  the  pons  (annular  protuberance)  are,  in  part,  the  con- 
tinuation of  the  grey  matter  which  is,  in  the  medulla  oblongata,  the 
origin  of  the  motor  nerves  and  the  termination  of  the  sensory  nerves. 
But,  in  the  same  way  as  in  the  medulla  oblongata,  special  formations 
superadded  to  these  nuclei  are  found  in  the  thickness  of  the  pons  (in 
the  interval  between  the  white  tracts  which  cross  in  it,  following  two 
principal  directions.  One  of  these  duplicates  the  structure  of  the 
bulbar  or  inferior  olive  :  this  is  the  pontine  or  superior  olive.  Rudi- 
mentary in  man.  it  is  highly  developed  in  certain  animals,  such  as  the 


Mid.  ped. 


Fig.   156. — The  middle  cerebellar  peduncles. 

Horizontal  section    of    the   cerebellum. — Semi-diagrammatic   figure 
(Charpy). 


SUPERIOR  SYSTEMATIZATIONS  387 

cetacea,  the  cat,  the  sheep  (M.  Duval).  The  others  are  nuclei  of  the 
pons  properly  so  called,  being  more  or  less  condensed  or  diffused  grey 
masses  contained  in  its  substance. 

All  these  formations  are  connected  :  (1)  with  the  periphery  by 
elements,  partly  centripetal  and  partly  centrifugal,  which  they  asso- 
ciate for  the  performance  of  reflex  acts  ;  (2)  with  the  cerebellum  by 
the  ascending  and  descending  fibres  of  the  middle  cerebellar  peduncle, 
and  with  the  brain  by  the  collaterals  of  the  pyramidal  tract  and  the 
two  cortico-pontine  tracts.  The  nuclei  of  the  pons  become  degenerated 
in  cases  of  atrophy  of  the  cerebellum  (Pierret). 

Experiment. — Section  of  the  middle  cerebellar  peduncles  produces 
pronounced  movements  of  rotation,  observed  by  Pourfour  du  Petit, 
rediscovered  and  described  by  Magendie  and  Flourens.  These  move- 
ments may  also  be  observed  after  section  of  the  pons  Varoli  when 
this  is  effected  outside  the  median  line  ;  and  they  are  the  more  rapid 
in  proportion  as  the  section  affects  more  especially  the  middle  peduncles 
properly  so  called.  Magendie  has  also  noticed  an  extraordinary  change 
in  the  position  of  the  eyes,  the  one  on  the  side  of  the  lesion  being  turned 
downwards  and  forwards,  and  that  of  the  opposite  side  upwards  and 
backwards. 

The  movement  of  rotation  is  in  this  case  a  rolling  inovement  ;  it  is 
sometimes  effected  with  such  rapidity  that  the  animal  may  perform 
more  than  sixty  revolutions  in  a  minute.  The  direction  of  the  move- 
ment varies  according  to  the  position  of  the  section  in  the  peduncle. 
According  to  Magendie,  the  rotation  takes  place  from  the  side  of  the 
section.  According  to  Longet  and  Schiff,  this  is  so  when  the  peduncle 
is  attacked  through  the  occipito-atloid  space  which  has  been  laid  bare, 
and  when  the  middle  peduncle  is  cut  posteriorly.  If  the  peduncle  is 
cut  or  injured  in  front,  the  rotation  is  performed  from  the  side  opposite 
the  section  ;  this  is  the  most  usual  direction  of  the  movement,  and  the 
one  remarked  in  certain  clinical  observations.  According  to  Schiff, 
this  difference  is  due  to  the  fact  of  the  corresponding  hemisphere  of  the 
cerebellum  being  injured  in  the  latter  case  ;  but  Longet,  who  has  under- 
taken a  re-examination  of  the  question,  explains  otherwise  this  difference 
in  results.  The  section  made  posteriorly  attacks  the  uncrossed  fibres, 
while  that  in  front  affects  fibres  after  decussation  ;  according  to  this 
author  the  movement  would  be  made  from  the  stronger  towards  the 
weaker  side. 

3.  Superior  cerebellar  peduncles. — Also  formed  of  efferent  and  afferent 
fibres,  these  peduncles  extend  along  the  front  of  the  cerebellum,  decus- 
sate below  the  corpora  quadrigemina,  and  join  the  crus  cerebri,  being 
placed  in  its  superior  layer.     After  a  more  or  less  complete  interruption 

cc* 


388  SYSTEMATIC    FUNCTIONS 

in  the  red  nucleus,  they  continue  their  course  towards  the  optic  thalamus 
and  the  cerebral  cortex. 

Experiment. — Like  that  of  the  middle  and  inferior,  irritation  of  the 
superior  cerebellar  peduncles  gives  rise  to  manifestations  of  sensibility 
(Longet).  The  movements  or  rotation  are  less  easy  to  define  on  account 
of  the  large  amount  of  destruction  necessitated  by  an  operation  on 
these  parts.  Section  of  a  superior  peduncle  produces  an  arched  curve 
of  the  body  on  the  injured  side  and  circus  movements. 

Section  of  the  cura  cerebri  has  the  same  effect  as  that  of  the  superior 
eerebellar  peduncles,  this  no  doubt  arising  from  the  very  great  diffi- 
culty of  operating  in  an  isolated  manner  on  these  tracts,  which  are  in 


Bei  N. 
^^cerWV^,    \'''  '  ,     --:if7W%i^  Direct  t. 


r 


C\  /  /        \,        ,^is^ i 4-t    ,    ^         Siqi-c- 


"^^^      A  /  \m.      xf^^ "' 


Lent,  body 


Fig.    157. — The  superior  cerebellar  peduncles. 
Origin  and  decussation  (senii-diagrainmatic  figure)  (Charpy). 

such  close  vicinity  as  to  become  confused  together.  According  to 
Longet,  the  circus  movement  is  effected  in  the  direction  opposed  to  the 
side  of  the  section. 

4.  Olives  and  nuclei  of  the  pons  :  their  connexions. — The  bulbar 
olive  is  in  strict  developmental  relationship  with  the  dentate  nucleus 
and  the  opposite  lobe  of  the  cerebellum  ;  atrophy  of  this  lobe  brings 
about  that  of  the  olivary  body.  Attached  to  the  grey  matter  of 
the  spinal  cord,  and  also  to  the  cerebellum,  the  olive  is  further  connected 
with  the  brain  by  a  tract  which  follows  the  crus  cerebri  in  its  tegmental 
portion  (tract  of  the  calotte),  and  is  lost  in  the  ne'ghbourhood  of  the  red 
nucleus  belonging  to  the  superior  cerebellar  peduncle. 

Experiment. — The  experimental  destruction  of  the  bulbar  olive  pro- 
duces disturbances  of  equilibrium  both  in  standing  and  walking  (Bech- 
terew).     Its  lesion  in  man  produces  vertigo,  titubation  and  movement 


SUPERIOR  SYSTEMATIZATIONS  389 

laterally  on  the  corresponding  side  ;  in  fact,  a  true  pseudo-cerebellar 
syndrome  (Leclerq). 

The  bulbar  and  pontine  olives  and  the  nuclei  of  the  pons  are  collec- 
tions of  grey  matter  which  are  very  remarkable  on  account  of  the 
connexions  they  establish.  They  can  exchange  impulses  with  the 
periphery  (centripetal  and  centrifugal)  by  the  aid  of  the  grey  bulbo- 
medullary  axis.  With  the  cerebellum  impulses  can  be  exchanged  by 
the  afferent  and  efferent  fibres  of  its  inferior  and  middle  peduncles, 
having  for  aim  the  estabhshment  of  a  definite  function,  namely,  equili- 
bration. Finally  (this  we  have  already  noted  as  regards  the  bulbar 
olive)  they  are  connected  with  the  brain. 

The  po)itine  olive  receives  impulses  from  the  anterior  nucleus  of  the 
acoustic  nerve,  and  also  from  the  acoustic  striae.  It  reflects  these 
impulses  on  the  nucleus  of  the  sixth  nerve,  with  which  it  is  in  relation, 
and  furnishes  them  to  the  cerebellum,  with  which  it  is  also  connected. 

The  nuclei  of  the  pons  can  exchange  impulses  with  the  cerebellum 
by  afferent  and  efferent  fibres.  These  same  nuclei  receive  fibres 
descending  from  the  cortex,  cortico- pontine  fibres,  distributed  in  two 
tracts  {anterior  cortico- pontine  tract,  coming  from  the  frontal  lobe,  and 
posterior  cortico- pontine  tract,  coming  from  the  temporal  lobe).  The 
nuclei  of  the  pons  have  also  with  the  cortex  a  connexion  of  a  special 
nature  :  the  pyramidal  tract  skirts  along  them  and  gives  off  to 
them  numerous  collaterals.  These  connexions  with  the  cortex  form 
the  path  which  is  called  cOrtico-ponto-cerebellar. 

5.  Movements  of  rotation. — These  may  be  produced  by  unilateral 
lesion  of  a  fairly  large  number  of  portions  of  the  nervous  system. 
Vulpian  gives  the  following  enumeration  of  these  parts  :  the  cerebral 
hemispheres,  the  corpora  striata,  the  optic  thalami,  the  crura  cerebri, 
the  pons  Varolii,  the  corpora  quadrigemina  and  bigemina,  the  cere- 
bellar peduncles  (and  specially  the  middle),  and  the  lateral  parts  of 
the  cerebellum,  the  olivary  bodies,  the  restiform  bodies,  the  external 
portion  of  the  anterior  pyramids  (Magendie),  the  portion  of  the  medulla 
oblongata"  in  which  the  facial  nerve  arises  (Brown-Sequard),  the  optic 
ner\^es.  the  semi-circular  canals  (Flourens),  the  auditory  nerve  (Brown- 
Sequard). 

Generalization. — These  movements  may  be  observed  in  all  verte- 
brata  ;  they  may  be  elicited  in  the  frog  and  in  fish.  In  these  a  uni- 
lateral lesion  of  the  isthmus  of  the  encephalon  causes  a  rotation  of  the 
body  round  its  axis,  which  is  less  rapid  than  in  mammals. 

Classification. — These  movements  differ  from  each  other  according 
to  the  situation  of  the  portion  of  the  nervous  system  which  has  been 
injured.     They  may  be  classed  under  three  headings  :    inovements  of 


390  SYSTEMATIC    FUNCTIONS 

rotation  on  the  axis,  like  those  of  which  we  have  just  spoken  ;  move- 
ments like  the  hand  of  a  clock,  the  axis  of  rotation  perpendicular  to  the 
trunk  passing  through  the  posterior  limbs  ;  rotatory  movements  (circus 
movements),  in  which  the  animal  follows  a  circular  tract. 

Differences  according  to  the  injured  part. — Lesion  of  an  anterior 
portion  of  the  encephalon,  such  as  a  hemisphere,  would  cause  circus 
movements.  In  proportion  as  this  injury  approaches  the  pons,  these 
movements  change  into  the  rotation  resembling  the  hand  of  a  clock? 
whether  it  be  that  the  animal  turns  on  its  own  hindquarters  or  whether 
the  imaginary  clock-hand  prolonged  behind  the  body  has  an  axis 
(also  imaginary)  at  a  certain  distance  from  it.  Should  the  lesion 
attack  the  pons  or  the  part  representing  it,  a  rolling  movement  is 
produced. 

Frequent  discussions  have  taken  place  between  observers  or  experi- 
menters concerning  the  determination  of  the  direction  of  rotation  with 
regard  to  the  right  or  left  side,  according  to  which  it  is  effected. 

Rules  for  defining  the  direction  of  the  movement. — Prevost  observes  tliat  these 
discussions  liave  usually  as  a  starting  point,  not  the  divergent  residts  of  experi- 
ments or  of  observations,  but  the  different  conventional  manner  of  defining  the 
movement  of  the  subject  under  observation,  with  regard  to  itself  and  also  to  the 
observer.  This  author  shows  that  the  co7ijuga(ed  deviation  of  the  eyes  and  the 
change  of  position  of  the  head  accomjDanying  it  may  serve  to  define  the  direction 
of  these  movements.  Deviation  of  the  eyes  and  head  is  often  the  starting  point 
for  movements  of  rotation  by  extension  to  the  other  muscles  of  the  body.  The 
relation  of  this  deviation  with  regard  to  the  lesion  is  easy  to  establish  ;  it  is 
durable  :    the  deviation  takes  place  from  the  side  of  the  lesion. 

If,  for  example,  the  cerebral  injury  is  on  the  left,  the  eyes  and  the  head  are 
deviated  to  the  left  (with  regard  to  the  subject  under  observation).  If  a  move- 
ment of  rotation  be  jDroduced,  it  will  cause  the  body  of  the  subject  to  turn  as  on  a 
pivot  in  the  same  direction,  from  right  to  left  with  regard  to  itself.  But  if  the 
subject  falls  on  the  ground  with  the  face  dowTiward,  and  we  observe  it  by  placing 
ourselves  at  its  feet,  it  will  apj^ear  to  roll  from  left  to  right  (with  regard  lo 
our  own  right  and  left),  while  in  reality  continuing  the  same  movement.  All 
descriptions  of  movements  of  rotation  may  be  verified  by  recalling  these  defini- 
tions. 

Paralytic  and  irritative  lesions.  — Clinical  observations  on  conjugated  deviation 
of  the  eyes  and  head  further  teach  us  that  unsymmetrical  movements  or  attitudes 
are  due  to  paralysis  of  the  injiu-ecl  jjarts,  interruj^ted  in  their  continuity,  and  to 
the  predominance  of  action  of  the  symmetrical  nervous  structures  remaining 
intact.  But  further,  in  the  covu-se  of  cerebral  affections  of  a  paralytic  nature 
occasioning  these  deviations,  irritative  lesions  may  take  part  which,  like  those 
observed  by  Landouzy  and  Grasset,  may  change  their  character  (contractvu-es, 
Jacksonian  epilepsy).  These  attacks  are  of  short  diiration,  thus  showing  that 
the  durable  modifications  of  the  attitude,  or  even  the  motor  unsymmetrical 
tendencies  resulting  from  it,  are  really  of  a  paralytic  nature. 

Apart  from  the  cases  of  simple  deviation,  the  mechanism  of  these  changes  of 
position  and  that  of  the  movements  of  rotation  continues  to  be  unknown  and 
very  obscure.  Neither  unilateral  paralysis  of  conducting  fibres  or  of  centres 
duplicated  in  the  nervous  system  (Laf argue),  nor  that  of  adductors  of  one  side 


SUPERIOR  SYSTEMATIZATIONS  391 

coinciding  with  that  of  abdvictors  of  the  other  (Schiff),  nor  the  suppression  of 
restraining  forces  necessary  to  eqiiiUbrium  (Magendie),  nor,  finally,  inliibition 
at  a  distance,  sufifices  completely  to  explain  this  mechanism. 

B.  Effects  of  destruction  of  the  cerebellum. — Destruction  of 
the  cerebellum  may  be  either  total  or  partial.  It  may  be  directed  to 
the  vermis  alone  or  to  the  whole.  It  may  also  bear  upon  half  of  the 
organ,  the  other  half  being  respected.  And,  finally,  it  may  in  the 
vermis  affect  either  its  anterior  or  posterior  portion.  Flourens  removed 
the  cerebellum  by  successive  slices,  observing  the  disorders  produced 
after  each  ablation. 

Three  orders  of  phenomena. — The  primary  effect  is  that  of  stimula- 
tion. This  once  dissipated,  contrary  effects,  called  those  of  supjyression, 
appear,  which  may  be  traced  to  loss  of  the  cerebellar  function.  But 
in  the  long  run  effects  of  substitution  are  manifested,  which,  developed 
by  exercise  and  a  sort  of  new  education,  more  or  less  disguise  the  pre- 
ceding results  in  spite  of  the  lesion  being  irreparable.     It  is  therefore 


Fig.    158. — Attitude  in    repose,  after    destruction    of  the  left  half  of    the  cerebellum 

(after  Thomas). 

difficult  to  maintain  in  a  purely  isolated  condition  either  one  or  the 
other  of  these  orders  of  phenomena.  And  authors  also  hesitate  con- 
cerning the  duration  of  each  of  these  phases.  Some,  with  Luciani, 
give  great  importance  to  the  effects  of  irritation  ;  others,  with  Thomas, 
restrict  them  to  the  moment  of  operation  (action  of  instruments,  com- 
pression by  clots  of  blood).  The  criterion,  as  regards  their  distinction, 
is  to  seek"*for  the  inversion  of  effects,  which  will  be  more  marked  in 
proportion  to  the  length  of  time  elapsed  since  the  operation. 

We  will  describe  the  effects  of  destruction  of  the  cerebellum,  taking 
as  a  guide  the  very  circumstantial  description  given  of  it  by  Thomas. 

1.  Unilateral  destruction. — Effects  consecutive  to  the  operation. — 
There  is  conjugated  deviation  of  the  eyes  in  the  direction  opposite  to  that 
of  the  lesion,  combined  with  nystagmus.  If  placed  upright,  the  animal 
falls  on  the  side  of  the  lesion,  and  rolls  on  the  longitudinal  axis  of  the 
body,  this  movement  continuing.  These  movements  are  spontane- 
ously reproduced  with  intervals  of  repose  during  the  first  days  after 


392  SYSTEMATIC    FUNCTIONS 

the  operation,  and  also  on  the  least  irritation,  painful,  acoustic  or 
tactile. 

In  repose,  the  animal  is  contracted,  and  lies  on  the  side  operated  on, 
the  head  stretched  out  and  thrown  back  towards  the  side  of  the  lesion  ; 
the  limbs  (especially  the  anterior)  are  extended  and  more  contracted 
on  the  side  operated  on.  The  trunk  is  inflected  (pleurothotonos)  with 
the  concavity  turned  towards  the  lesion.  This  attitude  is  at  first 
irresistible,  and  the  animal  returns  to  it  when  disturbed. 

Amendment  of  the  disorders. — After  four  or  five  days,  amelioration 
of  these  disorders  appears,  and  the  animal  endeavours  to  perform 
several  movements.  It  can  tolerate  decubitus  on  the  stomach,  by 
keeping  its  limbs  very  widely  separated.  Up  to  this  time  the  tendon 
reflexes  are  increased,  but  their  increase  then  gives  place  to  a  diminu- 
tion of  tonicity  ;  the  increased  reflexes  are  considered  to  be  the  effect 
of  irritation. 

Immediately  after  the  operation  the  animal  has  difficulty  in  swalloiv- 
ing,  so  great  that  the  act  is  almost  impossible.  This  symptom  quickly 
disappears,  while  the  prehension  of  food,  necessitating  external  adapted 
movements  of  the  head,  remains  difficult  for  a  long  time  on  account 
of  the  oscillation  of  the  latter. 

After  fifteen  or  twenty  days,  the  animal  can  hold  itself  upright, 
maintaining  its  equilibrium  on  its  Avidely  stretched-out  hmbs.  If  it 
tries  to  raise  a  forepaw  (generally  that  of  the  side  operated  on),  this 
change  of  position  is  no  longer  effected  by  compensatory  move- 
ments bringing  back  the  axis  of  the  centre  of  gravity  within  the  base 
of  support  thus  displaced  and  reduced  :  the  animal  falls  heavily  on 
the  side  of  its  cerebellar  lesion.  These  phenomena  during  standing 
and  walking  are  accompanied  with  trembling  and  oscillations  of  the 
body,  which  speedily  bring  about  fatigue  and  accelerate  the  respiration. 
The  muscles  of  the  injured  side  seem  feebler,  and  their  movements  are 
abruptly  performed. 

Little  by  little  elevation  of  the  anterior  paw  can  be  effected,  then 
that  of  the  hindquarters  ;  walking  and  running  become  possible.  These 
corrections  are  made  by  a  new  mechanism  and  by  efforts  of  substitution 
on  the  part  of  organs  :  but  movement  is  without  suppleness,  and  has 
a  rigid  and  intentional  character,  not  shown  in  the  ordinary  purely 
automatic  movements  of  walking  in  animals. 

Simple  equilibria  independent  of  the  cerebellum. — Sirimming,  on 
the  contrary,  becomes  possible  much  sooner  and  more  easily,  because 
the  conditions  of  equilibrium  are  here  incomparably  simpler  than  in 
walking.  The  position  of  the  trunk  in  the  water  is  not,  however,  sym- 
metrical, the  healthy  side  plunges  more  than  the  side  operated  on  ; 


SUPERIOR  SYSTEMATIZATIONS 


393 


the  head  inehnes  shghtly  toward  the  healthy  side  ;  and  progression 
is  effected  with  sh'ght  deviation  toward  it. 

Co-ordination    and    equilibration    of    medullary    origin. — Tarchanoff 
has  observed  that,  after  decapitation  (section  of  the  spinal  cord  in  the 
middle  of  the  neck),  a  duck  is  able 
to    preserve   its  equilibrium  in  the  o,         ^ 

water,  but  not  on  the  ground.  The 
spinal  cord  of  this  bird  contains 
associations  Avliich  are  sufficient  to 
ensure  regular  movements  for  remain- 
ing upright  in  the  water  and  for 
swimming,  while  standing  on  the 
ground  and  walking  represent  a 
much  more  complicated  equilibrium, 
which  requires  the  assistance  of 
other  associations  (especially  the 
cerebellum).  Section  of  the  neck 
and  spinal  cord  causes  an  excita- 
tion which  brings  this  mechanism 
into  play  for  a  short  space  of  time. 
A  fresh  section  provokes  a  fresh 
bout  of  swimming  (and  even  of 
flight).  An  external  stimulation  has 
the  same  effect  ;  or  it  may  some- 
times arrest  the  movement  just  be- 
ginning to  be  performed. 

2.  Total  destruction. — As  Vulpian 
and  Schiff  have  remarked,  total 
destruction  of  the  cerebellum  is  fol- 
lowed by  effects  which  are  apparently 
much  less  serious  than  partial  de- 
struction^affecting  half  of  the  organ. 
This  may  be  understood  with  re- 
gard to  an  apparatus  whose  function 

is  to  preserve  equilibrium  by  bringing  bilateral  forces  into  play,  many 
of  which  are  reciprocally  antagonistic.  But  if  the  movements  of  rota- 
tion are  suppressed,  the  effect  resulting  from  this  suppression  is  again 
displayed  by  disturbance  in  the  position  ;  the  head  is  forcibly  extended, 
the  trunk  is  in  opisthotonos,  the  limbs  (especially  the  anterior)  con- 
tracted, there  is  nystagmus  ;  then,  when  the  movements  return,  titu- 
bation,  oscillations  and  trembling,  as  much  and  more  than  in  partial 
destruction. 


Fig.  15*J. — Tracing  of  the  gait  of  a 
dog,  after  ablation  of  the  left  half 
of  the  cerebellum,  taken  at  the 
period  of  restoration  of  function. 

Fore  paws  in  white  ;  hind  paws  in  black. 
On  the  right,  tracing  of  norn:al  gait 
(scale  ^V)-  On  the  left  tracing  of  the  gait 
of  dog  operated  on — exaggerated  separa- 
tion of  the  paws  and  irregular  gait.  Below, 
normal  extent  of  the  separation  of  the 
paws  in  a  position  of  repose  (after  Thomas). 


394 


SYSTEMATIC    FUNCTIONS 


3.  Destruction  of  the  vermis. — Its  effects  resemble  those  of  total 
destruction,  but  are  more  rapidly  recovered  from  :  antero-posterior 
movements  of  oscillation,  and  a  tendency  to  kicking. 

4.  Predominating  direct  action. — In  the  brain  it  is  the  crossed  action 
which  predominates  :  in  the  cerebellum,  on  the  contrary,  it  is  the 
direct  action.  Each  cerebellar  hemisphere  exerts  a  bilateral  action,  but 
one  which  is  predominant  on  the  sa^ne  side.  Each  half  of  the  cerebellum 
has  its  principal  connexions  ivith  the  opposite  cerebral  hemisphere  and 
with  the  half  of  the  spinal  cord  of  the  same  side  (Luciani). 

In  certain  cases  it  has  been  observed  that  atrophy  of  a  cerebellar 
hemisphere  corresponds  with  that  of  the  cerebral  hemisphere  of  the 


H-C^illet 


Fig.    100. — Attitude  in  repose,  after  total       Fig.    161. — After  destruction  of  the  vermis, 
ablation  of  the  cerebellum. 
Period  of  restoration  of  the  functions  (after  Medium   abduction   of   the   anterior   limbs. 

Thomas).  Abduction    and    projection    of    the    posterior 

Urabs  (after  Thomas). 


opposite  side.  The  superior  cerebellar  peduncles  are  very  distinctly 
decussated  as  regards  the  larger  portion  of  their  fibres. 

C.  Electric  stimulation  of  the  cerebellum. ^ — Ferrier,  after 
having  exposed  it,  has  stimulated  the  cerebellum  in  animals,  and 
especially  in  the  monkey. 

a.  In  animals. — The  results  are  as  follows  : — 

(1)  Pi/ramid  of  the  median  lobe. — The  eyes  move  liorizontally  in  the  direction  of  the 
point  of  application  of  the  electrodes. 

(2)  Superior  vermiform  process. 

f  In  the  middle  :   The  eyes  look  downward. 
Posterior  extremity.       [  Qn  one  side  :      They  look  down  on  tlie  same  side. 

,    ,     .  ,        .,  i  In  the  middle  :  The  eyes  look  upwards. 

Anterior  extremity.        y^^^  ^^^  ^-^^    .     r^^j^^^  ^^^^  ^^^  ^^^^  ^o  ^1^^  g^^,„g  gj^p_ 

(3)  Lateral  lobe. — The  eyes  look  up  and  from  the  stimulated  lobe. 

(4)  Flocculus. — The  eyes  turn  on  their  antero-posterior  axes. 

The  head  when  left  free  is  the  seat  of  movements  coinciding  with 
those  of  the  eyes  :  elevation,  depression,  etc.  There  is  further  a 
tendency  to  certain  abrupt  and  intermittent  movements  of  the  upper 
limbs,  and  to  extension  of  the  legs  on  the  side  corresponding  to  the 


SUPERIOR  SYSTEMATIZATIONS  395 

stimulation.  In  the  pigeon  the  head  alone  is  displaced  and  not  the 
eyes,  and  movements  of  the  wing  and  the  claw  may  be  noticed.  In 
fish  the  eye  on  the  side  stimulated  protrudes,  the  tail  is  curved  inwards 
on  the  same  side,  and  the  fins  are  spread  out  ;  if  the  stimulus  is  a  median 
one,  both  eyes  protrude  and  the  tail  curves  upward. 

b.  In  7nan. — Purkinje  and,  later,  Hitzig,  have  stimulated  the  cere- 
bellum in  man  by  passing  a  galvanic  current  of  medium  intensity 
through  it,  the  poles  being  respectively  placed  behind  each  ear,  near 
the  mastoid  process. 

The  subjective  result  of  this  stimulation  is  a  sensation  of  vertigo,  char- 
acterized by  an  apparent  displacement  of  objects  in  the  direction  of 
the  current  :  from  right  to  left,  if  the  positive  pole  is  to  the  right,  or 
conversely. 

The  motor  result  is  a  depression  of  the  head  and  the  body  on  the  side 
of  the  positive  pole.  This  displacement  of  the  head  is  also  accom- 
panied, as  Hitzig  has  demonstrated,  with  movements  of  the  eyes  in  the 
same  direction,  and  often  by  nystagmus. 

Remark, — In  animals  in  which  it  is  possible  to  uncover  the  cere- 
bellum, stimulation  is  effected  by  placing  the  two  poles  on  the  region, 
or  on  the  side  of  which  it  is  intended  that  the  activity  should  be  mani- 
fested (bipolar  stimulation).  In  man,  where  the  electricity  must 
penetrate  through  the  bones  of  the  skull,  this  mode  of  stimulation  is 
not  applicable,  because,  on  account  of  the  electrodes  being  too  near 
together,  the  current  would  only  penetrate  the  skin  and  not  reach  the 
deeper  structures.  It  is  forced  to  traverse  (at  least  by  a  portion  of 
its  lines  of  flux)  the  intracranial  organs  to  be  stimulated,  by  placing 
the  two  poles  on  two  symmetrical  regions  at  the  extremity  of  one  of 
the  diameters  of  the  organ  (in  this  case  the  transverse  diameter) .  When 
it  is  remembered  that  the  two  poles  have  a  very  unequal  stimulating 
value,  the  negative  pole  or  cathode  greatly  preponderating  over  the 
positive  pole  or  anode,  the  result  is  the  same  as  if  the  stimulating 
current  were  applied  only  to  the  region  where  the  cathode  is  placed 
(unipolar  excitation). 

1.  Agreement  of  the  results. — Hence  it  follows  that  the  motor  results 
of  stimulation  of  the  cerebellum  in  man  are  in  unison  with  those  ob- 
tained in  animals.  In  both  cases  the  eyes  are  directed  to  the  side 
opposite  to  that  which  is  being  stimulated. 

These  results  also  agree  with  those  obtained  by  symmetrical  destruc- 
tion. In  fact,  this  destruction  ought  to  have  results  contrary  to  those 
following  excitation  :  and  we  have  seen  that  it  is  followed  by  a  dis- 
placement of  the  visual  axis  on  the  same  side  as  the  lesion,  which  is 
conformable  to  the  logic  of  facts. 


396  SYSTEMATIC    FUNCTIONS 

2.  Functional  relations  of  the  cerebellum  and  the  brain. — Luciani 
and  Russell  have  studied  the  influence  of  cerebellar  destructions  (uni- 
lateral) on  the  excitability  of  the  cerebral  hemispheres.  They  agree 
in  maintaining  that  this  excitability  is  augmented  in  the  hemisphere 
of  the  opposite  side  :  it  may  also  be  increased  in  both  hemispheres,  but 
unequally  (Luciani).  Under  the  name  of  cerebral  excitability  is  in- 
cluded the  excitability  of  a  complex  system,  beginning  in  the  brain 
and  terminating  in  the  muscles,  and  of  which  the  two  principal  seg- 
ments, the  brain  and  the  spinal  cord,  has  each  its  own  special  excita- 
bility, and  may  present,  therefore,  its  own  variations  of  this  excitability. 
If  we  remember  that  the  cerebellum  is  at  the  same  time  united  to  both 
of  these  two  segments,  we  shall  realize  how  uncertain  and  obscure  is 
the  mechanism  of  this  hyper-excitability,  without  taking  into  account 
that  it  may  be  due  to  a  phenomenon  of  evolution  belonging  to  the 
functional  compensation  of  cerebellar  paralysis.  In  fact,  as  a  result 
of  ablation  of  a  cerebellar  hemisphere,  an  unusual  development  of  the 
anterior  portion  of  the  brain,  principally  of  the  sigmoid  gyrus,  has  been 
observed  (Bianchi).  However,  Russell  has  noticed  that  this  hyper- 
excitability  exists  almost  immediately  after  the  cerebellar  lesion. 

Antagonistic  action. — The  same  author  has  studied  the  antagonistic 
actions  of  the  cerebellar  and  cerebral  hemispheres  of  the  same  side  and 
the  correlated  actions  of  the  opposite  lobes.  Simultaneous  lesions  of 
the  cerebellar  and  cerebral  areas  of  the  same  side  may  be  combined  in 
such  a  way  as  to  leave  the  position  of  the  eyeballs  intact  ;  and  the 
same  may  be  said  with  regard  to  their  excitation. 

Inhibitory  elements. — The  existence  of  inhibitory  elements  in  the  cerebellum 
resembling  those  found  in  the  brain  has  so  far  not  been  proved.  In  each  case 
the  search  for  these  elements  is  surrounded  with  difficulties,  on  account  of  their 
being  so  closely  blended  with  other  elements  whose  function  is  opposed  to  them. 
At  the  same  time  it  is  probable  that  these  elements  exist  in  the  cerebellum  as 
well  as  in  all  the  other  deeply  situated  structui-es  of  the  nervous  system.  It  is  a 
law  universally  recognized,  that  these  elements  are  present  in  all  the  nerve  tracts 
which  connect  the  different  regions  of  the  grey  matter  with  each  other.  All 
systems,  however  elementary,  appear  to  contain  them  in  conjunction  with  the 
elements  excitatory  of  movement.  The  presence  of  these  inhibitory  elements 
seems  to  be  a  condition  necessary  to  the  balance  of  force  in  all  these  systems,  as 
they  regvilate  the  excitations,  and  place  them  in  equilibrivun  and  also  act  as 
economizers  of  nervous  force.  Complex  systems  like  the  cerebellum  and  the 
brain  may,  in  connexion  with  each  other,  play  by  turns  the  part  of  exciting  or 
inhibitory  agents  according  to  circumstances  ;  but  to  neither  does  each  function 
exclusively  belong. 

3.  Cerebellar  vertigo. — The  sensation  of  vertigo  which  results  from 
the  artificial  (electrical)  stimulation  of  the  cerebellum  is  a  phenomenon 
of  conscious  sensibility  which  can  hardly  be  explained  except  by  the 


SUPERIOR  SYSTE3IATIZATI0XS  397 

fact  that  the  cerebellar  stimulation  spreads  to  the  cerebral  cortex. 
The  uncomfortable  sensation  caused  by  it  very  closely  resembles  the 
pain  aroused  by  all  sensory  phenomena  whose  strength  exceeds  the 
normal  (physiological)  limits.  It  tends  to  prove  that  centripetal 
elements  exist  in  the  cerebellum,  whose  function  it  is  to  indicate  to  us 
the  position  of  our  bodies  in  relation  to  external  objects.  These  centri- 
petal elements  exist  in  it  conjointly  with  motor  elements  which  act  by 
maintaining  the  persistence  of  this  position  within  certain  limits. 

Reflex  cycle  of  equilibration. — Equilibrium  in  the  upright  position  and  in  pro- 
gression is  the  result  of  a  reflex  cycle,  which  connects  these  two  kinds  of  elements  : 
the  fii-st  of  these  elements  carries  information  to  the  cerebellum,  which  that  organ, 
by  means  of  the  second  elements,  utilizes  for  the  direction  of  the  muscular  con- 
tractions. This  cyclic  process,  while  confined  to  the  cerebellum,  is  an  imcon- 
scious  one  ;  that  is  to  say,  though  it  may  be  in  some  obscure  way  conscious  in 
itself,  it  is  situated  outside  the  personal  consciousness  of  the  subject.  When 
this  process  is  extended  so  as  to  include  the  siu'face  of  the  brain,  it  becomes,  or 
may  become,  a  conscious  one,  without  the  phenomenon  ceasing  to  be  normal,  or, 
so  to  say,  harmonic.  The  appearance  of  vertigo  (as  of  all  pain)  is  an  indication 
of  disorder  and  of  functional  loss  of  harmony :  the  sensory  impulses  are  then 
giving  us  untrustworthy  information  with  regard  to  the  relations  which  exist 
betw  een  our  bodies  and  the  external  world.  In  space  the  impulses  penetrate 
the  cycle  in  an  abnormal  manner  at  certain  points  of  its  comse,  instead  of  spring- 
ing up  regularly  from  their  usual  point  of  departm-e,  so  as  to  be  renewed  there, 
while  cii'culating  in  it. 

Reciprocal  dependence  of  the  sensory  and  motor  elements.— As  artificial  stimu- 
lation of  the  cerebellum  gives  rise  at  the  same  time  both  to  sensory  and  motor 
phenomena,  it  is  reasonable  to  inquii-e  whether  one  is  the  exciting  cause  of  the 
other,  and  if  so,  which  acts  on  which,  or  if  both  are  elicited  simultaneously.  This 
last  seems  the  most  reasonable  supposition.  It  is  evident  that  the  current  which 
traverses  the  cerebellum  does  not  distinguish  between  the  sensory  and  motor 
elements  which  are  there  mixed  together  ;  and  the  somewhat  strong  stimulation 
which  the  cm-rent  produces  on  these  elements  is  by  them  transmitted  to  others, 
^^■hich  diffuse  it  to  a  gi-eater  or  less  distance  in  different  directions.  The  sensory 
elements,  thus  excited  on  then-  com-se,  carry  to  the  brain,  and  finally  to  the  con- 
sciousness, erroneous  information  concerning  the  situation  of  the  body,  whether 
it  be  at  the  time  in  repose  or  in  movement.     This  is  what  causes  vertigo. 

Vertigo,  as  is  well  known,  arises  when  a  rather  rapid  and  prolonged  rotatory 
movement  is  impressed  on  the  body  in  a  determinate  direction,  as,  for  instance, 
from  right J;o  left.  Wlien  this  movement  ceases,  objects  appear  to  be  displaced 
before  the  eyes  in  the  opposite  direction.  If,  while  the  body  is  in  motion,  the 
eyes  are  moved  laterally  in  a  contrary  direction,  or  if  at  the  moment  when 
motion  ceases  they  make  this  contrary  movement  as  though  to  follow  the  ap- 
parent direction  of  the  moving  objects,  then  vertigo  is  diminished. 

It  is  thus  seen  that  vertigo  is  neutralized  by  the  performance  of  one  of  the 
corrective  movements  which  tend  to  re-establish  equilibrium  (or  which  gives  the 
sensation  of  its  re-establislnnent).  It  is  the  fmiction  of  the  cerebellmn  to  secm-e 
these  corrective  movements  by  co-ordinating  them  with  those  of  the  primary 
movement. 

Comparison  of  the  functions  of  the  brain  and  the  cerebellum.— Compared  with 
the  functions  of  the  brain  properly  so  called  (cerebral  hemispheres),  those  of  the 
cerebellum  are  specifically  very  different.     This  difference  is  demonstrated  very 


398  SYSTEMATIC    FUNCTIONS 

markedly  by  the  experiments  of  Flourens,  consisting  in  the  removal  either  of 
the  cerebral  hemispheres,  or  of  the  cerebellum  alone. 

(a)  Removal  of  the  cerebellum. — The  animal  deprived  of  the  cerebellum,  but  retain- 
ing the  brain,  preserves  unimpaired  all  its  sensibility  and  all  its  spontaneity.  Once 
the  shock  of  the  operation  over,  it  emits  cries  and  is  continually  in  movement 
(Luciani).  It  unsuccessfully  endeavours  to  get  up  and  walk,  and  gives  signs  of 
great  uneasiness,  thus  showing  that  it  has  retained  its  instincts  and  all  its  intelli- 
gence. It  has  in  a  way,  for  the  moment,  completely  lost  its  function  of  equilibration  ; 
or,  in  other  words,  the  faculty  which  it  possessed  of  orientating  the  position  of 
its  body  with  regard  to  the  direction  of  weight,  either  in  an  upright  position  of 
in  progression. 

(b)  Removal  of  the  brain. — The  animal  deprived  of  the  cerehral  hemispheres,  but  re- 
taining the  cerebellum,  presents  an  entirely  different  aspect.  It  has  lost  all  clear  con- 
sciousness of  what  is  passing  around  it,  and  all  spontaneity.  It  remains  motionless, 
does  not  avoid  danger,  neither  seeks  nor  will  take  food  even  if  placed  in  close 
proximity  to  it,  and  manifests  neither  instinct,  intelligence,  nor  sensibility  as 
generally  understood.  Yet  it  has  clearly  preserved  the  faculty  of  equilibration. 
The  bird,  after  the  removal  of  its  brain,  remains  upright  and  motionless  ;  if 
thrown  into  the  air,  it  extends  its  wings  and  svistains  itself  by  their  movements 
while  falling  to  the  earth.  The  voluntary  impvilsion  is  suppressed,  but  the 
automatic  excitation  which  the  movement  gives  rise  to  is  performed  regularly, 
until,  having  once  more  come  into  contact  with  the  grovind,  the  bird  resumes  its 
motionless  position. 

B.  THE  EMOTIONS  :  OPTIC  THALAMUS  AND  CORPORA  STRIATA 
The  impulses  arising  in  the  different  senses  find,  at  the  base  of  the 
brain,  a  locahty  both  for  association  and  reflexion,  whence  pro- 
ceed the  sensori-motor  phenomena  which  are  called  emotio7ial.  The 
connexion  between  sensation  and  movement  is  here  direct  and  close, 
so  that  the  motor  reaction  follows  immediately  on  the  impression  ; 
this  has  caused  the  emotional  phenomena  to  be  compared  to  reflex 
acts.  In  this  locality  the  sensations  acquire  a  greater  value  and  a 
more  complete  organization  than  in  the  grey  bulbo-medullary  axis  ; 
their  effective  tone  also  is  here  very  marked. 

1.  Nervous  reflex  and  conscious  voluntary  actions, — The  foundation 
of  the  classification  of  nervous  sensori-motor  actions  is  based  on  the 
contrast  that  may  be  drawn  between  reflex  and  conscious  voluntary 
acts.  In  the  first  case  the  phenomenon  of  sensation  is  indistinguish- 
able from  the  motor  phenomenon,  the  answer  to  the  stimulus  is 
immediate  ;  the  act  is  unconscious,  automatic  and  performed  in  a 
mechanical  manner.  In  the  second  case  the  two  orders  of  phenomena 
are  dissociated,  and  the  answer  to  the  excitation  may  be  indefinitely 
deferred.  The  act  is  a  conscious  one,  and  as  movement  is  not  closely 
linked,  either  in  time  or  space,  to  the  immediate  sentient  impression, 
and  as  the  relations  have  contracted  great  complexity,  which  appears 
to  imply  the  fact  of  choice,  the  act  may  be  termed  a  voluntary  one. 

2.  Emotional  acts. — The  immediate  connexion  between  movement 


SUPERIOR  SYSTEMATIZATIONS  399 

and  sensation  exists,  or  may  exist,  in  emotion  as  it  does  in  the  reflex 
act  ;  for  the  motor  reaction  is  often  immediate  and  always  invokm- 
tary.  This  reaction  affects  in  a  typical  manner  a  greater  or  less  number 
of  the  muscles,  both  of  external  and  internal,  or  organic,  hfe  ;  in  this 
case  the  effect  is  a  conscious  one  and  produces  a  deep  impression  upon 
us.  Emotion  is  sometimes  called  a  psycho-reflex  action,  on  account  of 
its  mixed  character  of  involuntary  consciousness. 

Starting  point. — The  source,  the  point  of  departure  of  emotion,  as 
in  fact  of  all  nervous  action,  is  always  external  to  ourselves  ;  it  has 
two  modes  of  origin,  and  the  initial  stimulus  which  produces  it  has 
also  two  ways  of  showing  its  effects.  In  the  first  it  acts,  so  to  speak, 
in  a  direct  manner.  In  this  case  emotion  is  at  once  translated  into 
motor  action,  which  is  assimilated  to  the  mechanism  of  an  ordinary 
reflex  act.  The  second  method  is  an  indirect  one,  derived  from  an 
anterior  excitation  retained  in  the  nervous  system. 

In  other  words,  emotion  may  arise  from  a  sudden  impression  (the 
sight  of  some  object,  the  hearing  of  some  sound  .  .  .)  ;  it  may  also, 
on  the  contrary,  be  produced  by  an  idea,  a  remembrance,  or  the  sudden 
drawing  together  of  two  separate  ideas  which  the  brain's  activity  causes 
to  unite. 

External  and  internal  interpretation. — Emotion  is  expressed  extern- 
ally by  motor  manifestations  which  reveal  it  to  the  eyes  of  those  around. 
It  is  also  echoed  by  the  internal  organs  and  the  more  important  func- 
tions (respiration,  circulation,  excretion,  etc.)  ;  when  emotion  is 
powerful  it  affects  the  whole  being.  This  reverberation  caused  by 
emotional  excitement  on  our  internal  organs  is  so  prompt  and  so 
evident,  that  it  has  been  made  the  pretext  for  locating  the  faculty  of 
emotion  in  the  organ  most  directly  affected,  that  is  to  say,  the  heart. 
This  theory,  though  frequently  refuted,  mistaking,  as  it  obviously  does, 
effect  for  cause,  is  continually  finding  supporters.  Doubtless,  if  all 
the  motor  paths  presiding  over  the  internal  and  external  changes  by 
means  of  which  emotion  is  revealed  were  interrupted,  and  if  the 
secondary  effects  of  these  changes  were  wanting,  the  series  of  pheno- 
mena would  be  disturbed  and  emotion  probably  lessened.  But  as 
long  as  the  principal  associations  from  which  these  motor  effects  take 
their  origin  subsist  in  the  deep  masses  of  the  nervous  system,  emotion 
remains  possible. 

It  is  principally  the  subject  of  the  circulatory  modifications  accompanying 
the  emotions  which  has  caused  the  theory  of  their  extra-cerebral  situation  to  be 
formulated.  The  brain,  like  every  other  organ,  is  dependent  on  the  circulation. 
Deprived  of  blood,  it  ceases  to  perform  its  functions.  Taking  this  easily  verified 
fact  as  a  point  of  departiu-e,  some  have  supposed  that  the  brain  passively  submits 


400  SYSTEMATIC    FUNCTIONS 

to  the  oscillations  of  the  general  pressure,  and  that  its  activity  follows  these 
oscillations,  whose  rebound  it  cannot  avoid.  The  primum  movens  of  emotional 
reaction  would  thus  be,  not  in  the  brain,  but  in  the  circulatory  system,  and  the 
former  would  only  translate  it  into  motor  action  by  its  own  particular  kind  of 
activity.  This  theory  is  unsound  at  every  point.  The  brain,  like  every  other 
organ,  depends  on  the  circulation  ;  but,  in  this  point  also  resembling  every  other 
organ,  it  has  regvilating  cycles  at  its  disposal  which  adjust  the  circulation  to  its 
reciuirements.  Sensory  nerves  proceed  from  the  svu-face  of  its  arteries  to  the 
spinal  cord  and  medulla  oblongata,  where  the  vaso-motor  centres  are  situated. 
From  these  centres,  by  which  it  is  reflected,  the  excitation  retvirns  to  the  arteries 
by  means  of  a  double  system  of  constricting  and  dilating  nerves  contained  in 
the  great  sympathetic.  Resembling  that  of  all  other  organs,  the  activity  of  the 
brain,  by  means  of  this  mechanism  of  reflex  and  unconscious  nature,  controls 
its  own  circulation  instead  of  being  controlled  by  it.  Not  only  does  it  govern 
its  own  circulation,  but  it  also  has  the  power  of  controlling  the  nervous  bulbo- 
meduUary  centres,  and  through  these  the  circulation  of  other  organs.  Further, 
it  regulates,  by  joarallel  influences,  the  special  activity  appertaining  to  these 
organs.  The  impulses  which  at  any  given  time  descend  from  the  brain  to  these 
centres  acquire  an  exceptional  intensity  in  strong  emotions,  and  reveal  them 
by  the  temporary  disorder  of  these  activities.  Such  is  the  succession  of  tliese 
phenomena. 

1.    Affective  tone  :  pleasure  and  pain 

The  emotions  are  in  themselves  very  diverse.  They  may  be  divided 
into  two  classes,  according  to  the  affective  tone  to  which  they  respond. 
The  first  class  answers  to  the  call  of  joy  or  phasure,  the  second  to  the 
note  of  sadiiess  or  imin.  The  first  (pleasurable  emotions)  are  accom- 
panied by  an  increased  bracing  of  the  voluntary  muscles,  an  augmenta- 
tion of  the  respiration,  a  vaso-dilatation  of  the  cutaneous  peripheral 
system  and  a  more  vigorous  heart's  action.  The  second  (emotions 
of  sadness)  are  attended  mth  a  disturbance  of  the  innervation  of  the 
voluntary  and  visceral  muscles,  a  cutaneous  vaso-constriction,  and  a 
diminution  of  the  amplitude  of  the  heart's  action.  In  each  of  these 
two  classes  emotion  manifests  numerous  gradations,  and  is  sometimes 
inconsistent.  In  certain  subjects  this  inconsistency  is  carried  so  far 
that  the  affective  tone  may  be  suddenly  overthrown  by  it,  and  some- 
times in  violent  emotion  the  manifestations  proper  to  each  condition 
may  be  partially  intermingled  (laughter  ending  in  tears). 

Being  provoked  by  different  and  special  exciting  causes,  our  sensa- 
tions are  in  themselves  different  and  specialized,  the  specificity  of  each 
sensation  being  connected  with  that  of  the  exciting  cause  by  which 
the  sensation  is  produced.  And  it  will  be  seen  that  this  arrangement 
is  necessary  in  order  that  we  may  have  information  concerning  all 
that  exists  and  occurs  around  us.  'But  this  being  so,  it  must  be  recog- 
nized that  each  sensation  has  two  kinds  of  existence.  One  is  of  an 
agreeable  nature,  that  is  to  say,  pleasurable  ;  the  other  disagreeable,  that 
is  to  say,  painful.     It  rarely  happens  that  a  sensation  is  one  of  absolute 


SUPERIOR  SYSTEMATIZATIONS  401 

indifference  to  us,  in  spite  of  appearances  to  the  contrary.  Over  and 
above  its  original  specific  nature,  each  sensation  has  an  affective  tone 
in  ourselves,  which  appears  to  have  no  purely  physical  origin. 

1.  The  connexion  of  the  emotions  with  different  kinds  of  sensation. — 
Pleasure  and  pain  affect  not  only  the  distinct  and  highly  differentiated 
sensations  which  are  at  the  foundation  of  our  external  relations  (in  the 
senses  properly  so  called),  but  also  those  obscure,  profound  and  latent 
ones  (coenesthesias),  which  rule  in  a  harmonious  manner  the  internal 
relations  of  our  organs  in  the  consensus  which  determines  their  func- 
tions. They  obviously  affect  those  which  subserve  nutrition.  It  is 
thus  that  hunger,  thirst,  and  that  need  of  oxygen  which  has  no  special 
name  in  ordinary  language,  seeing  that  we  obtain  this  necessity  of  respir- 
ation without  being  forced  to  struggle  for  it,  are  affective  conditions,  to 
be  classed  under  the  heading  of  pain,  just  as  their  opposites,  being 
conditions  of  need  in  a  state  of  satisfaction,  would  be  classified  as 
pleasure.  Fatigue,  vertigo,  chilhness,  disgust,  etc.,  are  states  of  being 
of  the  same  nature. 

2.  Determinative  condition. — Pleasure  and  pain  have  this  charac- 
teristic in  common,  that  they  do  not  develop  themselves  or  attain  their 
greatest  intensity  except  by  repetition  or  sumynation  of  the  excitations  ; 
it  is  in  the  sense  of  pain,  however,  that  this  determinative  condition 
is  chiefly  manifest.  It  is  by  a  summation  of  this  sort  that  the  muscular, 
articular,  tendinous  and  visceral  sensibilities  are  enabled  to  reach  the 
threshold  of  consciousness,  below  which  they  are  normally  located,  and 
to  become  of  a  really  painful  nature. 

Transition  from  pleasure  to  pain. — In  the  senses,  properly  so-called, 
it  is  known  that  the  slightest  changes  in  the  intensity  of  the  exciting 
cause,  or  simply  the  persistency  of  its  action,  may  bring  about  an  easy 
and  often  rapid  transition  from  a  state  of  pleasure  to  one  of  pain.  It 
is  also  known  that  the  fact  of  summation,  which  is  at  the  basis  of  these 
two  conditions,  is  equally  displayed  by  the  'persistence  of  the  agreeable 
sensation,  and  even  more  so  hy  the  contiiiuance  of  the  j:ai7iful  one,  after 
the  removal  of  the  exciting  cause. 

Relationship  with  the  psychical  functions. — The  intensity  of  these  two  condi- 
tions, as  regards  equal  exciting  causes,  varies  greatly  according  to  species,  race, 
and  the  individual.  Richet  declares  that  pain  is  notably  "  an  intellectual  func- 
tion which  becomes  more  perfect  as  the  intelligence  is  more  developed."  It  is 
of  small  extent  in  idiots  and  insane  persons.  Its  intensity  is  in  proportion  to 
the  associations  capable  of  being  realized  in  the  nervous  system,  and,  above  all,  in 
the  cerebral  cortex.  Pain  survives  in  the  memory  in  an  acute,  that  is  to  say 
conscious,  state  for  a  certain  time  after  its  exciting  cause  is  removed.  Anaes- 
thetics, by  destroying  the  systematic  associations  which  preside  over  it,  prevent 
pain    rom  arriving  at  the  tlireshold  of  consciousness,  or  perhaps  hinder  if  from 

P.  D  D 


402  SYSTEMATIC    FUNCTIONS 

dwelling  in  the  memory  ;  either  result  is  interpreted  by  us  as  a  proof  of  its  non- 
existence. 

Pain  is  the  internal  revelation  of  functional  disorder.  It  arises  from 
any  cause  which  tends  to  the  disorganization  of  the  elements,  the 
tissues,  or  the  systems  composing  the  economy.  It  is  for  this  reason 
one  of  the  most  habitual  and  constant  symptoms  of  pathological  states, 
conditions  in  which  the  life  of  the  individual,  or  that  of  his  component 
organs,  is  not  undermined,  but  threatened.  The  more  or  less  violent 
motor  reactions  to  which  pain  gives  birth  are  essentially  defensive  ones 
and  appropriate  in  a  greater  or  less  degree  to  fulfil  their  conservative 
intention. 

3.  Non-specific  nature. — Pain  is  not,  therefore,  connected  with  any 
special  exciting  cause,  hut  appears  as  the  consequence  of  every  excitation 
tvhich,  by  its  intensity  or  its  ahnormal  repetition,  transgresses  the  condi- 
tions requisite  for  the  ^naintenance  of  the  functions  in  good  order.  From 
this  it  follows  that  pain  requires  no  special  apparatus  for  its  production. 
There  is  no  organ  of  special  pain  sense,  and  there  are  no  special  con- 
ductors of  pain  (there  are  no  pain  nerves).  There  is  no  system  which 
properly  belongs  to  it  (no  region  in  the  cerebral  cortex  which  is  allotted 
to  it).  Further,  there  is  no  localization,  using  the  word  in  its  ordinary 
sense,  for  the  sensitive  and  sensorial  functions  properly  so  called.  It 
is  true  that  all  pain  is  not  alike  :  it  may  be  described  as  cutting,  burn- 
ing, pricking,  tearing,  acute,  dull,  etc.  :  all  these  terms  recall  more  or 
less  the  mode  of  action  of  the  abnormal  excitants,  capable  of  producing 
it  experimentally,  and  which  are  connected  with  the  variations  of  the 
traumatism  which  produces  the  excitation. 

4.  Habitual  field  of  action. — As  the  surface  of  reception  afforded  by 
the  area  of  touch  is  incomparably  larger  than  that  of  the  other  special 
senses,  and  as  this  surface  comprises  that  of  the  mucous  membranes, 
and  also,  by  gradation,  that  of  the  parenchyma  of  all  the  somatic  or 
visceral  organs,  pain  has  incomparably  more  frequent  opportunities  of 
arising  in  the  field  of  tactile  sensation  than  in  that  of  the  other  senses. 
Practically  it  is  here  alone  that  pain  offers  itself  to  observation  with 
the  characteristics  which  we  are  accustomed  to  recognize  in  it. 

5.  Stimulation  of  nerve  trunks. — Pain  may  have  its  origin  in  intense 
and  more  or  less  destructive  irritations,  not  only  of  the  receptive 
apparatus  of  the  senses,  but  also  of  those  of  the  nerve  trunks,  which 
directly  take  their  origin  in  these  apparatus  (compression,  section, 
puncture,  electrization,  burning,  and  different  mechanical  and  chemical 
actions.  .   .). 

The  action  of  electricity,  so  often  employed  as  an  excitant  in  physiological 


SUPERIOR  SYSTEMATIZATIONS  403 

practice,  is  the  one  most  compatible  with  the  preservation  of  the  organization  of 
all  tissues  and  functions  which  it  presides  over.  Nevertheless,  it  produces  some 
slight  alterations  (electrolytic,  for  example),  but  these  are  quickly  reparable  on 
the  cessation  of  the  passage  of  the  currents.  It  is  this  fact  which  causes 
electricity  to  occupy  a  place  bj-  itself  amongst  analytical  reagents  used  by  the 
physiologist.  All  excitants  of  whatever  nature,  including  the  electric  cvxrrent, 
when  applied  to  a  sensitive  j)art,  usually  show  the  reality  of  their  effect  bj'  pain. 
We  may,  therefore,  reasonably  consider  pain  to  be  an  increased  manifestation 
of  tactile  or  general  susceptibility.  The  functions  of  the  sensory  nerves,  and 
especially  of  their  posterior  roots,  have  been  studied  according  to  the  effects 
wliicli  result  from  their  stimulation ;  these  effects  being  not  simply  tactile,  but 
also  certainly  painful. 

Irritation  of  the  great  sympathetic  may,  by  repetition  and  the  summation 
which  is  the  consequence  of  it,  give  rise  to  pain  of  a  specially  dull  nature. 

6.  Stimulation  of  the  central  masses. — Painful  sensations  may  be 
caused  not  only  by  irritations  brought  to  bear  on  the  sensitive  neurons 
of  the  periphery,  but  also  by  those  which  reach  the  ascending  neurons 
of  the  deeper  systems.  In  this  class  may  be  placed  the  experimental 
excitations  which  may  be  localized  on  the  endogenous  tracts  of  the 
spinal  cord  and  medulla  oblongata.  Certain  clinical  observations  tend 
to  the  same  conclusion  :  foci  of  haemorrhage  or  of  softening  may  some- 
times cause  great  suffering  when  situated  in  the  optic  thalamus,  the 
fillet  {ruhan  de  Heil),  or  the  internal  capsule  (Edinger).  Nevertheless, 
lesions  of  the  encephalic  masses  do  not  present  the  phenomenon  of 
pain  to  a  degree  equal  to  that  shown  by  lesions  of  the  spinal  cord.  It 
is  a  remarkable  fact  that  in  this  point  lesions  of  the  cortex  yield  prece- 
dence both  to  the  spinal  cord  and  to  the  optic  thalamus,  and  enpecially 
to  lesions  of  the  nerve  trunks. 

7.  Stimulation  of  the  cerebral  cortex. — Cephalalgia,  so  frequently 
observed,  is  a  pain  which  it  is  impossible  to  clearly  localize.  The 
brain  is  surrounded  with  membranes,  of  which  one  especially,  the  clura- 
mater,  has  been  found  sensitive  to  experimentation.  Further,  in  this 
membrane  the  existence  has  been  proved,  not  only  of  nerve  fibres,  but 
also  of  sensory  receptive  apparatus  resembling  those  of  the  sensitive 
membranes.  Experimentalists  accustomed  to  practise  stimulation  of 
the  cerebral  cortex  have  not  noticed,  as  an  effect  of  these  stimulations, 
the  sharp  pain  which  follows  that  of  the  posterior  roots,  while  they 
have  observed  that  these  stimulations,  when  directed  to  certain  deter- 
minate points,  give  rise  to  definite  movements.  Therefore  we  infer 
from  this  that  the  organ  ichich  is  usually  considered  to  be  the  seat  of  sensa- 
tion, viz.  the  cerebral  cortex,  shows  no  sensihility  when  the  stimidation 
bears  directly  on  itself.  This  result,  which  seems  startling  at  first  sight, 
will  cease  to  cause  surprise  if  we  take  into  consideration  the  fact  that 
the  stimulus  thus  supplied  to  the  cortex  is  totally  different  from  that 

D  D* 


404  SYSTEMATIC    FUNCTIONS 

which  reaches  it  normally  from  the  sensory  nerves  through  the  medium 
of  the  spinal  cord  and  its  superior  prolongations. 

Development  in  the  field  of  sensation. — It  is  not  merely  the  cerebral  cortex, 
the  optic  thalamus  and  the  spinal  cord  which  cause  sensation  to  become  a  reality, 
making  it,  above  all,  actual,  intense  and  painful ;  it  is  rather  the  whole  formed 
by  these  parts  which  transmits  the  impulse  in  a  determinate  order,  conferring 
on  it  at  each  fresh  halting-place  a  character  which  it  did  not  possess  before  arriv- 
ing there,  this  character,  however,  having  been  elaborated  at  the  previous 
stopping  place.  The  further  we  recede  from  the  cortex  and  the  brain  to  obtain 
a  starting  point  for  the  initial  shock  we  are  about  to  provoke,  in  other  words,  the 
fvu-ther  we  encroach  on  the  nervous  system  to  launch  the  impulse  which  is  in- 
tended to  reach  the  cortex,  so  much  the  more  complete  will  be  the  sensory  effects 
of  this  impulse,  as  experiment  shows  us  and  as  is  also  easy  to  understand.  The 
comparison  of  the  avalanche,  inaccurate  as  applied  to  the  elementary  conductors 
(nerve  fibre),  becomes  an  accurate  one  when  we  apply  it  to  the  field  of  sensation, 
with  its  associations  of  superposed  elements,  its  nmnerous  channels  of  dispersion, 
and  its  complications  of  all  kinds.  In  the  field  of  movement  the  phenomenon 
is  exactly  the  contrary  ;  here  we  find  reduction  and  concentration  of  the  excita- 
tion on  one  extremely  simple  organ,  viz.  the  muscle. 

2.    Expression  of  the  emotions 

1.  Language  of  the  emotions. — In  man  the  expression  of  ideas  is 
conveyed  by  conventional  signs  and  acquired  voluntary  movements. 
There  is,  on  the  other  hand,  an  expression  of  the  emotions  by  involun- 
tary movements,  constituting  a  kind  of  unlearnt  universal  language  ; 
this  language  exists  from  birth,  and  is  found  even  in  those  animals 
whose  organization  approaches  our  own,  principally  the  domestic 
animals.  The  language  of  the  emotions  responds  to  a  double  utility 
and  even  to  a  double  necessity.  It  establishes  a  preliminary  social 
link  between  animals  of  the  same  species,  which  enables  them  to  recog- 
nize the  internal  condition  of  others,  at  the  same  time  imparting 
knowledge  concerning  their  own. 

Moreover,  the  movements,  both  external  and  internal,  aroused  by 
emotion,  although  they  may  not  possess  the  signification  of  a  natural 
language,  play,  for  the  individual  himself,  a  part  both  of  defence  and 
preservation.  A  violent  emotion  arranges  beforehand  the  muscles  and 
the  limbs  in  a  position  suitable  either  for  attack  or  defence. 

Active  and  passive  emotions. — Whether  the  establishment  of  a  relationship 
between  similar  beings  is  in  question,  or  merely  the  preservation  of  the  individvial, 
the  apparently  irrational  movements  which  emotion  gives  rise  to  are  in  reality 
adapted  to  the  necessities  of  each  particular  case.  For  instance,  in  the  emotions 
which  have  a  bearing  on  the  strviggle  for  existence  the  animal,  in  order  to  escape 
from  the  danger  by  which  it  is  menaced,  will  strive  to  arouse  a  feeling  in  its 
adversary  which  would  cause  the  latter  to  keep  aloof  ;  or  it  will  strive  as 
much  as  possible  to  conceal  itself  from  the  sight  of  its  eneniy.  The  elevation  of 
the  voice,  the  horripilation,  the  elevation  of  the  corners  of  the  mouth  to  display 
the  teeth  and  their    grinding,  all  these  are  means  which  come  under  the  first 


SUPERIOR  SYSTEMATIZATIONS  405 

heading  and  show  active  emotion.  Tlie  holding  of  the  breath,  and  the  mimicry 
which  gives  to  animals  the  colour  of  the  soil  or  of  the  vegetation  amongst  which 
thej^  live,  are  means  which  come  under  the  second  heading,  and  may  be  con- 
sidered as  associated  with  passive  emotions.  In  the  conditions  by  which  the 
perpetuation  of  the  species  is  assured,  means  of  the  same  kind  are  to  be  found  ; 
with  this  difference,  however,  that,  in  addition  to  attitudes  and  expressions 
suitable  for  the  driving  away  of  the  enemy,  there  are  others  appropriate  to  the 
drawing  together  of  the  sexes  :  suggestive  sounds  of  the  voice,  the  songs  of  birds, 
and  the  brilliancj-  of  plumage  are  all  means  of  this  description.  In  the  more  or 
less  elementary  social  life  observable  amongst  certain  kinds  of  animals,  the 
expression  of  emotion,  communicated  between  individuals,  has  a  common  pre- 
servation for  its  aim.  Thus,  the  cry  of  fright  given  by  one  acts  as  warning  of 
the  presence  of  danger  to  the  rest. 

2.  Innateness  of  the  emotional  mechanisms. — The  nervous  associa- 
tion.s  which  the  mechanisms  adapted  to  the  expression  of  each  par- 
ticular emotion  display,  are  innate  in  animals.  They  are  transmitted 
by  heredity,  and  differ  therefore  greatly  from  those  accj[uired  by  educa- 
tion, these  latter  being  the  basis  of  language  properly  so  called.  Darwin, 
in  seeking  the  laws  of  these  associations,  refers  them  to  the  three  follow- 
ing principles.  These  principles,  though  throwing  but  a  feeble  light 
on  the  question,  form  the  first  sketch  of  a  rational  explanation  of  the 
emotional  movements  which  has  yet  been  attempted. 

(1)  Principle  of  the  association  of  useful  habits. — Movements  which  in  man 
(and  sometimes  in  domestic  animals)  now  appear  to  be  of  not  the  slightest  utility 
are  continued  in  both  by  heredity,  on  accoxint  of  an  anterior  utility  which  has 
disappeared  owing  to  the  present  conditions  of  existence.  Thus  the  blinking 
of  the  ej-es  and  the  agitation  of  an  aching  limb  have  been  originally,  and  are  still 
occasionally,  movements  useful  for  the  avoidance  of  an  annoying  or  painful  exci- 
tation. These  movements  express,  by  symbolism  and  by  habit,  emotions  analogous 
to  tho.se  by  wliich  they  were  originally  instigated.  Further,  the  conventions  of 
•civilized  life  obhge  us  to  restrain  the  manifestations  of  our  emotions,  but  this 
restraint  is  incomplete  and  allows  the  involuntary  revelation  of  our  internal 
sentiments  to  trans-pire  more  or  less  distinctly,  and  thus  the  faintest  indications 
of  this  nature  become  very  expressive. 

(2)  Principle  of  antiitiesis. — If  any  given  movement  symbolizes  a  certain 
emotion,  it  is  natural  tliat  the  contrary  movement  should  be  chosen  to  signify 
the  opposite  emotion.  A  dog,  imagining  that  he  sees  a  stranger,  immediately 
assumes  a  hostile  attitude,  shown  by  the  stiffening  of  his  limbs  and  the  erection 
of  his  body  and  head.  If  in  this  stranger  he  suddenly  recognizes  his  master,  the 
expression  of  what  he  then  feels  is  shown  in  a  precisely  opposite  manner  ;  in  this 
case  by  a  crouching  attitude,  and  expressive  movements  of  the  limbs,  more 
especially  of  the  tail. 

(3)  Principle  of  direct  action  of  the  nervous  system. — It  would  be  more  correct 
to  call  this  the  overflouing  excitation  ;  this  arises  from  the  fact,  often  observed 
in  phj'siology,  that,  when  sensory  excitation  becomes  too  violent,  it  dift\ises 
itself  all  over  the  nervous  system,  and  also  to  all  the  centrifugal  paths,  whether 
motor  or  inhibitorJ^  Agitation,  cries,  pali:)itation  of  the  heart,  and  generalized 
convulsions,  are  the  effect  of  the  penetration  of  the  excitation  into  the  first  ; 
"while  trembling,  stupor,  emotional  flushing,  and  cardiac  syncope  are  caused  by 
its  extension  into  the  second.     This  principle  is  in  some  small  degree  opposed 


406  SYSTEMATIC    FUNCTIONS 

to  the  preceding  facts,  which  are  rational,  while  it  is  an  empirical  one.  At  the 
same  time  it  is  observable  that  the  attention  demanded  by  the  execution  of 
irrational,  useless  and  aimless  actions  distracts  that  which  is  involuntarily  brought 
to  bear  on  the  pain,  and  thus  acts  as  a  soothing  agent  with  regard  to  the  latter 
[duobus  dolorihus  sitnul  obortis,  non  in  eodeni  loco,  vehenientior  obscurat  alterum). 

In  spite  of  all  the  research  of  which  it  has  been  the  subject,  the 
mechanism  of  internal  motor  reactions  of  an  emotional  nature  is  still 
very  obscure.  As  a  set-off  we  have  very  exact  information  with  regard 
to  the  muscular  actions  which  imprint  such  a  characteristic  emotional 
significance  on  the  features.  This  information  we  owe  to  Duchenne 
(of  Boulogne).  This  author  has  discovered,  in  local  electrization  of 
the  facial  muscles,  a  very  faithful  analytical  method  of  reproducing 
the  expression  of  the  principal  emotions  on  the  face  of  a  subject  who 
is  not  at"  the  time  under  their  influence. 

3.  Emotional  expressions  of  the  human  face. — Emotion  is  shown  on 
the  face  by  the  contraction  of  one  or  more  muscles  which,  arising  from 
a  fixed  insertion  on  the  skull,  displace  certain  portions  of  the  skin, 
either  hollowing  it  into  wrinkles,  or  removing  those  already  existing, 
thus  changing  the  expression.  Amongst  these  muscles  are  some  which 
are  by  themselves  completely  expressive  (frontalis,  corrugator  super- 
cilia,  zygomaticus  major).  Others  are  only  expressive  in  a  coin^iHe- 
mentary  manner,  that  is,  are  only  adapted  to  complete  or  modify  the 
expression  produced  by  other  muscles  (palpebral  portion  of  the  orbi- 
cularis, transversalis  nasi,  platysma  myoides).  Lastly,  there  are  yet 
others  which  are  little  or  not  at  all  expressive,  either  by  themselves  or 
in  association  with  other  muscles  (buccinator).  In  the  association  of 
the  facial  muscles  amongst  themselves,  the  combinations  are  made  up 
of  but  few  elements  (two,  three,  rarely  four  muscles).  These  contrac- 
tions of  the  facial  muscles,  by  themselves  alone  very  expressive,  may 
also  be  combined  with  gestures,  bodily  attitudes,  and  visible  vascular 
and  secretory  modifications  (paleness  or  flushing  of  the  face,  secretion 
of  tears),  all  of  which  complete  the  expression. 

Muscles  of  expression. — Physiological  analysis  has  hardly  investigated 
any  except  the  facial  7nuscles,  which,  after  all,  are  the  most  essential 
element.  The  analysis  consists  in  submitting  these  muscles,  either 
singly  or  in  twos  and  threes,  to  an  artifical  stimulus  (electrical)  directly 
applied  to  them.  The  muscle  or  muscular  association  thus  brought 
into  play  shows  the  external  expression  (purely  objective)  of  an  emotion, 
of  which  the  internal  phenomena  (subjective)  are  entirely  wanting  in 
the  person  experimented  on.  In  order  to  avoid  having  to  take  into 
account  reflex  effects  or  painful  manifestations  which  arise  from  the 
concomitant  stimulation  of  the  sensitive  cutaneous  nerves,  Duchenne 


SUPERIOR  SYSTEMATIZATIONS 


407 


operated  on  an  individual  suffering  from  a  sensory  facial  paralysis,  in 
such  a  way  that  the  stimulus  applied  to  the  neuro-motor  apparatus 
of  the  face  acted  only  on  this  apparatus,  to  the  exclusion  of  any  other. 

Attention  to  external  o6/ec<s.— This  is  characterized  by  an  elevation  of  the  ej-e- 
brow  and  the  upper  eyelid,  wliile  at  the  same  time  transverse  folds  are  formed 
on  the  brow.  This  expression  is  caused  by  the  frontalis  muscle,  whose  insertion 
posteriorly  permits  an  elevation  of  tlie  eyebrow  at  the  moment  of  its  contraction. 
If  exaggerated,  this  expression  becomes  one  of  astonishment. 

Reflection.— nefiection  is  a  state  of  the  mind  which  causes  the  attention  to  be 
concentrated  internally,  to  the  exclusion  of  all  external  impressions  ;  conse- 
quently it  is  a  condition  the  reverse  of  the  preceding  one.  Its  mechanism  is  also 
the  converse  of  that  of  the  latter,  and  is  executed  by  a  muscle  antagonistic  to  the 
frontalis  muscle.  Reflection  is  shown  by  a  lowering  of  the  eyebrow  and  an 
obliteration  of  its  cm-ve,  while  at  the  same  time  the  lines  on  the  forehead  dis- 
appear. 

This  expression  is  caused  by  the  contraction  of  the  superior  half  of  the  orbi- 
cularis palpebrarum  muscle.    , 

Pam.— Both  moral  and  physical  pain  is  shown  by  a  fold  of  the  eyebrow,  which 
is  raised  upwards  and  outwards  by  the  contraction  of  the  corrugator  supercilii. 
This  is  an  oblique  muscle  taking  origin  above  on  the  frontal  bone  inserted  below 


/\ 


Fig.   16-2.— Attention. 
Contraction  of  the  frontalis  muscles 


Fig.    163. — Reflection  ;  meditation. 
Contraction  of  the  orbicularis  palpebrarum. 


in  the  middle  of  the  eyebrow.  Folds  concentric  to  the  inner  cvu've  of  the  eye- 
brow  appear  on  the  brow  close  to  the  root  of  the  nose. 

Menace. — This  is  sho■v^^l  by  a  lowering  of  the  inner  half  of  the  eyebrow,  and  by 
transverse  folds  on  the  root  of  the  nose,  caused  by  the  contraction  of  the  pyra- 
midalis  muscle.  This  muscle  is  inserted  below  on  the  nasal  bones,  above  on  the 
deep  svu'face  of  the  skin  of  the  inter-sviperciliary  space. 

Laughter. — In  laughter  the  commissure  of  the  lips  is  drawn  upwards  and  out- 
wards ;  the  buccal  opening  is  thus  transversely  enlarged,  and  ceases  to  be  recti- 
linear. This  displacement  is  due  to  the  contraction  of  the  zygomaticus  major 
muscle.  A  very  characteristic  fold  of  the  face,  the  naso-labial  furrow,  which 
ends  in  the  commissure,  becoming  displaced  by  being  drawn  upward  and  out- 
ward, and  at  the  same  time  ceasing  to  be  rectilinear,  forms  a  curve  concentric 
M'ith  the  commissure.  The  skin  of  the  cheek  becomes  more  prominent  and  forms 
radiating  folds  toward  the  external  angle  of  the  eye  (crow's  feet),  and  this  aug- 
ments tlie  shadow  below  this  angle,  and  almost  gives  rise  to  the  belief  that  the 
eyelid  has  changed  its  place. 


408 


SYSTEMATIC    FUNCTIONS 


Weejiing. — The  expi-ession  of  weeping  is  the  exact  opposite  of  that  of  laugliter, 
so  far  as  regards  tlie  direction  impressed  on  the  commissure  and  on  tlie  naso- 
labial furrow.  The  commissui'e  is  drawn  downward  ;  the  furrow  is  displaced 
in  the  same  direction,  and  the  crow's  feet  have  a  tendency  to  be  obliterated. 
These  concomitant  displacements  are  due  to  the  contraction  of  the  levator  lahii 
superior  is  and  zygomatieus  minor  muscles.     These  muscles,  more  or  less  parallel  to 


Fig.   164. — Laughter. 
Contraction     of     the     zygomatieus     major 
muscle. 


Fic    U).j. — Weeping. 
Contraction  of  the  levator  labii  superioris. 


the  zygomatieus  major,  have,  like  it,  a  fixed  insertion  on  tlie  cheekbone  or  neigh- 
bom-ing  bones  (internal  edge  of  tlie  orbit)  and,  descending  more  or  less  obliquely, 
liave  tlieir  mobile  insertion  in  the  upper  lip.  But  while  the  zygomatieus  major, 
liaving  the  most  external  position,  is  attached  near  the  commissure,  the  others 
are  inserted  in  the  middle  part  of  the  lip.  From  this  arises  the  obliquity  in  an 
opposite  direction  whicli  is  communicated  to  its  upper  border  by  tlie  contrac- 
tion of  one  or  other  of  these  muscles.     A  third  muscle,  the  levator  labii  superioris 


Fig.    1G6.— Grief. 

Contraction    of    the    corrugator    supercilii 
muscle. 


Fig.    167. — Discontent  ;  scorn. 
Contraction  of  the  depressor  anguli  oris. 


alceque  nasi,  is  attached  above  to  the  internal  border  of  the  orbit  and  below  to 
the  wing  of  the  nose  and  to  the  upjoer  lip,  near  its  median  portion.  Tliis  mviscle 
increases  the  obliquity  of  the  lip,  at  the  same  time  dilating  the  wing  of  the  nose. 
It  raises  en  masse  the  internal  j^art  of  the  naso-Iabial  furrow,  hollowing  it  into  a 
deep  channel  which  is  filled  up  by  tears  ;   this  is  the  muscle  of  violent  weeping. 

Lubricity. — According  to  Duchenne,  the  expression  of  this  feeling  consists  in 
the  vertical  folds  of  the  lateral  surface  of  the  nose,  which  result  from  the  con- 
traction of  the  compressor  narium.     This  is  a  digastric  muscle,  disposed  in  the 


SUPERIOR  SYSTEMATIZATIONS  409 

form  of  a  girth  over  the  bridge  qf  the  nose,  and  attached  by  its  free  extremities 
to  tlie  skin  of  the  cheek  and  nose. 

Disdain,  scorn  and  disgust  derive  tlieu*  expression  from  modifications  of  the 
position  of  the  hps,  especially  of  the  lower  lip.  The  expressions  which  result 
from  the  action  of  pressing  the  lips  together  when  displeased  or  of  pouting,  are 
familiar  to  all  of  us.  These  exjDressions  are  due  to  the  contraction  of  the  orbi- 
cularis oris  of  the  mouth.  In  the  first  case  this  contraction  is  limited  to  the  in- 
ternal fibres  of  the  muscle,  which  press  the  buccal  opening  closely  together  in 
the  same  way  as  a  purse  is  closed.  In  the  second  case  tlie  contraction  is  limited 
to  the  more  eccentric  fibres,  whose  isolated  contraction  causes  the  lips  to  project 
m  the  form  of  a  funnel. 

Tlie  buccinator  muscle,  important  for  mastication,  articulation  and  for  playing 
on  wind  instrimients,  takes  no  part  in  the  expression  of  the  emotions. 

The  depressor  anguli  oris  tnuscle  attached  below  to  the  lower  jaw  outside  the 
symphysis,  has  its  free  insertion  near  the  commissure  of  the  lips.  It  consequently 
lowers  this  commissure,  giving  an  obliquity  to  the  buccal  opening  in  the  same 
direction  as  that  caused  by  weeping ;  but  in  this  ease  the  obliquity  is  cavised  by 
the  lowering  of  the  cominissure  instead  of  the  raising  of  the  middle  part  of  the 
ujiper  lip.  The  naso-labial  furrow  is  drawn  down  and  becomes  almost  rectilinear. 
Slightly  accentuated,  this  expression  is  that  of  sadness  ;  more  accentuated,  it 
becomes  that  of  scorn.  The  semi-occlusion  of  the  eyelids  caused  by  the  contrac- 
tion of  the  orbicularis  palpebrarum  (a  special  mviscle  of  the  ej'elid)  often  accom- 
panies and  completes  this  last  expression  of  the  furrow. 

The  depressor  labii  inferioris  has,  like  the  preceding  one,  its  lower  insertion 
at  the  front  part  of  the  horizontal  branch  of  the  lower  jaw  ;  its  fibres,  which  are 
oblique  both  above  and  inside,  are  inserted  all  along  the  lower  lip.  Contraction 
of  this  muscle,  by  projecting  the  lower  lip,  expresses  disgust. 

The  platysma  myoides,  to  a  bundle  of  which  the  name  of  the  risorious  of  San- 
torini  has  been  given,  is  not  by  itself  a  muscle  of  expression  ;  further,  this  muscle 
expresses  neither  mirth  nor  gaiety,  but  rather  a  grin,  or  a  forced  and  menacing 
laughter. 

3.     Anatomical  data 

Definite  relations  exist  between  the  cerebral  cortex  and  the  sub- 
jacent grey  matter  (which  extends  from  the  thalamus,  the  corpora- 
quadrigemina  and  the  geniculate  bodies  as  far  as  the  grey  axis  of  the 
spinal  cord).  These  relations  are  effected  by  fibres  which,  from  these 
masses  of  grey  matter,  extend  to  the  cortex  ;  conducting  fibres, 
partly  ascending  and  partly  descending.  The  most  accurate  method 
of  ascertaining  these  connexions  is  that  of  the  degenerations  of  which 
the  nerve  fibres  are  the  seat  after  the  destruction  of  the  cerebral  cortex. 
This  degeneration  may  be  produced  experimentally  upon  animals  or 
may  be  occasionally  met  with  in  man  as  a  consequence  of  diseases  of 
the  brain. 

The  degenerations  which,  arising  from  the  destruction  of  the  grey  cortical 
matter,  extend  to  its  subjacent  parts,  are  extremely  niimerous,  as  indeed  are 
all  those  observed  in  these  complicated  regions  of  the  nervous  system.  Amongst 
them  may  be  found  the  three  well  known  varieties  (Wallerien,  ascending  and 
atrophic  degeneration),  distingviishable  from  each  otlier  by  certain  characters. 


410 


SYSTEMATIC    FUNCTIONS 


.-Opt.  thai. 


but  especially  by  the  order  in  which  they  appear.  The  Wallerien  is  the  first  to 
make  its  appearance,  and  is  also  the  most  marked  ;  it  attacks  the  fibres  whose 
cells  of  origin  have  been  either  destroyed  or  separated  from  them  (the  pyramidal 
and  analogous  tracts). 

Ascending  degeneration,  slower  in  its  appearance  than  the  former.  ^)rogi"esses 
upward,  little  by  little,  to  the  cells  whose  terminal  fibres  have  been  cut  or  resected 
{for  example,  the  fillet  [or  ruban  de  Reil]  and  the  nuclei  placed  on  its  course). 
Although  these  two  orders  of  degeneration  are  not  in  all  cases  aljsolutely  easy 
to  distinguish  from  each  other,  it  is  generally  possible  to  make  a  division  between 
the  ascending  elements  (sensory)  and  the  descending  elements  (motor)  in  the 
complicated  tracts  which  unite  the  covering  of  the  hemisj)heres  to  the  subjacent 
nervous  strata. 

Atrophic  degeneration  is  still  slower  in  appearing,  and  is  less  allied  to  the 
destructive  alterations  M^hich  attack  a  region  of  the  nervous  system  which  is 
of  any  importance.  Not  only  are  the  directly  injured  fibres  altered  in  one  or 
other  direction  (according  to  the  portion  removed),  but  in  the  end  the  nerve 
elements  to  which  the  foregoing  communicate  the  impulse,  ceasing  to  receive 
this  latter  in  sufficient  quantity  or  suitable  qviality,  thems^ves  undergo  a  certain 

degree  of  atrophj-,  as  is 
indeed  the  case  with  all 
parts  of  the  living  body 
when  c  o  n  d  e  m  n  e  d  to 
functional  immobility. 

The  cerebral  cortex 
and  the  optic  thalamus. 
— The  cortex  of  the  brain 
may  be  divided  into  a 
certain  number  of  re- 
gions, each  of  which 
answers  to  one  of  the 
senses.  These  regions 
are  themsehes  capable 
of  subdivision  into  areas 
or  smaller  spaces  which 
correspond  to  distinct 
and  localized  functions 
(which  are  especially  recognizable  in  the  order  of  motor  phenomena).  The 
territorial  divisions  of  the  cerebral  cortex  are  anatomically  and  functionally  re- 
peated in  the  optic  thalamus.  This  is  well  shown  by  those  secondary  degenera- 
tions which  invade  this  ganglion  as  a  consequence  of  limited  destructions  of  the 
surface  of  the  hemispheres. 

The  optic  thalamus  is  formed  of  a  certain  number  of  distinct  nuclei  which, 
according  to  their  position,  are  described  by  the  names  of  ventral,  anterior,  lateral 
and  median  or  internal.  To  these  must  be  added  the  pulvinar,  the  internal  and 
external  geniculate  bodies,  the  mamillary  body  and  the  nucleus  of  Luys. 

Tlie  anterior  and  internal  nuclei  radiate  in  the  frontal  lobe  ;  the  lateral  nuclei 
in  the  parietal  lobe  ;  the  ventral  nuclei  in  the  operculum  ;  the  posterior  portions 
of  the  thalamus,  that  is  to  say  the  pvilvinar,  with  the  occipital  lobe  and  also 
with  the  first  and  second  parietal  lobe  ;  the  internal  genicvilate  boch'  and  the 
posterior  nucleus  with  the  tem])oral  convokitions. 

4.     Functions  of  the  optic  thalamus 

The  functions  of  the  optic  thalamus  were  for  a  long  time  enveloped 
in  the  deepest  obscurity.     Vulpian  acknowledged  that  our  knowledge 


Fig. 


GiiiigHon 

pi.  Fiirroiv 

Pulvinar 


Pineal  gland 
168.— The  optic  thalamus,  the  corpora  quadrigeniina 
tubercles,  the  pineal  gland,  and  the  habenula. 


SUPERIOR  SYSTEMATIZATIONS  411 

on  this  point  was  entirely  insufficient.  Meynert,  whose  inductions 
are  based  especially  on  an  anatomical  foundation,  regarded  this  ganglion 
as  an  important  reflex  centre  ;  but  this  view  was  entirely  wanting 
in  jirecision. 

A.  Clinical  facts. — It  is  to  clinical  observations  that  we  owe  the 
solution  of  this  problem  ;  they  have  shown  us  the  distinction  which 
exists  between  different  kinds  of  motor  paralysis  due,  on  the  one  hand, 
to  lesions  of  the  optic  thalamus,  and  on  the  other  to  alterations  of  the 
cerebral  cortex.     Experiments  have 

also   supplied   data    confirming  this  WsA -.—  oc.  mot.  ». 

distinction. 

1.  Superior  and    inferior    facial. ^ — 

The    facial    muscles,    to    which    are       /  Lj .Sup.fac. 

distributed  the  branches  of  the  facial 
nerve,    may    be    divided    into    two 

regions.     The  first,  superior,  known       \  ^      — ^ Fanain. 

as    the  area  of    distribution  of  the 

superior  facial   nerve,  comprehends         ^^^ X ^inf.fac. 

the  muscles  which  surround  the 
orbital  cavity  (frontalis  muscle,  the 
orbicularis  of  the  eyelids  and  the 
corrugator  supercilii)  ;  the  second, 
inferior,  known  as  the  area  of  the 

.     „      .         „      .    ,  .    .  ,,      Fig.    169. — Superior  and  inferior  facial 

interior  facial  nerve,  comprising  all  (after  Mendel). 

the  other  muscles    of   the   face.       The  The  nucleus  of  the  oculo-motor  governs 

,      .     .      .  ,  all  the  functions  of  ocular  motricity,  includ- 

terms  superior  and  inferior  are  here  j^g  the  opening  and  shutting  of  the  eyelids 
used  only  to  indicate  the  position  of    (^'"^  ^^^^'^'^  ^y  ^''^  p-''^^^  °f  t^^^  superior 

•'  ^  facial). 

the  muscles  in  the  face. 

If,  on  the  other  hand,  the  motor  elements  of  any  particular  nerve 
are  traced  from  the  cortex  to  the  muscles,  it  is  found  that  they  are 
formed  (like  all  otli^'  motor  elements  of  the  same  order)  of  at  least 
two  superposed  neurons.  One  of  these  is  a  deep  neuron,  cortico-bulbar  ; 
the  other  is  peripheral,  bulbo-muscular. 

2.  Deep  and  peripheral  facial. — When  paralysis,  of  whatever  nature, 
attacks  the  peripheral  facial  nerve  (at  its  origin  or  during  its  intra- 
osseous course),  it  scarcely  discriminates  between  its  superior  and 
inferior  elements  mixed  in  the  same  trunk.  The  paralysis  is  then 
called  total,  and  this  both  because  it  affects  all  the  fibres  of  all  the 
facial  muscles  together,  and  also  because  it  suppresses  as  regards  these 
every  source  of  excitation  (voluntary,  instinctive  and  reflex).  It  must 
then  be  considered  as  both  complete  and  radical. 

'  When  paralysis  attacks  the  deep  facial  (either  in  the  cortex  or  its 


412  SYSTEMATIC    FUNCTIONS 

intra-capsular  course),  it  affects  much  more  varied  forms.  This  is  due 
to  the,  anatomically  speaking,  very  well  marked  separation  between 
the  superior  and  inferior  facial  which  is  here  present,  and  also  to  the 
great  variety  of  functions  displayed  by  the  elements  composing  the 
superior  facial  nerve.  Its  situation  in  the  internal  capsule  is  in  the 
anterior  portion  of  the  "  knee  "  of  this  structure. 

In  lesions  of  the  deep  facial  (whether  cortical  or  capsular)  it  seems, 
at  first  sight,  as  though  only  the  inferior  part  of  the  peripheral  facial 
were  paralysed,  the  superior  portion  remaining  immune.  It  is  true 
that  the  features  are  drawn  to  one  side  and  the  corresponding  cheek 
becomes  loose  and  flabby  (so-called  inferior  facial),  while  certain  move- 
ments are  preserved  by  the  frontal  muscles,  and  especially  by  the 
orbicularis  (superior  facial). 

But,  on  examining  the  condition  more  closely,  it  will  be  found  that 
the  superior  facial  does  not  escape  paralysis  ;  it  is  merely  that  this 
paralysis  is  of  a  particular  kind.  In  repose  the  palpebral  opening 
appears  slightly  enlarged ;  this  indicates  a  certain  amount  of  paresis  of 
the  orbicularis  (occasionally  it  is  true,  this  opening  is  found  narrower 
when  the  weakened  muscle  is,  as  sometimes  happens,  the  seat  of  post- 
hemiplegic contractures).  The  folds  of  the  brow  are  unequal  as 
regards  the  two  sides  :  this  also  indicates  a  paresis  or  a  slight  con- 
tracture, according  to  circumstances,  of  the  frontalis  muscle.  Associ- 
ated movements,  such  as  blinking  of  the  eyes,  which  may  be  reflex  or 
involuntary,  are  still  capable  of  performance,  though  more  slowly  on 
the  side  attacked  by  paresis.  But  dissociated  movements,  that  is  to 
say,  the  isolated  occlusion  of  one  eye  on  the  paralysed  side,  are  impossible 
(Pugliese  and  Milla). 

3.  Paralysis  of  the  voluntary  function. — To  sum  up,  in  these  condi- 
tions paralysis  has  not  caused  the  complete  disappearance  of  either 
the  reflex  movements,  the  muscular  tone,  or  even  of  those  movements 
which  become  associated  ones  by  being  involved  with  voluntary  move- 
ments ;  but  it  has  suppressed  certain  locahzed  movements  which  are 
unilateral  and  acquired  by  education,  movements  having,  for  this  reason, 
in  a  high  degree  that  voluntary  character  which  is  opposed  to  the  reflex 
quality,  and  whose  nervous  mechanism  appertains  to  certain  differen- 
tiated areas  of  the  cortex  and  of  its  subjacent  fibres.  In  other  words, 
paralysis  has  in  this  case  attacked  the  voluntary  functions  of  the  deep 
facial,  alloiving  its  reflex  and  emotional  functions  to  remain  unimpaired  : 
it  is  also  possible  for  a  lesion  to  attack  the  latter  without  molesting 
the  former. 

In  hemiplegia  it  may  be  said,  speaking  generally,  that  the  degree 
of  paralysis  of  the  muscles  is  the  more  marked  in  proportion  to  the 


SUPERIOR  SYSTEMATIZATIONS  413 

amount  of  asynergetic  function  possessed  by  them,  that  is  to  say,  the 
more  independent  they  are  of  associations  and  united  action.  As  it 
is  possible  for  these  muscles  to  exercise  different  functions,  one  syner- 
getic  and  the  other  asynergetic,  it  may  also  be  said  that  the  more  in- 
dependent the  function  under  consideration,  so  much  the  more  marked 
is  the  paralysis.  Muscles  may  be  paralysed  as  regards  one  function 
and  continue  active  as  concerns  another. 

The  cortical  region  from  which  the  superior  facial  nerve  arises  is 
situated  in  the  inferior  third  of  the  ascending  frontal  convolution, 
opposite  the  base  of  the  second  frontal.  Its  area  lies  above  those  of 
the  tongue  and  the  mouth. 

Independence  of  movements  acquired  by  education.- — The  orbicular 
muscles  have  (at  least  in  most  people)  acquired  by  education  their 
independent  and  asynergetic  motricity.  In  order  to  see  better  while 
performing  certain  actions,  we  have  formed  the  habit  of  shutting  one 
of  the  eyes,  keeping  the  other  open.  It  is  the  exception  (apart  from 
paralysis)  to  meet  with  subjects  who  are  incapable  of  separately  closing 
one  of  the  eyes. 

The  frontal  muscles  only  contract  synergetically. 

The  corrugator  supercilii  muscles  also  only  contract  together.  How- 
ever, it  is  possible  by  study  and  practice  to  acquire  the  power  of  separ- 
ately contracting  each  muscle  of  the  face  (Sikobsky). 

The  facial  muscles  are  capable  of  performing  reflex  actions,  emotional 
(instinctive)  actions,  and  voluntary  actions.  These  three  kinds  of 
actions  bring  into  play  the  same  muscles  by  means  of  the  same  nerve 
fibres  in  the  peripheral  facial  (bulbo-muscular  fibres).  But,  in  the 
deep  facial,  these  three  orders  of  actions  affect  distinct  and  partially 
independent  systems.  This  is  demonstrable  as  regards  at  least  some 
of  these  actions. 

4.  Voluntary  paralysis  with  preservation  of  the  expression  of  the 
emotions, — Certain  pB,tients  suffering  from  hemiplegia  are  incapable 
of  voluntarily  impressing  any  movement  on  their  paralysed  face  ;  but 
if  they  are  suddenly  seized  by  a  sad  or  gay  emotion,  these  same  muscles, 
though  refractory  to  the  will,  give  an  expression  of  sadness  or  joy  to 
the  face  (A.  Magnus). 

5.  Paralysis  of  the  emotional  expression  with  preservation  of  the 
voluntary  movements. — Conversely  to  what  has  just  been  said,  some 
paralytic  subjects  retain  the  power  of  voluntarily  contracting  the 
muscles  of  the  face  and  of  moving  the  features  ;  but,  should  an  emotion 
unexpectedly  upset  them,  the  face  (perhaps  one  side  only)  is  quite 
incapable  of  revealing  it.  It  may  be  that  at  the  same  time  the  reflex  or 
automatic  movements  of  respiration  are  abolished  (Ch.Bell,  Stromeyer). 


414  SYSTEMATIC    FUNCTIONS 

However,  this  dissociation  is  somewhat  exceptional,  and  paralysis 
may  simultaneously  abolish  the  expression  of  the  emotions  and  of  the 
will  ;  but  w^hen  the  dissociation  exists  it  affords  opportunity  for  an 
interesting  analysis. 

Different  localizations  of  lesions  in  the  two  cases. — Paralyses  of 
voluntary  actions  are  due  to  lesions  of  the  cortex  or  of  the  fibres  of 
projection  directly  connected  with  it  (cortical  and  subcortical  lesions). 
If,  when  these  lesions  exist  the  optic  thalamus  remains  intact,  the  expres- 
sion of  the  emotions  is  still  possible.  The  nuclei  of  the  corpus  striatum 
may  be  injured  or  even  destroyed,  and  so  also  may  the  internal  capsule, 
still  the  result  is  the  same  (Nothnagel). 

B.  Experimental  facts. — According  to  Bechterew,  the  optic 
thalamus  forms  the  chief  centre  or  culminating  point  of  a  particular 
system,  and  is  in  a  certain  degree  independent  of  the  cortico-bulbar 
system  with  which  it  is,  however,  analogous,  though  very  much  more 
simple.  Like  the  cortex,  this  system  is  attached  to  the  medulla  ob- 
longata and  to  the  spinal  cord  by  fibres  of  projection,  both  sensory  and 
motor,  which  are  special  to  it. 

This  system  is  a  reflex  one  :  the  impulses  which  ascend  to  it  from 
the  different  senses  are  here  reflected  as  motor  acts.  These  acts, 
though  automatic,  are  so  in  a  complicated  manner,  and  the  sensation 
of  which  they  are  the  expression  is  an  emotion,  an  instinct. 

The  optic  thalamus,  then,  would  answer  to  a  functional  localization 
of  this  order  ;  it  is  the  principal  locality  for  the  elaboration  of  the 
emotions.  Its  connexions  with  the  cortex  are  numerous  ;  neverthe- 
less, it  may  act  independently.  In  animals,  when  the  cerebral  cortex 
has  been  removed  while  the  optic  thalamus  is  retained,  stimulation  of 
the  organs  of  special  sense  provokes  reflex  movements  of  expression, 
which  are  liable  to  be  mistaken  for  those  of  emotional  expression  such 
as  arise  in  animals  under  sensorial  excitation  of  the  same  nature.  These 
stimuli  cause  grinding  of  the  teeth,  bristling  of  the  fur  or  feathers, 
raising  of  the  ears,  etc.,  all  signs  of  pain  or  anger.  Painful  stimulation 
of  the  skin  will  give  to  the  features  a  hostile  expression.  On  the  con- 
trary, if  the  skin  of  the  back  be  caressed  (in  the  cat),  an  agitation  of 
the  tail  will  result,  and  at  the  same  time  the  purring,  which  in  this 
animal  is  a  sign  of  pleasure. 

Not  only  stimulation  of  the  external  senses,  but  also  of  those  which 
arise  in  the  depths  of  the  organism  as  a  consequence  of  its  general 
wants,  have  analogous  effects  ;  it  is  thus  that  the  sensation  of  hunger 
excites,  in  the  animal  deprived  of  the  cortex,  movements  which  have 
a  relationship  with  nutrition.  The  bird  strikes  the  ground  with  its 
beak,  and  the  guinea-pig  opens  its  jaws  widely.     This  instinctive  move- 


SUPERIOR  SYSTEMATIZATIONS  415 

ment  of  the  jaws  is  observable  in  cases  of  prolonged  inanition  (volun- 
tary) (J.  Soury). 

1.  Motor  tracts  appertaining  to  the  optic  thalamus. — These  instinc- 
tive movements  imply  the  existence  of  motor  tracts  belonging  to  the 
optic  thalamus,  and  which  connect  it  with  the  nuclei  of  motor  nerves 
both  bulbar  and  medullary.  These  paths,  however,  are  still  but  httle 
known  anatomically.  In  any  case,  the  cortico-bulbar  tracts  are  here 
out  of  court,  as  these  comphcated  movements  are  observable  when  the 
pyramidal  tracts,  in  consequence  of  the  removal  of  the  cortex,  are 
entirely  degenerated. 

The  efferent  fibres  of  the  optic  thalamus  (thalamo-bulbar  fibres) 
pass  into  the  upper  stratum  (tegmentum)  of  the  crus  cerebri,  while 
the  pyramidal  fibres  enter  its  lower  stratum  (crusta).  Hence  it  follows 
that  it  is  possible  for  a  sub-thalamic  lesion  of  these  fibres  (in  the  pons) 
to  paralyse  emotional  movement,  just  as  a  sub-cortical  lesion  of  the 
pyramidal  tracts  may  paralyse  a  voluntary  movement  (Huguenin). 
The  destruction  of  the  optic  thalamus  in  animals,  as  in  man,  allows  the 
voluntary  movements  to  persist,  but  entirely  suppresses  all  movements  of 
an  emotional  nature  (movements  of  the  face,  ears,  and,  in  animals,  of 
the  tail). 

2.  Functional  relationship  between  the  cortex  and  the  optic  thalamus. 
— The  functional  distinction  Avhicli  is  apparent  between  the  cerebral 
cortex  and  the  ojjtic  thalamus  does  not  imply  an  absolute  independence 
between  the  first  and  second  of  these  two  systems.  The  anatomical 
connexions  existing  between  them  are  numerous.  It  is  obvious  that 
impulses  are  transmitted  from  one  to  the  other,  and  reciprocally.  When 
both  are  intact  and  their  connexions  maintained,  the  chain  of  psychical 
acts  becomes  longer  and  the  complications  so  much  the  greater.  The 
emotions  may  have  their  starting-point  either  directly  in  the  external 
stimuli,  which  reach  the  organs  of  the  senses  (as  in  the  animal  whose 
cerebral  cortex  has  been  removed),  or  in  the  same  stimuli,  but  by  the 
intermediation  of  the  ideas  and  the  memories  which  they  have  awakened, 
or  left,  in  the  cortical  systems.  Emotion  may  be  brought  into  being 
suddenly  as  the  result  of  remembrance,  that  is  to  say,  without  any 
apparent  immediate  provocation,  but  in  reality  arising  from  an  anterior 
incitement  preserved  in  a  latent  state  in  the  brain. 

Inhibitory  action  of  the  cortex  on  the  optic  thalamus. — The  optic  thalamus  not 
only  receives  impulses  (motor)  from  the  cortex,  but  it  also  experiences  from  it  an 
inhibitory  influence,  which,  when  the  emotion  is  not  too  strong,  prevents  the 
external  manifestations  of  the  latter.  In  hemii^legic  patients  who,  having  lost 
the  power  of  voluntarily  moving  the  facial  muscles,  have  yet  preserved  their 
emotional  motricity,  laughter  or  tears  may  often  be  observed  to  burst  forth  with- 
out any  appreciable  cause,  or  on  the  most  trivial  grounds.     This  is  an  indication 


416 


SYSTEMATIC    FUNCTIONS 


that  the  inhibitory  powers  which  liave  their  seat  in  the  cortex  are  enfeebled,  or 
have  disappeared  (Oppenheim).  This  debiUty  is  naturally  more  pronounced  in 
the  case  of  bi-lateral  lesion  of  the  cortex,  and  it  is  then,  especially,  that  spasmodic 
laughter  and  tears  are  observed. 

With  regard  to  the  mechanism  and  the  precise  seat  of  this  inhibition,  it  must 
be  admitted  that  they  are  far  from  being  known.  Many  hypotheses  may  be 
formulated  on  this  subject.  This  inhibitory  function  might  be  brovight  into 
action  by  means  of  fibres  going  from  the  cortex  to  the  optic  thalamus  itself. 
Some,  like  Oppenlieim,  infer  the  existence  of  cortico-bvilbar  inliibitory  fibres 
which  restrain  the  motor  action  of  the  nviclei  seated  in  the  pons  and  in  the  bulb. 
Any  lesions  in  these  conducting  fibres  would  leave  the  field  open  to  tempestuous 
and  disordered  manifestations  of  the  emotions.      Brissaud  maintains  the  exist- 


Post.  ped. 


Pariet.  fibre. 


Lent,  nucleus 


Ant.  ped. 


Caud.  nudens 


fegtnentam 

Fig.    170. — Diagram  of  the  corona  radiata  of  the  optic  thalamus. 
The  corpora  striata  in  red,  the  optic  thalamus  in  blue  (diagram,  Charpy). 

ence  of  fibres  going  either  to  the  optic  thalamus  or  to  the  grey  substance  of  the 
bulb,  and  believes  them  to  be  situated  in  the  anterior  portion  of  the  internal 
capsule. 

3.  Emotional  reactions  of  the  deep  organs. — Emotion  is  revealed  not 
only  by  movements  of  the  face,  but  also  by  changes  in  the  movements 
of  the  respiration,  by  disturbances  of  the  cutaneous  circulation  and  of 
the  secretion  of  the  lachyrmal  gland,  and,  in  fact,  of  all  the  functions 
of  vegetative  life  which  are  dependent  on  the  great  sympathetic. 
The  optic  thalamus  controls  these  different  functions.  Stimulation 
brought  to  bear  on  the  grey  commissure  of  the  thalamus  causes  secre- 
tion  of   tears,  dilatation  of    the  pupil  ami  exophthalmos.      The    optic 


SUPERIOR  SYSTEMATIZATIONS  417 

thalamus  also   acts   on   the  movements  of  the  heart,  the  stomach,  the 
intestines  and  the  bladder. 

The  optic  thalamus,  to  which  may  be  added  a  certain  portion  of  the 
lenticular  and  caudate  nuclei,  may  be  decomposed  into  a  series  of 
distinct  centres,  whose  stimulation  induces  those  modifications  of  the 
internal  functions  which  are  observable  in  the  display  of  the  emotions 

Christ  iani  has  influenced  the  movements  of  respiration  by  stimulat- 
ing the  floor  of  the  third  ventricle.  Bechterew  and  Mislawsky  have 
noticed  vaso-constriction  and  elevation  of  pressure  to  follow  stimula- 
tion of  the  globus  jjalUdus  and  the  optic  thalamus.  The  same  authors 
have  observed  the  effect  of  stimulation  of  the  different  segments  of 
this  ganglion  on  the  movements  of  the  small  intestine  (strengthening 
by  the  excitation  of  the  middle  region,  weakening  by  that  of  the  ex- 
ternal region).  The  stimulation  of  the  antero-external  region  increases 
the  contractions  of  the  large  intestine  and  causes  defecation.  That  of 
the  inferior  internal  region  near  to  the  grey  commissure  causes  tears 
to  be  secreted.  That  of  the  inferior  part  of  the  anterior  nucleus  causes 
the  bladder  to  contract. 

5.  Functions  of  the  corpus  striatum 

The  corpus  striatum,  amongst  all  the  nervous  organs,  remains  the 
one  whose  functions  are  the  most  obscure. 

Comparative  anatomy  displays  this  ganghonic  mass  in  a  ratio  of 
development  inverse  to  that  of  the  cortex  of  the  brain.  In  osseous 
fishes  this  latter  is  represented  only  by  a  thin  layer  of  epithelial  cells, 
forming  the  roof  of  the  ventricle  of  the  anterior  brain,  which  is  equiva- 
lent to  the  two  lateral  ventricles  of  the  brain  of  mammals.  That  is  to 
say,  in  these  animals  the  cortex  of  the  hemispheres  does  not  exist,  or 
exists  only  as  a  mass  of  grey  matter,  the  cells  which  enter  into  its 
constitution  being  ependymal  elements  like  those  which  line  the  nerve 
cavities. 

Morphological  equivalency  of  the  parts. — The  anterior  lobes  of  the  brain  in 
osseous  fish  are  then  equivalent  to  the  ganglia  of  the  base  (opto-striate  bodies) 
of  mammals  (Rabl-Ruckhard).  A  transverse,  or  interlobar,  commissure  con- 
nects them.  A  basal  bundle,  or  kind  of  peduncle,  is  detached  from  them,  which 
is  formed  of  fibres,  the  first  ascending  (sensory)  the  second  descending  (motor). 
The  axis-cylinder  prolongations  of  the  first-named  form  arborizations  wliich 
come  into  direct  contact  with  the  dendrites  of  the  second,  without  any  inter- 
position of  short  neurons  of  association  ;  or,  at  any  rate,  these  elements  are  few 
in  nmiiber  and  not  very  obvious  (Van  Gehuchten).  The  commissm-e  is  formed 
by  a  dectissation  of  a  portion  of  the  sensory  fibres,  of  which  some  reach  the 
opposite  lobe,  while  others  I'emain  in  the  corresponding  lobe.  This  commissvu'e 
is  in  no  sense  the  equivalent  of  the  corpus  callosum,  seeing  that  the  hemispheres 
are  wanting. 

Functional  non-equivalence. — As  it  is  impossible  to  deny  that  such  animals 

P.  E  E 


418  SYSTEMATIC    FUNCTIONS 

possess,  not  merely  the  facilities  of  instinct,  but  even  a  rudimentary  intelligence, 
we  may  conclude  from  this  that  these  faculties  may  be  exercised  by  nervovis 
organs  other  than  the  brain  properly  so  called,  organs  which  display  a  rough 
sketch  of  it. 

The  basal  bundle,  which  is  easier  to  distinguish  in  batracliia,  manifestly  goes 
from  the  corj)us  striatmn  to  the  spinal  cord  (strio-spinal  tract,  eqvxivalent  to  the 
motor  pyramidal  tract),  while  fibres  ascend  from  the  s^Dine,  the  bulb  and  the 
pons  to  the  corpus  striatum  (equivalent  to  the  sensory  tract).  The  first  descend 
in  the  anterior  columns  of  the  spinal  cord,  and  the  second  may  be  followed  into 
the  antero-lateral  columns  (Van  Gehuchten).  In  these  animals  (batrachia)  a 
rudiment  of  the  corpus  callosum,  and  a  rudiment  of  the  cortex  are  sometimes- 
observable  by  the  appearance  of  a  few  cells  in  the  epithelial  membrane  which 
covers  the  ganglia  of  the  base.  Fibres  of  association  between  the  corpus  stria- 
tum and  the  thalamus,  which  are  well  marked  in  batrachia,  may  also  be  observed. 
Reptiles,  birds  :  development  of  the  cortex. — In  reptiles  an  elementary  sketch 
of  the  cortex  is  observable.  In  birds  the  sketch  is  carried  farther  ;  but  still  only 
exists  as  a  thinnish  membrane.  Still  it  is  possible  to  distingviish  in  this  rudi- 
mentary cortex  five  superposed  layers,  namely  :  the  moleciolar  zone,  a  layer  of 
small  stellate  cells,  a  layer  of  large  stellate  cells  and  of  large  pyramidal  cells 
(that  is  to  say,  cells  of  association  and  cells  of  projection),  a  layer  of  deep  stellate 
cells,  and  finally  an  epithelial  zone. 

An  important  detail  is  that  these  cells  of  projection  which  start  from  the  third 
layer  of  the  cortex,  and  are,  so  far,  few  in  number,  are  not  substituted  for  those 
of  the  corpus  striatrun,  but  merely  added  to  them.  Tlie  corpus  striatum  pre- 
serves its  basal  bundle,  this  latter  retaining  its  relations  with  the  spinal  cord. 

Progressive  building  up  ;   displacement  of  the  directive  functions. — Thus  the 
study  of  comparative  anatomy  enables  us  to  comprehend  the  progressive  building 
up  of  the  nervous  system.     We  see  how  it  establislies  and  completes  each  of  the 
superposed  layers  before  beginning  the  construction  of  the  next  layer,  j^rimary 
ganglia,  spinal  cord,  basal  ganglion  and  cortex.     At  the  same  time  this  super- 
position, althougli  it  may  not  cause  the  disappearance  of  anything  which  has 
already  been  built  up,  does  not  proceed  without  a  certain  fluctuation  between 
these  successive  formations  ;   the  last  comers  seizing  upon  and  develoj)ing  a  part 
of  the  functions  assumed  by  the  primitive  nervous  organs  when  existing  alone. 
The  spinal  cord  and  the  basal  ganglia  lose  their  relative  importance  in  proportion 
to  the  advances  made  by  the    brain    towards    the  preponderating  position  it 
acquires  in  the  hmnan  race. 

Directive  sense,  not  identical  in  all  species. — From  another  point  of  view  the 
brain  itself,  which  owes  its  liigh  functions  to  the  development  of  specific  aptitudes, 
has  not,  in  its  evolution,  always  directed  these  aptitudes  in  tlie  same  manner  in 
all  animals.  Thus  the  psychical  functions  of  one  may  differ  from  those  of  another, 
not  only  in  quantity,  so  to  speak,  but  also  in  quality.  Our  ideas  proceed  from 
our  sensations  ;  but  they  proceed  unequally,  because  our  different  senses  have 
not  an  equal  value,  and  therefore  take  a  very  unequal  share  in  the  formation  of 
ideas.  The  same  thing  occurs  in  tlie  animal  world  ;  only  in  comj^aring  them 
together  it  will  be  found  that  certain  senses,  very  predominant  in  the  one,  may 
be  much  weakened  or  almost  annihilated  in  the  other.  From  this  we  are  forced 
to  a  somewhat  unexi^ected  conclusion,  namely,  that  representations  of  the  ex- 
ternal world  assume  different  forms  in  each  case,  according  to  the  specific  nature 
of  the  sensations  which  are  tlie  original  elements  of  these  representations. 

Sense  of  smell  in  reptiles  ;  vision  in  birds. — In  this  respect  the  comparison  of 
birds  and  reptiles  is  very  significant.  In  the  latter  the  olfactory  sense  has  a. 
preponderating  development  and  is  found,  unlike  the  rest  of  the  senses,  to  be 
connected  with  the  rudimentary  cortex  appearing  in  their  brain.     In  the  first 


SUPERIOR  SYSTEMATIZATIONS  419 

case  (that  of  birds)  it  is  the  sense  of  sight  which  directs  the  reflected  acts  of  the 
animal,  and  this  substitution  is  obviously  necessary  in  beings  which,  by  soaring 
in  the  air,  have  in  a  certain  measure  changed  their  medium.  Further,  in  birds, 
between  the  basal  optic  ganglia  and  the  cerebral  cortex  a  very  important  tract 
will  be  found.  Tliis  tract  is  wanting  in  rejDtiles,  and  in  them  the  principal  con- 
nexion of  the  brain  with  the  superior  centres  is  effected  by  means  of  highly 
developed  olfactory  radiations. 

Physical  and  psychical  elaboration. — A  sense  is  an  assemblage  of  higlily  com- 
plicated functions,  in  wliich  nvumerous  actions  are  concerned.  These  actions, 
by  a  continuous  gradation,  extend  from  the  purely  physical  phenomena  in  which 
they  have  their  origin,  to  the  psychical  phenomena  by  which  they  are  character- 
ized. Tlie  nervous  paths  in  which  each  of  these  acts  is  successively  displayed 
respectively  seciu-e  the  performance  of  these  acts.  It  follows  from  this  that  the 
state  of  perfection  of  a  sense  may  be  considered  from  very  different  points  of  view, 
according  to  which  of  these  actions  is  in  question,  and  especially  as  to  whether 
it  is  their  force  and  physical  precision  or  theu-  psychical  value  which  is  under 
consideration.  The  sense  of  sight  in  a  bird  is  more  piercing  than  it  is  in  a  man  ; 
this  is  due  to  the  fact  that,  not  only  the  globe  of  the  eye,  but  also  the  whole  nervous 
assemblage  which  attaches  it  to  the  sub-cortical  ganglia,  is,  in  the  first-named, 
more  developed  than  in  the  second.  But  man,  from  his  comparatively  imperfect 
visual  sensations,  derives  ideas  and  representations  Avhich  are  absent  in  the  bird, 
because  in  the  cerebral  cortex  he  has  at  his  disposal  a  mechanism  of  transforma- 
tion whose  power  is  infinite  in  comparison  with  that  possessed  by  the  latter. 

In  the  bird  especially,  a  system  of  fibres  is  found,  wliicli  from  the  sub-cortical 
ganglia  returns  to  the  retina  by  a  centrifugal  path,  and  wliich,  though  existing 
in  man  and  other  vertebrate  animals,  is  in  them  much  less  highly  developed 
(Perlia).  The  function  of  these  fibres  which,  although  centrifugal  in  their  nature, 
lead  back  the  nervous  impulse  to  the  sensory  organs  whence  it  aro.se,  is  still  very 
obscui-e.  The  fact  that  the  development  of  these  fibres  is  proportional  to  the 
development  and  the  perfection  of  the  sense  to  which  they  belong  is  a  proof  that 
the  part  they  here  play  is  an  essential  one,  though  but  little  is  known  about  it. 
It  may  be  that  they  have  some  relation  to  the  persistence  of  luminous  impres- 
sions after  their  directly  exciting  effect  has  ceased  ;  or  perhaps  to  the  preserva- 
tion of  these  impressions  in  the  memory  and  the  power  of  re-invoking  them. 

Relations  of  the  corpus  striatum  with  the  anterior  portion  of  the  brain. — Em- 
bryology describes  the  corpus  striatum  as  an  appendage  of  the  fore  brain.  Com- 
parative anatomy  displays  it  to  us  exercising  the  functions  (very  rudimentary 
ones  it  must  be  owned)  of  the  brain  in  beings  (fish)  in  which  the  cortical  covering 
is  still  absent.  In  superior  mammals  the  method  of  degeneration  proves  the 
existence  of  connexions  between  the  cortex  of  the  frontal  lobe  and  the  nuclei  of  the 
corpus  striatum,  principally  the  caudate  nvicleus.  A  cortico-striate  path  exists, 
formed  of  fibres  united  in  small  bundles,  which,  following  the  course  of  the 
internal  capsule,  detach  themselves  from  its  anterior  segment.  These  fibres 
penetrate,  by  preference,  into  the  nucleus  last  spoken  of  (caudate  nucleus),  either 
by  traversing  it  after  giving  collaterals  to  it,  or  by  distributing  themselves  and 
coming  to  a  termination  therein  (Marinesco). 

Analogous  fibres  connect  the  cortex  with  the  optic  thalamus,  and  the  corpus 
striatmn  is  itself  united  to  the  thalamus.  Lastly,  these  nuclei  are  themselves 
attached  by  connecting  fibres  to  the  nuclei  of  the  grey  matter  of  the  pons. 

All  these  paths  are  made  up  of  elements  of  which  some  ascend  and  others 
descend  ;    these  elements  convey  the  impulse  in  one  or  the  other  dii'ection. 

1.  Experimental  data. — As  concerns  the  total  function  appertaining 
to  such  a  system  of  co-ordinated  elements,  and  more  especially  to  the 


420  SYSTEMATIC    FUNCTIONS 

corpus  striatum,  physiology  has  unfortunately  up  to  the  present  time 
remained  but  ill-furnished  with  positive  information. 

Destruction. — Magendie  advanced  the  theory  that,  after  the  removal 
of  the  two  corpora  striata,  the  animal  showed  an  irresistible  tendency 
to  go  forward.  If  this  be  so  the  corpus  striatum  would  possess  functions 
which  are  related  to  the  movements  of  locomotion  and  of  walking. 
The  more  recent  experiments  of  Nothnagel  and  of  Fr.  Rezek  have  led 
these  authors  to  the  same  conclusion.  By  destroying  (with  an  injec- 
tion of  chromic  acid  by  the  aid  of  the  syringe  of  Pravaz)  a  limited 
portion  of  the  caudate  nucleus,  the  first  of  these  authors,  and  also 
Magendie,  succeeded  in  producing  circus  movements,  or  those  of  pro- 
gression in  a  forward  direction  in  rabbits.  Nothnagel  calls  the  area 
of  the  caudate  nucleus  which  is  connected  with  these  movements  nodus 
cursor ius.  According  to  Rezek,  a  relationship  of  the  same  nature 
exists  between  locomotion  and  the  futamen  of  the  lenticular  nucleus. 
It  is  impossible  to  say  what  share  is  taken  in  a  lesion  of  this  kind  by  the 
destruction,  properly  so  called,  and  the  stimulus  which  is  the  result  of 
it  ;  or,  again,  what  part  is  played  by  the  motor  or  inhibitory  elements 
which  are  themselves  destroyed  or  stimulated. 

2.  Supposed  function. — These  grey  masses  of  the  corpus  striatum 
contain  within  themselves  associations  of  sensory  and  motor  elements, 
which  transmit  the  impulse  in  the  desired  manner  so  as  to  secure  the 
performance  by  the  limbs  of  the  movements  by  means  of  which  pro- 
gression is  effected  ;  and,  it  may  be  added,  its  continuance  when  once 
commenced.  These  movements  are  automatic;  or,  to  put  it  differently, 
involuntary.  They  are  produced  by  the  arrival  in  the  system  which  is 
adapted  to  their  performance  of  an  impulse  which  initiates  them.  They 
cease  when  another  impulse  arrests  the  preceding  one  and  brings  the 
automatic  system  back  to  a  state  of  repose  ;  they  continue  during  the 
interval  between  these  two  impulsions.  The  initiation  (or  its  cessation) 
is  alone  voluntary,  and  therefore  the  impulse  which  produces  it  comes 
from  the  cortex,  or  must  have  passed  through  it. 

It  must  not  be  forgotten  that  the  spinal  cord  contains  associations 
which  obviously  effect  co-ordinated  movements.  By  itself  it  can 
cause  the  performance  of  only  the  simplest  of  these,  such  as  swimming 
in  the  duck,  but  not  walking,  which  demands  the  maintenance  of  an 
equilibrium,  itself  alone  representing  a  complex  function. 

Stimulation. — Fran9ois-Franck  and  Pitres  have  not  observed  any 
motor  effect  to  result  from  the  direct  stimulation  of  the  corpus  striatum  ; 
neither  has  Carville  or  Duret  noticed  any  effect  of  this  nature.  Never- 
theless, by  stimulating  the  internal  capsule  of  a  dog  from  which  the 


SUPERIOR  SYSTEMATIZATIONS 


421 


.-•  Int.  cap. 


.  Ext.  C. 


cortical  centre  of  the  anterior  limb  had  been  previously  removed,  and 
of  which  the  corresponding  fibres  of  the  corona  radiata  were  inexcit- 
able,  movements  were  provoked  in  this  hmb,  no  doubt  through  the 
stimulation  of  the  healthy  fibres  coming  from  the  corpus  striatum. 
These  same  authors,  after  having  successfully  removed  the  corpus 
striatum,  observed  a  marked  weakness  of  the  opposite  side  and  a 
special  circus  movement  (probably  due  to  a  lesion  of  the  crura  cerebri). 
If  the  extirpation  is  incomplete, 
contractures  of  the  side  opposite 
to  that  operated  on  are  observ- 
able. These  effects  when  summed 
up  bear  witness  to  the  existence 
of  a  motor  function. 

Lepine  has  seen  pseudo-bulbar 
paralysis  to  be  produced  by  a 
lesion  of  the  pntamen  (labio- 
glosso-laryngeal  paralysis). 

Nucleus  of  Luys  ;  corpora 
quadrigemina  ;  corpora  mam- 
MiLLARiA. — In  the  neighbour- 
hood of  the  optic  thalamus  are 
other  analogous  formations 
which,  like  it,  and  indeed 
often    with    its    assistance,'   are 

capable  of  co-ordinating  into  motor  actions  the  impressions  which 
come  from  the  periphery,  thus  taking  part  in  emotional  and  instinctive 
acts.  As  these  grey  masses  are  more  particularly  connected  with  the 
exercise  of  the  special  senses  (sight,  hearing  and  smell),  their  functions 
will  be  studied  with  regard  to  specific  innervations.  The  sketch  that 
we  are  tracing  hereof  the  progress  of  the  impulses  in  the  nervous  system, 
and  the  functional  modalities  resulting  therefrom,  is  made  by  taking 
as  a  guide  principally  tactile  sensibility  and  the  motricity  of  the  skeleton. 

6,  Instinct  in  man  and  animals 

Man  possesses  reason  and  animals  instinct.  These  two  forms  of 
psychism  sometimes  resemble  each  other  in  a  surprising  manner,  though 
fundamental  differences  at  the  same  time  exist  between  them.  The 
resemblance  is  made  more  marked  by  the  complexity  and  perfection 
shown  in  the  workings  of  instinct.  It  is  also  shown  by  the  certainty 
of  this  working,  which  is  conducted  through  a  series  of  operations  from 
a  given  starting-point  towards  an  end  of  a  useful  nature,  which  is 
steadily  and  inflexibly  kept  in  view  until  attained.     Instinct  not  only 

E  E* 


•^  WhUe  comm. 


Globus  palliJ. 

Fig.  171. — The  three  portions  of  the  ^ 
lenticular  nucleus  of  the  corpus  ' 
striatum. 

Frontal  section,  left  side  (after  Charpy). 


422 


SYSTEMATIC    FUNCTIONS 


directs  the  individual  life  of  animals,  but  in  a  number  of  them  also 
results  in  the  formation  of  social  organizations,  in  some  way  analogous 
to  societies  of  human  beings.  Certain  invertebrata,  like  bees  and  ants, 
are  remarkable  from  this  point  of  view. 

Man,  witnessing  these  acts,  willingly  acknowledges  their  similarity 
to  those  by  which  his  own  intelligence  is  manifested.  The  likeness  in 
the  effect  produced  induces  him  to  admit  a  resemblance  between  the 
psychical  processes  which  are  in  operation  ;  this  resemblance,  how- 
ever, is  merely  a  superficial  one.  It  is  only  necessary  to  place  before 
the  animal  difhculties  easily  overcome  by  human  intelligence  to  mark 
the  difference  which  exists  between  reason  and  instinct. 


Characters  of  instinct. — The  instinctive  act,  like  the  inteUigent  act,  has  its 
starting  point  either  in  an  excitation  or  a  need  {instinctus, 
pricking,  stimulus),  and  resembles  it  also  in  having  a  deter- 
minate end  for  its  aim.  But  in  the  animal  this  aim  is  an 
unknown  one  :  instinct  is  blind.  Intelligence,  on  the  con- 
trary, is  conscious  of  the  end  it  has  in  view,  and  indeed 
forms  an  ideal  representation  of  it. 

Fatality. — The  operations  of  instinct  follow  each  otlier  in 
a  rigorous  order  ;  the  one  gives  rise  to  the  other  without 
contradiction,  inversion  or  complication,  and  all  follow  a 
lineal  series.  They  are  the  realization  of  an  experiment, 
always  the  same  one,  the  internal  and  intra-nervous  deter- 
minism of  which  is  rigid  and  inflexible.  Instinct  has  only 
one  solution  when  facing  the  problem  placed  before  it  ;  in- 
telligence finds  a  great  number.  This  results  from  the 
fact  that,  in  the  human  brain,  particular  antecedent  experi- 
ences have  been  subjected  to  a  methodical  classification.  A 
crowd  of  possible  acts  have  a  parallel  existence  alongside 
the  realized  act,  either  resembling  it  more  or  less,  or  else 
differing  from  it.  Intelligence  knows  the  meaning  of  hesi- 
tation and  doubt,  instinct  ignores  them. 
Innateness,  heredity. — Instinct  is  innate,  its  operations  make  their  first  appear- 
ance at  birth  without  imitation  or  preliminary  education.  That  is  to  say,  with 
Lamarck  and  Darwin,  instinct  is  hereditary.  Anterior  experiences,  brought  into 
action  by  the  animal  from  its  birth,  are  not  really  its  own,  but  those  of  its  an- 
cestors. The  intra-nervous  determinism  which  ensures  their  immediate  realiza- 
tion is  transmitted  from  them  to  it,  by  the  same  route  and  the  same  unknown 
means  as  those  which  secure  the  development  of  its  organs,  and  the  performance 
of  the  functions  by  means  of  which  it  reproduces  a  being  resembling  them  in 
everything.  Further,  it  may  be  said  that  instinct  belongs  to  the  species,  either 
regarded  as  the  aggregate  of  the  beings  forming  it  at  a  given  moment,  or  as  the 
series  of  those  to  be  engendered  in  course  of  time.  Intelligence,  on  the  contrary, 
is  capable  of  acquisitions,  growth,  and  individual  development.  The  inequality 
and  the  variety  of  its  powers  inarks  the  personality  of  the  liuman  indi\idual  ;  the 
animal,  however,  is  no  more  than  a  numerical  unit  in  its  species. 

Relations  with  intelligence. — In  nature  there  are  no  phenomena  so  opposed 
to  each  other  that  it  is  not  possible  to  find  for  them  a  common  basis.  Between 
intelligence  and  instinct  the  difference  is  very  striking,  but  at  the  same  time  their 
relationship  must  be  acknowledged.     In  the  animal,  as  in  man,  instinct  and 


Fig.  172. — Nervous 
system  of  an  as- 
cidian  (after  Car- 
penter). 

a,  mouth  ;  b,  orifice  ; 
c,  ganglion  ;  d,  mus- 
cular bag. 


SUPERIOR  SYSTEMATIZATIONS  423 

intelligence  co-exist  in  extremely  unequal,  bvit  still  recognizable,  clegi'ees.  The 
operations  of  both  are  susceptible,  not  only  of  being  mixed  together,  but  also  of 
being  reciprocally  transformed.  In  man  instinctive  acts  become  rational  ones 
by  progression,  and  acts  of  reason  become  instinctive  by  retrogression  ;  the 
second  of  these  transformations  may  be  advantageous  quite  as  well  as  the  first. 
In  the  directive  part  that  it  assumes  in  us,  intelligence,  in  proportion  as  in  the 
course  of  development  it  reaches  more  elevated  spheres,  entrusts  to  instinct  the 
performance  of  those  inferior  acts  which  have  acquired  their  full  perfection.  In 
the  animal,  the  oj^posite  is  the  case  :  while  instinct  directs  the  series  of  its  acts 
towards  an  vmknown  aim,  intelligence  intervenes  in  the  individual  realization  of 
each  of  them.  The  succession  alone  is  traced  in  advance,  while  the  details  of  the 
operations  often  contain  much  that  is  unexpected. 

Psychical  automatism. — Finally,  intelligence  and  instinct  resemble  each  other 
in  the  complexity  of  their  actions  ;  they  differ  in  the  plasticity  of  the  first  com- 
pared with  the  rigidity  of  the  second.  The  plasticity  of  the  intellectual  processes 
is,  of  all  their  attributes  and  characters,  tlie  one  that  removes  them  fui-thest 
from  physical  or  n^iechanical  phenomena  ;  on  tlie  contrary,  the  rigidity  of  instinct 
is  a  characteristic  which  approximates  it  to  these  jihenomena.  With  the  Car- 
tesian school,  this  likeness  has  been  pushed  as  far  as  an  identification  ;  for  an 
extreme  Cartesian  an  animal  is  an  automaton,  in  the  mechanical  sense  of  the 
word.  Although  this  opinion  no  longer  possesses  any  adherents,  the  exjaression 
is  preserved,  but  it  does  not  now  bear  the  signification  of  a  pvu-e  mechanism. 
Automatism  is  not  incompatible  with  psychism  of  a  determinate  nature  : 
individually  conscious  acts  may  succeed  each  other,  and  be  linked  together  in  a 
Tstrict  manner  (with  or  without  traces  of  memory),  in  the  same  way  as  pvirely 
mechanical  acts.  Fsychical  automatism  is  as  comprehensible  and  as  real  as 
physical  automatism.  An  automatism  of  this  kind  takes  part  not  only  in  instinct, 
but  in  the  intellectual  processes  themselves. 

Comparative  psychology. — When  instinct  and  intelligence  are  studied  in  the 
animal  series,  it  will  be  seen  that,  they  vmdergo  a  progression  which,  if  not  regular 
and  continuous,  is  at  all  events  marked,  in  proportion  to  the  general  develo^jment 
of  this  series.  Instinct  proceeds  from  a  more  elementary  nervous  manifestation, 
namely,  the  reflex,  of  which  it  is  an  elaborated  form.  It  is  impossible  to  deny 
the  existence  of  links  connecting  intelligence  and  instinct,  in  spite  of  the  dis- 
similarities and  contradictions  which  these  two  psychical  modalities  present. 
In  a  similar  way  the  comparative  study  of  the  nervous  systems  is  instructive. 
Reflex  action  is  carried  out  by  a  very  simple  system  of  ganglionic  aspect,  resem- 
bling that  of  the  ascidians.  The  ganglionic  chain  of  the  invertebrata  and  the 
spinal  cord  of  the  vertebjata  (both  considered  separately)  represent  types  of  this 
system  which  are  already  elaborated.  Such  a  system  is  formed  essentially  by 
the  association  of  primary  neui'ons  ;  that  is  to  say,  neurons  proceeding  directly 
from  the  integument  to  the  ganglion  (sensory  neurons),  and  from  the  ganglion 
to  the  muscles  (motor  nevirons),  the  ganglion  itself  being  merely  the  link  of 
association  between  them  (with  or  without  short  neurons  reinforcing  and  com- 
plicating this  association). 

Instinct  is  presided  over  by  superstructures  formed  of  secondary  neurons, 
which  are  not  directly  connected  with  the  integmuent  as  with  the  muscles.  These 
superstructures  proceed,  by  development  and  progressive  extension,  from  the 
short  neurons  of  association  which  already  exist  in  the  ganglia  and  the  segments 
of  the  spinal  cord.  They  form  the  origin  of  the  brain.  The  supra-oesophageal 
ganglia  of  the  invertebrate  chain  have  this  signification.  Their  development  is 
in  relation  to  that  of  instinct.  This  fact  is  more  particularly  demonstrated  when 
a  comparison  is  made  between  the  nervous  systems  of  animals  (insects)  of  the 
same  species,  but  which,  by  being  organized  into  societies,  are  differentiated  for 


424 


SYSTEMATIC    FUNCTIONS 


special  social  functions.  Such  are  the  ants,  amongst  which  the  workers,  a  queen, 
and  the  males  are  distinguishable.  Instinct  progressively  decreases  from  the 
first-named  to  the  last.  The  elaboration  of  the  nervous  system,  however,  still 
continues  in  the  sense  that,  while  the  brain  steadily  diminishes  from  the  workers 
to  the  males,  in  these  latter  the  organs  of  sense  and  the  primary  neurons  are  more 
developed  (Forel). 

The  vertebrata  furnish  us  with  a  new  field  in  which,  as  we  have  seen  above, 
this  comparison  may  be  pursued. 

C.  INTELLIGENCE— THE  BRAIN 
Man  occupies  a  place  by  himself  in  the  animal  world.  His  physical 
weakness  forms  a  contrast  to  the  potency  of  the  means  he  has  been 
able  to  create  for  himself.  He  has  undertaken  the  conquest  of  the 
three  realms  of  nature,  and  endeavours  from  day  to  day  to  bring  them 
more  and  more  into  subjection  to  himself.  Limited  to  an  imperceptible 
space  and  a  momentary  duration  in  time,  he  extends  his  actions  over 
great  distances,  reviews  the  past  and  operates  on  the  future,  thus  pre- 
paring it  in  advance.  This  power  is  the  gift  of  his  intelligence,  which 
reveals  it  in  visible  and  durable  works.  It  may  also  be  added  that 
the  limits  of  this  power  are  nowhere  more  observable  than  in  the  efforts 
made  by  it  to  analyse  the  springs  of  its  own  origin,  and  to  penetrate 
the  secret  of  them.  Like  sensation,  whence  it  is  derived,  intelligence 
is  inseparably  connected  with  organization.     This  organization  is  that 

of  the    nervous 

Epith.  Opt.  thai.  Cere-^e'lum  systcm,    and    in 

i  t  certain  sys- 
tems have  been 
chosen  and  de- 
veloped in  pre- 
f erence  to 
others.  The 
sensory  and 
motor  functions 
of  a  mammal 
differ  but  little 
from  those  of  man.  Every  organ  of  the  special  senses — smell,  sight, 
hearing — may  be  more  developed  and  more  perfect  in  certain  kinds  of 
animals  than  in  ourselves,  and  their  strength  and  motor  agility  maybe 
very  superior  to  ours.  But  the  senses  are  only  instruments  in  the 
service  of  intelligence.  The  factors  of  intelligence  do  not  lie  in  the 
senses  themselves  or  in  the  inferior  system  which  represents  them,  but 
in  an  assemblage  of  superior  systems  controlling  the  former. 

Absolute  and  relative  development. — If,  like  the  organs  of  sense,  we 
compare  the  spinal  cordof  man  with  that  of  mammals,  we  shall  not 


Corpus  striatum 

Fig.   173. — Brain  of  osseous  fish  (after  Edinger). 
The  mantle  is  reduced  to  an  ephithelial  layer. 


SUPERIOR  SYSTEMATIZATIONS 


425 


on.  bulb 

9 


Cerebe'lum 


find  this  organ  more  developed  in  the  former,  but  rather,  on  the  con- 
trary, deprived  of  certain  functions  which  it  has  httle  by  httle  yielded 
up  to  the  brain.  This  last  organ  has,  on  the  contrary,  taken  on  a 
development  striking  even  to  the  least  instructed  eye. 

In  the  animal  world  the  development  of  the  brain  is,  in  a  certain 
way,  connected  Avith  that  of  the  intelligence.  Those  animals  which 
most  nearly  resemble  man  are  provided  with  a  brain  which,  by  its 
dimensions,  its  general  configuration  and  its  principal  divisions,  recalls 
the  human  brain  (primates).  In  other  mammals  this  type  is  modified  ; 
the  structure  tends  to  become  simpler  (carnivora).  This  simplification 
is  very  significantly  expressed  by  the  disappearance  of  the  furrows 
which  bound  the  convolutions  :  the  brain  from  being  gyr encephalic 
becomes  UssencepJialic.  This  degradation  is  the  result,  not  of  an 
uniform  reduction  of  the  different  portions  of  the  brain,  but,  on  the 
contrary,   of 

the  unequal  ^"■'"'^^-  ^^"■'^^-         '*'""'''  ^p'-'"*^ 

develop- 
ment,  or  the 
absence  of 
certain  of 
these  parts. 
Or,  as  may 
perhaps  be 
prefer  able, 
to  consider 
the  matter 
from     the 

opposite  point  of  view,  the  evolution  of  the  nervous  system  is 
effected  by  adding  and  superposing,  little  by  little,  new  systems  to 
those  already  existing,  and  which  are  not  susceptible  of  further  im- 
provement. These  new  systems  give  a  new  value  to  the  organization, 
by  augmenting  the  cohesion  of  the  old  systems  at  the  same  time  that 
they  displace  the  primitive  tie  which  bound  them  together.  In  the 
amphioxus  the  brain  is  scarcely  indicated,  and  the  spinal  cord  fulfils 
the  function  of  a  directive  centre.  In  certain  fishes  the  basal  ganglia 
are  highly  developed,  but  the  cortex  of  the  hemispheres  is  still  wanting 
and  is  only  represented  by  a  non-differentiated  epithelial  ectodermic 
layer.  In  reptiles  this  cortex  begins  to  be  sketched  in.  In  birds  and 
mammals  its  development  continuously  progresses,  and  it  tends  more 
and  more  to  usurp  the  functions  of  the  subjacent  centres. 


Corpus     Opt.N. 
striatum 

Fig.   174. — Brain  of  the  reptile. 
The  mantle  appears  as  nerve  matter. 


Difficulty  of  quantitative  estimations. — This  functional  value,  at  once  both 


426 


SYSTEMATIC    FUNCTIONS 


unequal  and  variable,  of  the  supei'posed  layers  of  the  nervous  system  renders  an 
estimation  of  the  connexion  existing  between  its  development  and  the  elabora- 
tion of  these  functions  themselves  extremely  difficult  to  effect.  No  one  function 
is  enclosed  in  a  circumscribed  segment  of  the  organism  or  of  the  nervous  system  ; 
all  are  in  a  condition  of  mutual  dependence.  The  localizations  of  them  that  we 
can  trace  only  correspond  to  the  cliaracteristic  modalities  of  these  functions,  but 
do  not  include  them  in  their  totality.  The  spinal  cord  is  endowed  with  a  sensori- 
motor fimction,  which  is  a  rough  sketch  of  intelligence.  The  intellectual  function 
of  the  brain  does  not  debar  this  organ  from  possessing  a  senso-motricity,  which 
here  is  not  necessarily  dependent  on  its  highest  psychical  manifestations.  Any 
anatomical  limit  between  the  two  orders  of  functions  is  purely  arbitrary,  difficult 
to  realize,  and  impossible  to  trace. 

It  may  also  be  said  that  animals  differ,  not  only  in  the  degree  of  their  intelli- 
gence, but  also  in  the  apparatus  by  the  aid  of  which  they  maintain,  and  also 
manifest,  that  intelligence.  These  mechanisms  are  those  of  the  senses  and  of  the 
motor  organs  depending  on  them.  In  animal  evolution  the  senses  assvune  an 
unequal  importance,  substituting  and  replacing  each  other  mutually,  but  \^•ithout 
being  equivalent  to  each  other.  A  sense  of  an  inferior  order,  like  the  sense  of 
smell,  having  been  the  fu-st  attached  to  the  rudimentary  brain,  is,  owing  to  this 
act,  found  at  the  very  foundation  of  instincts  and  intelligence.     Superior  senses, 


Fig.   175. — Brain  of  mammal  (after  Edinger). 
Predominating  development  of  the  mantle. 


like  sight  and  hearing,  are,  on  the  contrary,  connected  with  greater  intellectual 
development.  In  animals  of  a  similar  organization,  the  sense  of  smell  may  be 
found  persisting  in  some,  wliile  in  others  it  has  become  atrophied  (osmatic, 
anosmatic). 

Thus  it  is  obvious  that  a  great  number  of  circumstances  help  to  complicate 
the  problem,  and  to  falsify  the  results  of  deductions  which  it  has  been  attempted 
to  draw  in  this  direction.  The  development  of  the  nervous  system,  whether 
estimated  by  its  increase  in  weight,  in  volume,  or  in  the  superficies  of  its  principal 
segments,  depends  on  the  repetition  of  similar  parts,  as  well  as  on  the  addition  of 
new  ones.  It  is  evident  that  the  first  of  these  two  factors  has  no  value  as  regards 
the  development  of  instincts  and  of  intelligence  ;  and  hence  another  difficulty 
arises,  as  it  is  necessary  to  consider  what  share  falls  to  it,  and  then  to  deduct 


SUPERIOR  SYSTEMATIZATIONS  427 

that  share  from  the  numbers  to  be  compared.     All  these  causes  of  error  dispense 
with  the  necessity  of  our  entering  into  a  more  lengthy  examination  of  the  results. 

1 .  Anatomical  data  :  structure  and  connexions 
We  will  now  give  a  summary  review  of  the  organization  of  the  brain 
and  of  its  connexions  with  inferior  systems.  We  will  then  set  forth 
the  results  of  the  experiments  by  means  of  which  efforts  have  been 
made  to  distinguish  its  proper  functions,  by  comparing  them  with 
those  of  the  other  large  segments  of  the  nervous  system.  Afterwards 
we  shall  enter  into  the  analytical  study  of  these  functions  themselves, 
or,  to  put  it  otherwise,  into  that  of  the  functional  locahzations  attribut- 
able to  the  different  regions  of  the  cerebral  cortex  and  its  white  matter. 
On  account  of  its  importance  and  the  numerous  observations  and  ex- 
periments A\dth  regard  to  detail  which  it  permits,  this  study  will  be 
renewed  in  the  second  section  on  the  Systematic  Functions,  in  which 
specific  innervations  are  considered. 

The  grey  matter  of  the  nervous  system  may,  in  the  first  instance,  be 
divided  into  two^  portions  or  two  essential  groups.     One  is  the  grey 
bulbo-medullary  axis  prolonged,  outside  the  vertebral  column,  by  the 
ganglia  of  the  great  sympathetic  and,  in  the  skull,  by  the  optic  thalamus 
and  a  portion  of  the  other  ganglia  of  the  base  of  the  brain.     The  other 
is  the  cortex  of  the  brain,  to  which  a  part  of  the  corpus  striatum  is 
attached.     Fibres  of  projection  unite  the  first  to  the  periphery  by  a 
double  sensory  and  motor  tract  ;   other  fibres  of  projection  enable  the 
two  grey  structures  to  form  junctions  amongst  themselves  by  means 
of  conducting  fibres  which  ensure  a  transmission  in  the  two  directions. 
The  different  stages  or  portions  of  the  first  system  are  bound  together 
by  fibres  of  association.     The  different  areas  of  the  second  are  also 
united  by  fibres  of  the  same  description,  which  here  assume  an  excep- 
tional multiplicity  and  importance.     The  passage  of  these  two  kinds 
of  fibres,  or  their  declissation  from  one  side  of  the  body  to  the  other, 
forms  what  are  known  in  the  two  systems  as  the  commissural  fibres. 
A.  Cortex. — The  layer  of  grey  matter  which  covers  the  brain  is 
described  by  the  name  of  cortex,  paUiu7n,  mantle.     This  superficial 
layer  is  folded  on  itself  in  order  to  form  the  anfractuosities  and  con- 
volutions of  the  brain,  with  the  obvious  aim  of  increasing  its  extent  in 
relation  to  the  bundles  of    white  matter  which  encroach  upon  it  in 
different  directions.     It  entirely  covers  the  two  hemispheres,  except 
in  the  locality  where  they  are  penetrated  by  the  crura  cerebri,  which 
unite  them  to  the  grey  medullary  axis,  and  by  the  corpus  callosum, 
wdiich  connects  the  one  with  the  other. 

When  cut,  the  cortex  displays  a  series  of  stratifications,  visible  to  the 


428 


SYSTEMATIC   FUNCTIONS 


naked  eye  or  with  the  lens,  and  especially  by  transmitted  light  (Bail- 
larger).  Its  histological  study  proves  it  to  be  composed  of  cellular 
elements,  including  several  definite  types  analogous,  if  not  similar,  to 
those  met  with  in  the  spinal  cord,  but  in  greater  variety. 


PI.  of  E'xner 


Slrice  of  Becht. 


Strice  of  Baill. 


liarl.  fibres 


"  Deep  fibres 


"  While  s!i(h. 


Fig.    176. — Cerebral  cortex. 
Diagrammatic  section.    On  the  left,  the  cellular  layers  ;  on  the  right,  systems  of  fibres. — On 
the  extreme  left  a  sensory  fibre  is  seen  ascending. — 1,  2,  3,  4,  the  four  layers  of  cells  ;    2  and  3 
representing  pyramidal  cells  of  differing  size. 

Histologists  have  observed  that  the  structure  of  the  cortex  itself 


SUPERIOR  SYSTEMATIZATIONS 


429 


corresponds  to  a  kind  of  average  type,  which  may  be  found  throughout 
its  extent.  This  type  undergoes  certain  modifications,  according  to 
the  locahties,  some  elements  predominating  in  number  or  in  size  in 
certain  regions,  in  others  effacing  themselves,  and  reciprocally. 


Plumi. 


Structure. — The  superposed  layers  of  tlie  grey  cortical  matter  may  be  reduced 
to  three,  namely  : — 

(1)  The  so-called  molecular  layer. — This  is  composed  of  polygonal,  fusiform, 
and  triangular  cells.  The  fusiform  cells  are  the  most  characteristic  of  this  layer  ; 
they  are  spread  out  in  the  direction  of  the  siu'face  of  the  brain  and  their  prolonga- 
tions, both  protoplasmic  and  those 
of  the  axis  cylinder,  are  limited  to 
this  layer  itself  and  generally  ascend 
towards  the  sm'face  of  the  cortex. 
The  others  are  not  essentially  differ- 
ent. 

(2)  The  layer  of  pyramidal  cells. 
— This  layer  is  double  as  concerns 
some  portions,  triple  as  regards 
others  :  this  is  explained  bj'  the 
fact  that  the  cells  are  increased  in 
size  in  proportion  to  the  depth  to 
which  t  h  e  y  penetrate  (small, 
medimn,  and  lai'ge  pyramidal  cells), 
Avithout  any  abrupt  transition. 

The  pyramidal  cell,  if  not  the 
most  characteristic  element,  is  at 
any  rate  the  one  most  easilj'  recog- 
nized in  the  cortex  of  the  brain. 
The  base  of  the  pyramid  is  turned 
towards  the  white  matter  ;  its  apex 
is  lengthened  above  by  a  principal 
prolongation  (protoplasmic  or  den- 
dritic) up  to  the  molecular  layer  ; 
there  it  spreads  out  into  a  thick 
plume,  bristling  with  short  points 
having  enlarged  terminations. 
From  the  trunk  of  this  principal 
prolongation  shorter  collateral  pro- 
longations are  detached,  these  going 
off  from  the  trvmk  at  a  right  or 
acute  angle.  Lastly,  at  its  base  the 
cell  always  gives  origin  to  basal 
prolongations,  which  are  directed 
laterally  or  obliquely  downwards. 
All  these  prolongations  represent  the  polar  field  by  means  of  which  the  cell 
collects  the  impulses. 

The  axis-cylinder  prolongation  arises  from  the  base  of  the  cell  (rarely  from 
one  of  the  prolongations),  it  plunges  into  and  disappears  in  the  white  matter  of 
the  centrum  ovale.  Before  leaving  the  cortex,  it  gives  off  some  collaterals,  which 
are  there  exhausted.  The  axis-cylinder  prolongation,  however,  descends  and 
sometimes  reaches  very  remote  localities,  for  example  :  the  grey  matter  of 
the  medulla  oblongata  or  of  the  spinal  cord.     From  what  experimental  study 


Brts.  dendrites 


CoUat 


Axis,  eylind. 

Fig.   177. — Pyramidal  cell  of  the  cortex. 
Its  dendrites  in  black  ;       its  axis  cylinders  and 

its  collaterals  in  red. 


430 


SYSTEMATIC    FUNCTIONS 


and  the  degeneration  of  these  nerves  teach  us,  they  may  be  described  as  descend- 
ing or,  in  other  words,  motor  in  fiinction. 

It  must  be  observed  that,  between  these  cells,  others  furnished  with  a  short 
axis  cylinder  exist,  these  representing  what  are  usually  called  elements  of  asso- 
ciation. 

(3)  The  layer  of  polymorphous  cells. — This  layer,  regarded  as  being  double  by 
Meynert,  who  divided  it  into  irregular  cells  and  fusiform  cells,  is  described  as  a 
single  one  by  Cajal,  who  has  given  it  its  new  name.  The  cells  are  ovoid,  fusiform, 
stellate  and  triangular  ;  in  spite  of  their  irregularity,  they  still  have  some  resem- 
blance to  the  preceding  ones.  Their  protoplasmic  prolongations  never  ascend 
up  to  the  molecular  layer,  and  their  axis  cylinder  is  a  descending  one. 
This  layer  also  encloses  somewhat  characteristic  cells,  called  tliose  of  Martinotti, 


Frog 


Lizard 


Fig.    178. — Phylogenetic  and  ontogenetic  evolution  of  the  pyramidal  cell. 
Pyramidal  cell  in  the  frog,  the  lizard,  the  rat,  and  in  man. — a,  b,  c,  d,  e,  progressive  phases 
of  embryological  develojjment  of  the  pyramidal  cell  (after  Cajal). 


whose  ascending  axis  cylinder  mounts  as  far  as  the  molecular  layer,  in  which  it 
spreads  out  longitudinally. 

The  cortex  is  thus  strewn  with  cells  and  traversed  by  fibres.  Of  these  fibres 
some  are  called  radial  and  are  of  the  natiu'e  of  axis  cylinders  of  pyramidal  or 
analogous  cells,  and  others  are  named  tangential  fibres.  Amongst  the  radial 
fibres  some  are  of  great  importance.  These  do  not  emanate  from  the  cells  of 
the  cortex,  but,  on  the  contrary,  from  the  subjacent  regions  of  grey  matter  (par- 
ticularly of  the  bulb  and  the  spinal  cord,  grey  nuclei,  etc.)  whose  axis  cylinders 
are  represented  by  them.  These  fibres,  after  a  journey  of  greater  or  less  length, 
expand  in  the  cortex  up  to  the  molecular  layer,  and  come  into  contact  with  the 
dendrites  of  the  pyramidal  cells.  These  are  ascending  elements  or,  in  other  words, 
sensory. 


SUPERIOR  SYSTEIVIATIZATIONS 


431 


The  tangential  or  transverse  fibres  are  those  which,  cutting  the  cortex  in  a 
direction  perjaendicular  to  the  preceding,  mark  out  by  their  larger  or  smaller 
number  the  strata  which  at  certain  points  are  visible  to  the  naked  eye.  Some 
of  these  are  axis  cylinders  proceeding  in  a  transverse  direction  ;  others,  again, 
are  the  arborizations  of  axis  cylinders,  collaterals  of  gi'eat  length,  like  those  which 
have  been  described  by  Cajal  as  passing  through  the  corpus  callosum  to  the 
opposite  hemisphere. 

To  all  these  elements  maybe  added  the  fibres  forming  the  netuogleia  layer, etc., 
which,  distributed  amongst  them,  in  ignorance  of  their  true  function,  have  been 
called  supporting  elements. 

Local  variations. — In  the  Rolandic  convolutions  an  exaggerated  development 
of  the  pyramidal  cells  has  been  observed  (giant  cells  of  Betz  and  Mershejewski). 
The  body  of  the  cell  is  here  found  to  be  developed  in  proportion  to  the  great 
length  of  the  axons,  some  of  which  descend  as  far  as  the  sacral  region  of  the  spinal 
cord  ;    this  development  is  most  considerable  in  tlie  paracentral  lobule. 

The  occipital  lobe  is  distinguished  by  a  diminution  in  the  number  of  its  striae, 
and  also  by  the  exaggeration  of  one  of  the  latter  which  gives  origin  to  the  stripe 
named  after  Vicq  d' Azyr  or  Gennari.  The  cortex  of  this  lobe  is  rich  in  tangential 
fibres  ;  its  molecular  layer  is,  on  the  contrary,  reduced  and  its  pyramidal  cells 
diminished  in  number. 

An  exaggerated  development  of  certain  tangential  fibres  may  also  be  observed 
in  the  insula  ;  the  anterior  wall  and  the  amygdaloid  nucleus  must  be  considered 
as  portions  of  the  cortex  enveloped  in  the  white  substance. 


CinguJum 


Sup.  I.  tr. 


I'ncif.  tr. 


Inf.  I.  tr. 


Fig.    179. — Diagram  of  the  principal  tracts  of  association  seen  by  transparency  (diagram, 

Charpy). 


Course  of  the  impulse. — These  structural  details  supply"  us  with 
explanations,  if  not  about  the  precise  progress,  at  any  rate  concerning 
the  general  course  of  cerebral  functional  processes. 

The  radial  axis-cylinder  fibres  which  distribute  their  terminations 
in  the  different  layers,  and  more  particularly  in  those  of  the  pyramidal 
cells,  are  the  ascending  paths  which  carry  to  these  cells  impulses  col- 
lected in  the  grey  bulbo-medullary  axis,  where  their  cells  of  origin  and 
their  polar  receptive  field  are  situated.     The  radial  fibres  which  arise 


432 


SYSTEMATIC    FUNCTIONS 


from  the  pyramidal  cells  and  direct  their  axis  cylinders  towards  the 
corona  radiata,  are,  conversely,  those  which  carry  off  the  impulses 
from  the  brain  to  the  grey  bulbo-medullary  axis.  These  are  the  fibres 
which,  on  account  of  their  great  length,  are  called  fibres  of  projection, 
because  the  impulse  is  projected  by  them  to  a  great  distance,  being 
conveyed  from  the  inferior  to  the  superior  stratum  of  the  nervous 
system,  or  reciprocally. 

The  fibres  of  the  corpus  callosum  which  unite  the  two  hemispheres, 
the  longitudinal  fibres  which  join  important  or  distant  lobes  in  each 
hemisphere,  and  the  tangential  fibres  which  unite  the  convolutions 
which  are  more  or  less  near  to  each  other,  are  called  fibres  of  association. 
This  name  has  been  given  them  because  they  associate  distinct  and 
determinate  areas  of  the  brain  in  a  common  function  during  the  per- 
formance of  complicated  cerebral  acts.     Amongst  these  language  may 

be  brought  forward  as  an 
example,  for  in  this  case 
several  senses — hearing  or 
sight — may  alternately  or 
simultaneously  take  part 
in  the  production  of  a 
motor  phenomenon  o  f 
great  significance,  su«h  as 
speech  or  writing.  Still 
shorter  fibres,  following 
either  a  radial,  tangential 

Fig.  180. — Diagram  of  the  arrangement  of  the  qj.      varied    direction,     be- 

fibres  of  projection  and  the  fibres  of  association 

(Charpy).  louging    to    these    local 

cells  of  association,  effect  connexions  between  the  neighbouring  polar 
areas  for  the  performance  of  more  elementary  actions. 

Varied  collections  of  cells,  extending  from  those  which  arise  by  the 
local  association  of  two  or  three  cells,  up  to  those  which  bring  into  play 
large  regions  of  the  cortex,  and  at  the  same  time  render  available  long 
tracts  in  the  sensori-motor  paths,  are  thus  found  prepared  as  tactical 
units  of  a  superposed  and  variable  order,  which  are  rapidly  organized 
or  dislocated  by  the  progressive  fusion  of  the  cells  or  by  their  separa- 
tion, in  order  to  produce  the  formations  corresponding  to  the  very 
different  acts  which  spring  from  the  nervous  functions. 

Human  brain. — We  will  assume  a  knowledge  of  the  position  of  the  fissures 
and  the  convolutions  which  indent  the  surface  of  each  hemisphere,  and  which 
serve  to  divide  it  into  arbitrarily  limited  areas,  to  each  of  which  names  have  been 
given  for  the  purpose  of  identifying  and  recognizing  each  individually  in  case  of 
an  isolated  lesion.     We  will  briefly  call  to  mind  the  deep  fissure  {fissure  of  Sylvius), 


Arc.  fibres 


F.  of  projec. 


SUPERIOR  SYSTEMATIZATIONS 


433 


which,  at>-  the  base  and  laterallj',  separates  the  frontal  from  the  temporal  lobe, 
and  by  its  posterior  branch  divides  the  parietal  lobe  from  the  temporal  lobe  ; 
the  fissure  of  Rolando,  which,  descending  from  the  upper  border  of  the  hemisphere 
towards  the  Sylvian  fissure,  separates  the  frontal  lobe  from  the  parietal  lobe, 
and  the  perpendicular  fissure  or  parieto-occipital  fissvu-e  (scarcely  marked  on  the 
external  surface),  which  separates  the  occipital  lobe  from  the  parietal  lobe,  and 
also  (if  prolonged  in  an  imaginary  manner)  from  the  temporal  lobe. 


,  ,,,,^        .  , ,  •  Crus.  cerebri. 

"t Pom 

■  CerebeHum 
Medulla  oblongata 

Fig.    181. — Human  encephalon  and  its  divisions. 
Side  view  (copied  from  Sehwalbe). 

The  convolution  of  the  corpus  callosum  may  also  be  observed  on  the  mesial 
Eurface  of  the  liemisphere  ;    it  is  inflected  on  this  great  commissm-al  tract  and 


Frontal  lobe  • 


■  'Parietal  lobe 


■Occip.  lobe 


lempural  lobe 

Fig.   182. — Diagram  of  the  convolutions  (after  Charpy). 
Their  grouping  and  their  general  direction  in  man. 

envelops  it  from  its  rostrum  to  its  knee.  The  arch,  open  below,  which  it  forms 
above  the  corpus  callosimi  is  closed  beneath  by  the  second  temporal  convolution. 
This  convolution,  after  terminating  in  a  hook  towards  the  fissure  of  Sylvius, 
forms  an  almost  closed  crow^n  round  the  hilimi  of  the  hemisphere.  We  may  also 
notice  the  limbic  convolution  of  Broca,  whose  relations  to  the  olfactory  tracts  and 
olfactory  bulb  will  be  obvious.  The  remainder  of  the  internal  surface  arranged 
P.  F  F 


434 


SYSTEMATIC    FUNCTIONS 


concentrically  as  a  border  round  the  convolution  of  Hill,  forms  the  internal 
portion  of  the  different  lobes,  whose  limits  are  better  seen  on  the  external  surface. 
Here  may  be  found  the  internal  frontal  (internal  joart  of  the  first  frontal)  ;  tliis 
is  prolonged  beliind  the  origin  of  the  fissure  of  Rolando,  by  the  paracentral  lobe  ; 
it  unites  the  two  Rolandic  convolutions  which  skirt  along  the  fissvu-e  of  that  name. 
Then  comes  the  quadrilateral  lobe  or  pre-cuneus,  an  appendage  of  the  first  or 
superior  parietal.  Then  between  the  perpendicular  external  fissure  (parieto- 
occipital) and  tlie  calcarine  fissure  the  cuneus  belonging  to  the  occipital  lobe. 

Finally,  lower  down,  we  find  the  lingual 
lobe,  a  continuation  of  the  second  tem- 
poral, and  the  fvisiform  lobe,  a  continua- 
tion of  the  first  temporal. 

It  niust  be  borne  in  mind  that  certain 
synonyms  are  einployed.  The  convolu- 
tions which  are  grouped  around  the  fissure 
of  Rolando  are  called  cenfraZ  convolutions. 
These,  more  than  any  others,  have  at- 
tracted the  attention  of  physiologists  and 
clinicians.  The  convolution  by  which 
tliis  fissure  is  bordered  in  front  is  called 
pre-Rolandic  or  ascending  frontal  ;  and 
that  bordering  it  behind,  post-Rolandic 
or  ascending  parietal.  From  the  first  of 
these  are  given  off  in  front  the  three 
frontal  convolutions,  the  third  of  which 
has  special  importance  ;  from  tlie  second, 
posteriorly,  the  two  parietal  convolutions. 
The  two  convolutions  which  border  the 
posterior  brancli  of  the  fissure  of  Sylvius 
are  called  marginal  ;  the  supra-jnarginal 
is  none  other  than  the  second  or  inferior 
parietal  ;  the  infra-marginal  is  the  first  or 
superior  temporal.  The  second  or  inferior 
parietal,  sometimes  called  the  supra - 
marginal  convolution,  which,  being  pro- 
longed behind  tlie  fissure  of  Sylvius, 
twists  round  its  extremity,  also  turning 
round  the  posterior  extremity  of  the  first 
temporal  or  infra-marginal  convolution  and,  bending  so  as  to  retrace  its  steps, 
becomes  continuous  with  the  first  temporal  and  forms  the  pli  courbe  (angular 
gyrus),  an  equally  remarkable  area  of  the  brain  and  one  often  referred  to  in 
cerebral  lesions. 

Brain  of  the  primates  :  monkey. — The  brain  of  the  monkey  is  sufficiently 
like  that  of  inan  for  the  divisions  adopted  in  the  case  of  the  latter  to  be  recog- 
nizable with  tolerable  facility  in  that  of  the  former.  The  same  nomenclatxire 
may  also  be  used  in  both  cases,  at  any  rate  to  designate  tlie  broader  features. 
The  fissure  of  Sylvius,  the  fissure  of  Rolando,  the  perpendicular  internal  fissure 
(parieto-occipital)  continued  externally  by  a  perpendicular  external  fissure,  no 
longer  imaginary  but  strongly  marked,  divide  the  monkey's  brain  into  four  lobes 
{frontal,  occipital,  temporal,  parietal),  all  very  distinctly  defined.  Furrows  divide 
these  lobes  into  convolutions,  of  which  some  are  easy  to  identify  :  the  ascending 
frontal,  bounded  in  front  by  the  arched  furrow  (pre-central),  the  three  other 
frontals  indicated  in  a  confused  manner,  and  the  inferior  parietal,  also  clearly 
bounded  above  by  the  inter-parietal  furrow.     The  insula  is  well  developed. 


tsl 


Fig.   183. — Brain     of     the     dog-faced 
monkey  (left  hemisphere). 

A,  fissure  of  Sylvius  ;  B,  fissure  of 
Rolando  ;  C,  parieto-occipital  fissure  ; 
FL,  frontal  lobe  ;  PL,  parietal  lobe  ;  OL, 
occif)ital  lobe  ;  TSL,  temporo-sphenoidal 
lobe. 

Fi,  supei'ior  frontal  convolution  ;  F'^, 
middle  convolution  ;  F^,  inferior  frontal 
•convolution  ;  sf,  super o -frontal  fissure  ; 
if,  infero -frontal  fissure  ;  ap,  antero- 
parietal  fissure  ;  AF,  ascending  frontal 
convolution  ;  AP,  ascending  parietal 
■convolution  ;  PPL,  postero -parietal  lobule  ; 
AG,  angular  gyrus  or  "  pli  courbe "  ; 
ip,  intraparietal  fissure  ;  T^,  T^,  T^,  tem- 
poro-sphenoidal convolutions — superior, 
middle  and  inferior  ;  t^,  t^,  superior  and 
inferior  temporo-sphenoidal  fissures  ; 
O^,  02,  03^  superior,  middle  and  inferior 
occipital  convolutions  ;  o^,  o^,  first  and 
second  occipital  fissures. 


SUPERIOR  SYSTEMATIZATIONS 


435 


The  striated  monkey,  on  account  of  its  small  size,  is  lissencephalic.  The 
antlu'opoids  (oiirang-outang)  have  a  third  frontal  convolution  which  is  easily 
recognizable. 

Brain  of  the  caenivora  :  dog. — The  brain  of  the  dog,  which  is  frequently 
experimented  upon,  and  taken  as  type  of  that  of  the  carnivora,  requires  a  rather 
more  detailed  description,  as  the  type  to  which  it  belongs  differs  notably  from 
that  of  the  primates  and  of  man.  This  difference  gives  rise  to  great  difficulties 
when  the  question  arises  of  comparing  the  convolutions  of  each,  either  from  a 
fimctional  or  a  morphological  point  of  view. 


ni-o 


Fig.  184. — Brain  of  dog,  superior 
surface  ;  lobes  and  fissures  (after 
EUenberger  and  Baum). 

L.fr,  frontal  lobe  ;  L.p,  parietal  lobe  ; 
L.t,  temporal  lobe  ;    L.oc,  occipital  lobe. 

sy,  fissure  of  Sylvius ;  ec.a,  anterior 
ectosylvian  fissure  ;  ss.m,  middle  supra- 
sylvian  fissui'e  ;  ss.u,  anterior  suprasylvian 
fissure  ;  ss.p,  posterior  suprasylvian 
fissure  ;  a.m,  small  fiurrow  "  en  anse  "  ; 
CO,  coronal  fissure  ;  to,  medio-lateral 
fissxire  ;  ef.{el),  entolateral  fissure  ;  po.  c, 
post -cruciform  furrow  ;  cr,  post -cruciform 
fissure  ;  pr,  presylvian  fissure  ;  jiro,  su- 
perior frontal  fissure  [fissura  prnrea). 


S/zl.p. 


Fig.  185. — Brain  of  dog,  superior  surface 
lobes  and  convolutions  (after  EUen- 
berger and  Baiuu). 

L.o,  olfactory  lobe  ;  L.orb,  frontal  or  orbital 
lobe  ;  fr.a,  anterior  frontal  fissure  ;  jr.p,  posterior 
frontal  fissm-e  ;  fr.med,  middle  frontal  fissure  ; 
pro,  superior  frontal. 

G.sy.a,  anterior  sylvian  convolution  ;  G.ect,  ecto- 
sylvian convolution  ;  G.ect. a,  its  anterior  portion  ; 
g.ss.m,  middle  suprasylvian  convolution ;  G.co. 
{■ss.a),  coronal  or  anterior  suprasylvian  convolu- 
tion ;  fj.ecl,  ectolateral convolution ;  G.ent.  entolateral 
convolution  ;  G.ssp,  suprasplenial  convolution  ; 
Spl.p,  posterior  splenial  convolution  ;  G.ce.p, 
central  posterior  convolution  (post-Rolandic)  ; 
G.ca,  central  anterior  convolution  (pre-Rolandic). 


Superior  surface. — Sulci. — The  superior  sm-face  of  the  dog's  brain  shows  us 
at  first  sight  a  sulcus  in  the  shape  of  a  cross.  This  is  the  inter-hemispherical 
fissure,  which  is  cut  perpendicularly  by  the  crucial  sulcus,  at  the  union  of  its 
anterior  with  its  median  third.  The  last-named  is  the  equivalent  of  the  fissure 
of  Rolando. 

When  the  contoiu*  of  the  hemispheres  is  followed,  the  superior  extremity  of 
the  fissure  of  Sylvius  is  found  to  be  situated  laterally  and  a  little  posteriorly  ; 
this  has  the  same  signification  in  animals  as  in  man. 

The  fissure  of  Sylvius  is  bordered  by  several  sulci  and  concentric  convolutions 
arranged  in  the  form  of  a  horseshoe. 

These  are  (1)  the  fissure  of  Sylvius  itself  ;  (2)  the  ectosylvian  fissure  ;  (3)  the 
suprasylvian  fissure  ;  (4)  the  lateral  fissvu-e.  This  last  is  prolonged  in  front  by 
the  coronary  fissiu*e  and  another  less  important  bifm-cation,  the  fiurow  "  en 
anse." 

On  the  other  hand  there  may  be  observed,  between  the  crucial  fiu-row  and 
the  coronary  fissure,  a  small  fm'row  (post-crucial)  ;    and  in  front  of  the  crucial 


436 


SYSTEMATIC    FUNCTIONS 


fiUTOw  a  more  important  fmTow  (pre-crucial)  ;  lastly,  in  front  of  this  one  two 
other  small  perpendicular  furrows  wliich  form  the  boundary  of  three  convolutions 
at  the  extremity  of  the  frontal  lobe. 

Convolutions. — Immediately  around  the  fissure  of    Sylvius,  and,  as  it  were, 

folded  on  itself,  is  the  Sylvian  convolution 
(consequently  situated  between  the  fissiu'e 
of  Sylvius  and  the  ectosylvian  fissure). 
Around  this  is  the  ectosylvian  convolution 
(between  the  ectosylvian  fissure  and  the 
suprasylvian  fissiire).  The  space  between 
the  suprasylvian  fissm-e  and  the  lateral 
fissTire  is  subdivided  at  its  median  part  into 
two  convolutions  by  a  furrow  (the  ectolateral 
fiu-row).  These  two  are  called  the  supra- 
sylvian and  the  ectolateral  convolutions. 
The  space  situated  between  the  lateral 
fissure  and  the  inter-hemispherical  fissure 
is  also  subdivided  by  a  furrow  (ectolateral 
furrow)  into  two  convolutions,  namely  :  the 
suprasylvian  and  the  ectolateral  convolu- 
tions. 

These  different  sulci  and  convolutions  are 
of  tolerably  large  extent  ;  in  each  and  all  a 
median  portion,  an  anterior  portion  and  a 
posterior  portion  may  be  observed,  accord- 
ing to  the  position  occupied  by  these  parts 
in  the  horseshoe  whicli  they  delineate 
around  the  fissure  of  Sylvius. 

The  fissure  of  Sylvius  is,  as  is  obvious,  a 
very  definite  mark  for  the  description  of 
furrows  and  convolutions  of  the  brain's  s\ir- 
face,  which  siu-round  it  in  a  quadruple  or 
even  sextuple  circuit.  The  crucial  furrow, 
or  fissure  of  Rolando,  serves  equally  well  to 
l^oint  out  very  important  regions.  Imme- 
diately behind  it  is  the  post-Rolandic  or 
posterior  central  convolution  ;  immediately 
in  front  the  pre-Rolandic  or  anterior  central 
convolution.  The  first  of  these  answers  to- 
the  ascending  parietal,  and  the  second  to 
the  ascending  frontal  in  man.  In  front  of 
the  pre-crucial  furrow  which  bounds  the 
pre-Rolandic  convolution,  are  three  pro- 
longed convolutions  following  the  long  axis, 
of  the  brain  and  which  are  more  or  less  equivalent  to  the  three  frontal  convolu- 
tions. 

Insula. — At  the  bottom  of  the  fissure  of  Sylvius  is  an  insula  but  little  developed,, 
consisting  of  two  slightly  marked  folds. 

Many  authors,  amongst  whom  Broca  must  be  reckoned,  do  not  regard  the 
fissure  of  Rolando  as  the  transverse  branch  of  the  crucial  furrow,  but  as  the  pre- 
crucial  furrow  itself  passing  downwards  to  join  the  fissiire  of  Sylvius.  This  view 
is  supported  by  Eberstaller,  who  bases  his  opinion  on  the  fact  that  the  relations 
of  the  pre-crucial  furrow  with  the  insula  are  the  same  as  those  with  the  fissure  of 
Rolando  in  the  jorimates.    Whatever  be  the  value  of  such  reasoning,  which,  even 


Fig.  186. — Brain  of  dog,  its  base, 
its  appearance  as  a  whole,  and 
its  lobes  (after  Ellenberger  and 
Baum). 

a,  olfactory  bulb  ;  a'  external 
branch,  and  a",  internal  branch  of 
the  olfactory  nerve  ;  h,  optic  nerve  ; 
c,  oculo-motor  nerve  ;  d,  pathetic  or 
trochlear  nerve  ;  e,  trigeminal  ;  /,  ex- 
ternal oculo-motor  nerve  ;  g,  facial  ; 
h,  auditory  ;  i,  glosso-pharyngeal  ;  k, 
pneumogastric  ;  I,  spinal  accessory  ; 
m,  hypoglossal. 

1,  olfactory  lobe  ;  2,  anterior  per- 
forated space  ;  3,  transverse  tract 
along  the  anterior  extremity  of  the 
pyriform  lobe  ;  4,  infundibulum  ;  4', 
corpora  quadrigernina  ;  5,  pyriform 
lobe  ;  6,  temporal  lobe  ;  7,  parietal 
lobe  ;  8,  frontal  lobe  ;  9,  pons  ;  10, 
rachidian  bulb;  11,  cerebellum; 
12,  crura  cerebri  ;  1.3,  occipital 
lobe  partly  seen. 


SUPERIOR  SYSTEMATIZATIONS 


437 


from  a  morphological  point  of  view  is  not  particvilarly  definite,  it  would  be  diffi- 
cult in  a  work  on  physiolog\"  not  to  take  into  account  the  functional  characters 
of  the  sulci  and  gyri  so  as  to  compare  them  with  those  of  man  and  the  primates. 
Therefore,  from  this  point  of  view,  the  crucial  sulcus  is  incontestably  the  centre 


Ltl. 


Fig.  187. — Brain  of  the  dog,  lower  sur- 
face ;  lobes  and  fissures  or  f lutovv'S 
(after  EUenberger  and  Bavim)  (*). 


Fig.  188. — Brain  of  the  dog,  lower  sur- 
face ;  lobes  and  convolutions  (after 
EUenberger  and  Baum)  (**). 


(*)  rh,  rhinal  fissure  ;  e,c.a,  anterior  ectosylvian  fissure  ;  ecp,  posterior  ectosylvian  fissure  ; 
ss.p,  posterior  suprasylvian  fissure  ;  sy,  fissure  of  Sylvius  ;  rfe.p,  posterior  rhinal  fissure  ;  s.p, 
sislenial  fissure  ;  o.t,  occipito-temporal  fissure  ;  jo.ay,  sylvian  fossa  ;  ip.r,  pre-sylvian  fissure  ; 
/>•(/,  frontal  lobe  ;   Po,  pons  ;  med.ohl,  medulla  oblongata  ;   Cer,  cerebellum. 

(**)  Olfactory  lobe  removed  from  one  side  to  allow  the  olfactory  fissure  to  be  seen. 
Cerebellum  removed. 

L.G,  olfactory  lobe  ;  L.fr,  frontal  lobe  ;  L.j),  parietal  lobe  ;  L.t,  temporal  lobe  ;  Cer, 
cerebellar  surface  of  the  liemispheres  marked  by  dark  lines  ;  U,  uncus  or  hook  of  the  luppo- 
canipus  ;    Chi,  chiasma  of  the  optic  nerves. 

O.c.a,  anterior  compound  furrow  ;  Sy.a,  anterior  portion  of  the  fissure  of  Sylvius  ;  Sy.'p,  its 
posterior  portion  ;  Ec.p,  posterior  ectosylvian  fissure  ;  Ss.j),  laosterior  suprasylvian  fissure  ; 
Ed,  ectolateral  fissure  ;  Cm.p,  posterior  compound  fissure  ;  olf,  olfactory  fissure  (on  the  right 
of  the  diagram)  ;    spl,  splenial  fissure  ;    spl.p,  post-splenial  fissure. 

of  the  excitable  region  in  the  dog's  brain  (sigmoid  gyrus),  as  the  fissure  of  Rolando 
is  in  that  of  man.  Hence  arises  the  name  of  cen^raZ  con voZwiJons  applied  indiffer- 
ently in  man  and  in  the  dog  to  the  convolutions  grouped,  in  the  first  named, 
around  the  fissure  of  Rolando  ;    in  the  second,  around  the  crucial  sulcus. 

Inferior  surface. — Sulci. — The  inferior  surface,  in  addition  to  the  interhemi- 
spherical  fissure,  shows  us  the  origin  of  the  fissure  of  Sylvius  [Sylvian  fossa)  much 
widened,  and  which,  when  its  borders  are  separated,  allows  the  insula  to  be  seen. 
The  fissure  of  Sylvius,  in  its  progress  to  the  inferior  surface  of  the  hemisphere, 
is  cut  by  a  furrow  extending  from  the  apex  of  the  frontal  lobe  as  far  as  the  occi- 
pital lobe  :  this  is  the  rhinal  fissure.  This  fissure  bifurcates  at  its  posterior 
extremity  into  two  furrows,  the  external  of  which  is  named  the  occipito-temporal 
fissure,  and  the  internal  the  splenial  fissure.  These  fissures  are  indicated  on  the 
cerebellar  aspect  of  the  hemisphere.  Behind  on  the  same  aspect  is  the  post- 
splenial  fissure. 

Convolutions. — -The  fissure  of  Sylvius  separates  the  pyriform  lobe  (an  important 
portion  of  the  temporal  lobe  to  which  belongs  the  uncus  or  hook  of  the  hippo- 
campus) from  the  parietal  and  olfactory  lobes  which  are  anterior  to  it.     The 


438 


SYSTEMATIC    FUNCTIONS 


rhinal  fissure  in  its  anterior  portion  separates  the  olfactory  from  the  frontal  lobe  ; 
and  a  little  farther  on  it  separates  the  olfactory  from  the  parietal  lobe.  Later,  it 
divides  the  pyriform  lobe  into  two  portions,  leaving  the  uncus  inside.  On  the 
lateral  borders  of  the  pyriform  lobe  and  of  the  parietal  lobe  may  be  seen  traces 
of  the  furrows  and  convolutions  of  the  circvimference. 

Lateral  surface. — The  lateral  surface  disjilays  to  us  these  fiirrows  and  convolu- 
tions of  the  circumference  delineated 
around  the  extremity  of  the  fissure  of 
Sylvius.  It  further  displays,  below,  the 
rhinal  fissure  in  its  whole  length  ;  above, 
the  crucial  fiu'row,  the  post-crucial  fur- 
row, and  the  pre-crucial  fxirrow,  which 
joins  the  rhinal  fissure  below.  All  along 
this  furrow  and  the  posterior  part  of  the 
rhinal  fissiu-e  is  a  space  which  separates 
these  two  fissures  from  the  extremities 
of  the  convolutions  of  the  circumference. 
This,  proceeding  downwards  and  pos- 
teriorly, is  called  the  sigmoid  convolution  ; 
anteriorly,  the  composite  convolution, 
and  (behind  the  fissure  of  Sylvius)  the 
posterior  composite  convolution. 

Internal  surface. — The  internal  surface 
is  divided  into  two  bent  parallel  bands 
(almost  as  in  man)  by  a  long  fissm'e  which 
is  itself  bent  round  and  slightly  suggests 
the  calloso-marginal  fissure.  At  the  in- 
ternal part  of  the  frontal  lobe,  this  furrow 
bears  the  name  of  fissure  of  the  knee  of  the  corpus  callosum  ;  at  the  level  of  the 
other  lobes  it  is  called  the  sj)lenial  fissiu'e.  The  splenial  fissure  is  really  nothing 
else  than  the  crucial  sulcus,  which,  from  the  superior  surface  of  the  hemisphere,^ 
descends  along  the  internal  svirface,  then  twists  back  so  as  to  skirt  the  corpus 
callosum  at  a  distance  in  the  same  direction,  ju;it  as  the  furrow  of  the  corpus 
callosum  turns  round  it  in  front.  The  space  separating  it  from  the  corpus  cal- 
losum is  the  convolution  of  the  corpus  callosum  ;  but  below  the  rostrum  of  this 
body  it  becomes  the  convolution  of  the  rostrum  of  the  hippocampus  {gyrus  unci- 
natus).  The  space  comprised  between  it  and  the  border  of  the  lieinisphere  bears 
successively  the  following  names  :  subrostral  convolution  (inferior  part  of  the 
orbital  lobe),  superior  frontal  convolution  (anterior  part  of  this  lobe),  and  pre- 
splenial  convolution  behind  the  crucial  sulcus.  Further  back,  the  margin  is 
subdivided  by  a  fissure  parallel  to  the  splenial  fissure  into  a  splenial  convolution 
and  a  suprasplenial  convolution. 

Limbic  convolution. — The  internal  surface  in  the  dog  (as  in  all  osmatics)  is 
remarkable  for  the  great  development  of  the  limbic  convolution,  and  its  very 
definite  relations  with  the  olfactory  lobe.  According  to  Broca,  under  the 
name  of  "  limbic  convolution  "  is  described  the  convolution  in  the  shape  of  a 
ring  or  a  limbus,  which  is  formed  by  the  convolution  of  the  corpus  callosum 
(supracallosal  portion)  and  the  convolution  of  the  hippocampus  (subcallosal 
part  of  the  limbic  convolution).  The  ring  gives  passage  to  the  corpus  callosum 
and  to  the  crus  cerebri.  Closed  posteriorly  by  the  welding  together  of  the  two 
sub-  and  supracallosal  convolutions,  it  is  in  front  closed  by  the  olfactory  lobe, 
which  sinks  in  it  its  two  strong  roots,  the  outer  one  in  the  first,  and  the  inner  one 
in  the  second,  and  then  continues  it  in  front  as  an  appendage.  The  relations  of 
the  whole  of  this  apparatus  with  the  sense  of  olfaction  in  the  dog  (and  osmatics) 


Fig.  189. — Brain  of  the  dog,  external 
surface  ;  its  appearance  as  a  whole 
and  its  lobes  (after  Ellenberger 
and  Baum). 

1,  olfactory  bulb  ;  2,  its  boundary  by 
the  frontal  lobe  ;  3,  boundary  of  the  frontal 
and  of  the  parietal  lobes  ;  4,  olfactory 
tract  ;  6,  pyriform  lobe  ;  6,  frontal  lobe  ; 
7,  parietal  lobe  ;  8,  temporal  lobe  ;  9, 
occipital  lobe  ;  10.  cerebellum  ;  11,  boun- 
dary between  the  parietal  lobe  and  the 
temporal  lobe  (fissure  of  Sylvius)  ;  12, 
medulla  oblongata. 


SUPERIOR  SYSTEMATIZATIONS 


439 


being  admitted,  it  may  collectively  be  designated  either  by  tlie  name  "  limbic 


rii'i^ 


cm-.p-. 


Fig.    190. — Brain    of    the    dog,    external       Fig.    191  — Brain  of  the  dog,  external  sur- 
surface  ;   fissures  (after  Ellenberger  and  face  ;     convolutions    (after   Ellenberger 

Baiun)  (*).  and  Baum)  (**). 

(*)  Pro,  superior  frontal  fissure;  spr,  subrostral  convolution  ;  /ro,  frontal  fissure  ;  oZ/,  olfactory 
fissure  ;  rh,  rhinal  fissure  ;  rh.p,  posterior  rhinal  fissui'e  ;  pr,  presylvian  fissure  ;  pr.c,  ixe- 
cruciform  fissui'e  ;  p.c,  post -cruciform  furrow  ;  cr,  ciaiciform  fissure  ;  sy,  fissure  of  Sylvius  ; 
ss.m,  middle  suprasylvian  fissure  ;  ss.a,  anterior  suprasylvian  fissm-e  ;  ss.p,  posterior  supra- 
sylvian  fissure  ;  ec.m,  middle  ectosylvian  fissm-e  ;  ec.a,  anterior  ectosylvian  fissm-e  ;  ec.p,  pos- 
terior ectosylvian  fissure  ;  am,  small  furrow  "  en  anse  "  ;  co,  coronal  fissure ;  eel,  ectolateral  fissure  ; 
w,  medio-lateral  fissvu-e  ;  c/,  {ent),  entolateral  fissure  (fissura  confinis)  ;  rh.p.[o.t.),  posterior 
rhinal  fissure  and  occipito-temporal ;    U,  uncus  ;    tro,  olfactory  lobe. 

(**)  Lob.olf,  olfactory  lobe;  Lob.orb,  orbital  lobe;  Pr,  superior  frontal  convolution;  tr.o, 
olfactory  bandalette  ;  U,  uncus  (pyriform  apophysis)  ;  ce.a,  anterior  central  convolution  (pre- 
Rolandic)  ;  ce.p,  posterior  central  convolution  (post-Rolandic)  ;  co.ss.a,  coronal  convolution 
(anterior  suprasylvian)  ;  ec.a,  anterior  ectosjdvian  convolution  ;  sy.a,  anterior  sylvian  convolu- 
tion ;  ec.m,  middle  ectosylvian  convolution  ;  ent,  entolateral  convolution  ;  ss.pl,  suprasplenial 
convolution  ;  m,  marginal  convolution  ;  eel,  ectolateral  convolution  ;  ss.p,  posterior  supra- 
sylvian convolution  ;  ss,  middle  suprasylvian  convolution  ;  sy.p,  posterior  sylvian  convolution  ; 
iolf,  interolfactory  fissure  ;  cm.p,  posterior  composite  convolution  ;  Si,  sigmoid  convolution  ; 
cm. a,    anterior   composite   convolution;    ec.p,  posterior  ectosylvian  convolution. 

lobe,"  or  else  by  that  of  "  olfactory  lobe,"  this  latter  name  being,  however,  often 
reserved  for  its  anterior  enlargement. 

Lobes. — The  brain  of  the  dog  may  be  divided  into  four  lobes    n:ore  or  less 
resembling  those   in  man  ;    and 
to  these  must  be  added,  as  in  all 
osmatics,  a   fifth   lobe,   namely, 
the  olfactory  lobe. 

The  frontal  lobe  is  separated 
from  the  parietal  lobe  by  the 
crucial  sulcus  and  its  external 
prolongation  ;  and  from  the 
olfactory  lobe,  outside  "by  the 
rhinal  fissure,  and  inside  by  the 
fissure  of  the  knee  of  the  corpus 
callosum. 

The  parietal  lobe  is  separated 


G-prs/ifJCSl^^^ 


Cen 


O.ii.S^C 


Fig.  192. — -Brain  of  the  dog,  mesial  aspect,  con- 
volutions and  fissures  (after  Ellenberger  and 
Bavim). 

Cr,  cruciform  furrow  ;  G.pr.spl,  presplenial  convolu- 

from    the    temporal   lobe  by  the  tion  ;   G.ss.pl,  suprasplenial  convolution  ;   G.f,  convolu- 

fissm-e   of     Sylvius  and   its    pos-  t\°'^  °^  the  con^us  callosum    {gyrus  fornieatus);     G.h, 

■^                        .            '■  hippocampal  convolution  ;   G.g,  convolution  of  tlie  knee 

tero-superior  prolongation.  ^j  ^.j^^  corpus  callosum  ;  G.p.spl,  post-splenial  convolu- 

The  occipital  lobe    is    bounded  tion  ;   G.c,  convolution  of  the  cingulum  ;  G.u,  gyrus  un- 

outside        by       the      ectolateral  cinatus  ;     G.u.p,   its  posterior  portion  :    Pro,   superior 

fissm-e,  behind  and  below  by  the  ^^^^f    convolution;    A'.pro,    subrostral    convolution; 

•       f              -1  S'*"'  fissure  of  the  knee  of  the  corpus  callosum  ;    spl, 

splemal  fissure  ;    in    front   it  has  splenial  fissure  ;    Sp.p,  post-splenial  fissure  ;    h,  fissure 

no  definite  boundary.      The  per-  of  the  hippocampus  ;  s.c,  supracallosal  fissure  ;  r,  rostral 

pendicular  internal  and  external  fissui-e ;    crm,    small    cruciform   fissure  ;     G,    knee    of 

fissures  of  the  primates  are  here  *'^f,  "^'■P^   callosum;    Sp,   splenium  of  the  corpus 

.   '■  callosum  ;      C.e,     corpus     callosum  ;      (Jer,     cerebellar 

entirely  wanting.  surface  of  the  brain  ;    ot,  occipito-temporal  fissm-e. 

FF* 


440 


SYSTEMATIC   FUNCTIONS 


The  temporal  lobe,  interpolated  between  the  two  preceding  lobes,  is  bounded, 
on  the  inferior  surface  of  the  brain,  by  the  posterior  rhinal  fissure,  which  separates 
it  from  the  lobe  of  the  corj^vis  callosum. 

The  olfactory  lobe,  prolonged  backwards  by  the  lobe  of  the  corpus  callosum,  is 
separated  externally  from  the  frontal,  temporal  and  parietal  lobes  by  the  rhinal 
fissure  ;  from  the  occipital  lobe,  posteriorly  by  the  splenial  fissure  ;  from  the 
frontal  lobe  within,  by  the  fissure  of  the  knee  of  the  corpus  callosum. 

The  brain  of  the  cat  much  resembles  that  of  the  dog,  but,  while  in  the  dog  the 
lateral  convolution  has  its  greatest  development  in  the  posterior  region,  in  the 
cat  the  anterior  region  is  the  most  developed.  We  may  mention  that,  in  the 
latter,  the  suprasylvian  convolution  containing  the  centre  for  the  movements 
of  the  ears,  is  highly  developed. 

B.  Corona  radiata  ;  internal  capsule,  crura  cerebri.— From 
the  grey  medullary  axis  the  impulse  ascends  to  the  cortex  by  a  direct 
and  indirect  path,  and  redescends  from  it  to  the  grey  axis  in  the  same 


Fig.    193. — Relations  of  the  convolutions  to  the  sutures  of       Fig.    194. — Brain    of    the 
the  bones  of  the  skull,  in  the  dog  (after  Ellenberger  and  rabbit  (Lisseneephalic). 

Baum)  (*).  "  (**) 

(*)   a.  occiput  :    a',    occipital  condyle  ;    a",  styloid  ;    h,   parietal  ;    c,  frontal  ;    d,  sphenoid  ;  e 

temporal  (squamous  portion)  ;  e'  tympanic  bulba  of  tlie  petrous  portion. 
(**)   A,  hemisphere  ;    O,  olfactory  lobe  ;    C,  cerebellum. 

manner.  The  crura  cerebri  formed  by  the  fillet  {ruhan  de  Reil),  en- 
larged by  the  sensorial  and  sensory  elements  which  the  medulla  ob- 
longata supplies  to  it  (ascending  path),  and  also  by  the  pyramidal  tract 
which  is,  in  its  turn,  augmented  by  the  geniculate  tract  (descending 
path),  are  the  direct  route  and  in  every  case  contain  it.  The  superior, 
median,  and  inferior  cerebellar  peduncles,  which  establish  ascending 
and  descending  paths  through  the  cerebellum  between  the  grey  axis 
and  the  cerebral  cortex,  are  the  indirect  path.  Other  elements,  also 
following  an  ascending  and  descending  direction,  furnish  yet  another 
indirect  path  through  the  basal  ganglia  (opto-striate  bodies).  This 
again  follows  the  crura  cerebri,  and  its  fibres  are  arranged  in  a  deter- 
minate area  of  the  thickness  of  the  latter.  The  direct  fibres  are  found 
in  the  locality  called  that  of  the  crnsta  {pied),  and  the  indirect  in  that 
of  the  tegumeyituyn  (calotte). 


SUPERIOR  SYSTEMATIZATIONS 


441 


The  internal  capsule  is  the  layer  of  white  matter  which,  being  a  continuation 
of  the  crui-a  cerebri,  extends  to  the  cerebral  cortex,  intermingling  its  fibres  with 
those  of  the  corpus  callosum  to  form  the  corona  radiata.  It  marks  out  a  passage 
in  the  centre  of  the  hemisphere  between  the  optic  thalanuis  and  the  caudate 
nucleus,  which  are  on  its  inner  side,  and  the  lenticular  nucleus,  which  limits  it 
externally.  By  moulding  itself  on  the  internal  angle  of  the  last  named,  it  assmues 
the  form  of  a  capsule  or  of  a  dihedral  angle,  whose  section  has  the  shape  of  a  set 
square,  and  whose  apex,  directed  inwards,  resembles  the  form  of  an  elbow  or  a 
knee.  The  anterior  limb  of  the  angle  is  that  which  is  called  its  anterior  or 
lenticulo-caudate  segment;  its  posterior  limb  is  known  as  the  posterior  or 
lenticulo-optic  segment. 

The  internal  capsule,  like  the  medullary  roots,  is  a  region  which,  on  account 
-of  its  relative  structural  simplicity,  is  of  gi^eat  interest  to  the  physiologist  and 
the  clinician,  and 
that  interest  is 
also  aroused  by  the 
certainty  and  de- 
terminate charac- 
ter of  the  phenom- 
ena presented  by 
i  t  s  experimental 
lesion,  and  the 
equally  relative 
simplicity  of  their 
interpretation. 

The  roots  pre- 
sent themselves  in 
the  dissociated 
condition  of  con- 
ducting tracts 
devoted,  the  one 
exclusively  to 
sensation  (  p  o  s  - 
terior  roots),  the 
other  exclusively 
to  motion  (anterior 
roots).  The  inter- 
nal capsule  affords  a  new  example  of  a  like  dissociation,  with  the  excep- 
tion that  the  bundles -are  here  not  distinctly  obvious  at  first  sight.  Ex- 
perimental or  pathological  lesions  interrupting  its  posterior  bundles  produce 
a  hemianesthesia  of  the  opposite  side  ;  those  interrupting  its  anterior  portion 
produce  hemiplegia,  also  crossed.  At  first  sight  it  would  seem  as  if  this 
large  layer  of  grey  matter  rej)roduced,  by  condensing  it  at  the  base  of 
the  brain,  the  sensory  field  which  is  distributed  outside  the  spinal  cord 
between  the  posterior  roots  and  the  motor  area  distributed  between  the  an- 
terior roots.  Before  giving  a  description  of  the  important  gradations  by 
which  they  are  distinguished  from  a  fvmctional  point  of  view,  it  will  be  better 
to  determine  their  relative  position  in  a  section  of  the  capsule  perpendicular 
to  the  general  direction  of  its  fibres. 

The  sensory  tract  is  contained  in  the  posterior  portion  of  the  posterior  or  len- 
ticulo-optic segment  of  the  capsule  ;  the  motor  tract  is  contained  in  the  anterior 
part  of  this  same  segment  up  to  and  including  the  knee.  The  anterior  or  len- 
ticulo-caudate segment  of  the  capsule  (in  its  anterior  three-fourths)  is  a  formation 
differing  somewhat  from  the  preceding,  both  as  regards  the  direction  of  its  fibres 


Corona 
radiata 


Occ.  lobe     Call,  fbres 


Cms.  cerebri.     Int.  cap. 


Fig.    195. — Diagi-am  showing  the  internal  capsule  expanding  in 
fan  shape  to  form  the  corona  radiata  (diagram,  Charpy). 
The  lenticular  nucleus  is  seen  on  its  internal  aspect.    The  callosal 
fibres  are  dotted.     The  gangha  which  interrupt  the  fibres  of  the  occi- 
pital lobe  are  not  represented  (rad.  opt.). 


442 


SYSTEMATIC    FUNCTIONS 


Ant.  seymenl 


Lentic.  N. 


Ext.  caps. 


Post,  se-gment    


Retro.  I.  segm. 


Canil.  -V. 


Cart.  air.  Tr. 


Lent.  s^n.  Tr. 


-  O'lif.  peil. 


-  Genie   Tr. 


1 


.  Pyr-  Tr. 


■  ■Sensory  Tr.  {i:ei 


and  tlieir  initial  and  terminal  connexions.     This  subject  will  be  treated  further 

on. 

The  sensori-motor  area  represented  by  the  lenticulo-optic  segment  of  the 
capsule  is  rendered  noteworthy  by  the  fact  that  it  unites  in  a  direct  manner, 
though  at  the  same  time  in  a  descending  direction,  the  two  most  characteristic 
regions  of  the  grey  substance  ;  namely,  the  grey  biilbo-medullary  axis  and  the 
cerebral  cortex.  It  contains  the  fibres  of  projection  which  convey  the  impvilse 
from  one  to  the  other  in  the  two  directions. 

The  motor  area  is  suId- 
divided       anatomically 
into   two    tracts  :      the 
first,    cortico-medullary , 
is  adjacent  to  the  sen- 
sory tract  and  is  called 
pyramidal  from  the  fact 
that,  in  traversing   tlie 
medulla    oblongata,    it 
forms    the   pyramid    of 
this    organ    (its   second 
middle  quarter  answers 
to    the    superior    limb, 
and    its     third    middle 
quarter  to  the  inferior 
limb).      The    second 
cortico-hulbar     adjacent 
to    the    preceding,    i s 
called  geniculate  on  ac- 
count of  its  position  in 
the  knee  of  the  capsule 
(it   corresponds  to    the 
muscles  of  the  face  and 
of  the  tongue).      These 
relations  of  the  cortex 
with     the    spinal    cord 
and  the  medulla  oblon- 
gata   do     not     involve 
essential   differences   of 
function.       But,    further,    other    fibres,    distributed    amongst     the    preceding 
without  forming   distinct  bundles,  descend  from   the   cortex   and  j)roceed  to 
the  nuclei  of  the  pons.     These  are  the  cortico-pontine  fibres  ;   they  represent  a 
particular  kind  of   motricity,   namely  :    the  movement  of  the  head   and    the 
eyes. 

The  sensory  area  is  continuous  with  the  medullary  and  bulbar  nerves  of  general 
sensation.  Further,  in  the  bulb  it  becomes  enlarged  by  the  addition  of  elements 
representative  of  two  new  senses  :  taste  (terminal  nuclei  of  the  glosso-pharyngeal) 
and  hearing  (nuclei  of  the  cochlear  and  vestibular  nerves).  The  fibres  conductive 
of  visual  and  olfactive  sensation  remain  outside  the  path  of  tlie  internal  capsule, 
joining  the  cortex  by  individually  independent  paths. 

Thus  constituted  the  sensory  tract  of  the  capsule  is  none  other  than  the  fillet 
{ruban  de  Reil),  an  assemblage  of  medullary  and  bulbo-cortical  fibres  which  have 
their  origin  in  regions  of  grey  matter  morphologically  differentiated  from  the 
grey  axis,  and  their  terminations  in  distinct  areas  of  the  cerebral  cortex. 

Cortical  fillet  (ruban  de  Reil). — The  sensory  field  is  thus  in  a  certain  sense 
comparable  to  the  motor  field.     Two  neurons,  one  external,  the  other  deeply 


i.> 


■Opt.  thai. 


--'C'aud.  N. 


Opt.  rad. 


Fig.  196. — The  left  internal  capsvile,  horizontal  section. 
Diagram  of  the  tracts —The  motor  tract  and  the  sensory  tract 
are  supposed  to  be  distinct. — The  sensory  path  is  not  direct,  like 
the  motor  path,  but  formed  of  fibres  which  are  interrupted  in 
the  optic  thalamus  and  again  leave  it  in  order  to  reach  the 
cortex. 


SUPERIOR  SYSTEMATIZATIONS 


443 


situated,  form  the  essential  woof  of  the  former  as  well  as  of  the  latter,  and  on 
this  woof  are  woven,  so  to  speak,  innumerable  complications.  However,  this 
apparent  agreement  conceals  extremely  important  differences.  One  of  the  most 
weighty  of  these  is  the  following  :  just  in  the  same  proportion  as  the  relations 
of  the  motor  field  to  the  cortex  are  obvious,  so  are  those  of  the  sensory  field  little 
marked  ;  and  conversely  as  regards  the  optic  thalamus,  those  of  the  fii'st  are 
diffuse  and  little  characterized,  while  those  of  the  second  are  obvious. 


Sensori-motor  Tr. 
{Reil  andpyr.) 


Post,  seg 


Opt.  rad. 
(r.  lent,  sej-.) 


Handle  of  Mey. 


Thalam.  rad. 
(ant.  .segment.) 


Knee 


Head  caudate  X. 
{fusion  of  the  c.  str.) 


,  Genie  tract. 


Fig.    197. — Principal  bundles  of  the  internal  capsule,  and  of  tlie  corona  radiata  (after 

Charpy). 

""-  Left  hemisphere  seen  on  its  mesial  surface.  The  caudate  nucleus  and  the  optic  thalamus 
whose  outline  is  marked  in,  have  been  removed  by  seratcliing.  The  red  line  indicates  the  extent 
of  the  genvi.  The  bundle  of  Meynert,  wliich  is  at  the  same  time  external  and  posterior,  is  in- 
flected in  order  to  proceed  to  the  temporal  region  ;  so  also  is  the  geniculated  tract,  internal 
and  anterior  in  order  to  reach  the  base  of  the  Rolandic  convolutions.  The  anterior  segment  is 
wanting  below,  the  corpora  striata  being  fused  together. 


Under  the  name  of  cortical  fillet  (cortical  ruban  de  Reil)  the  existence  is  main- 
tained of  neui'ons  of  all  lengths,  these  being  the  counterpart  of  the  pyramidal 
and  geniculated  bundles  of  the  motor  field  ;  they  are  present  in  but  small  pro- 
portion. Under  the  name  of  thalamic  fillet  (ruban  de  Reil  de  thalamic(ue)  well 
defined  tracts  are  described  relatively,  which  stop  and  are  reinforced  in  the 
ventral  part  of  the  optic  thalamvis  before  being  carried  on  by  other  neurons  from 
it  to  the  cortex  (Monakow,  Hosel,  Mahaim,  Flechsig). 

In  addition  to  these  medullo-  and  bulbo-cortical  elements,  the  internal  capsule 
is  complicated  by  the  presence  of  inedullo-  and  bulbo-thalaniic  elements,  princi- 
pally sensory,  and  also  by  thalanio-cortical  elements  duplicated  by  fibres  of  con- 
trary direction,  without  taking  into  account  the  analogous  relations  of  the 
corpus  striatum,  and  those  of  these  different  ganglia  amongst  themselves.  Ana- 
tomo-clinical  facts  designate  the  optic  thalanuis  and  its  tlialamo-cortical  riband 


444 


SYSTEMATIC    FUNCTIONS 


(fillet)  as  the  j^ath  most  essential  to  sensation.  Hemiancesthesia  caused  by  lesion 
of  the  internal  capsule  is  never  observable  except  when  the  optic  thalamus  is 
itself  injured  (portion  situated  in  front  of  the  pulvinar),  or  when  the  thalamo- 
cortical riband  (fillet)  is  interrupted  (Long,  These  de  Paris,  1889). 

Experiments. — As  it  is  known  that  the  capsule  represents  an  assem- 
blage of  conductive  fibres  of  very  different  functions,  these  fibres  have 
been  experimentally  interrupted  in  a  more  or  less  isolated  manner. 

Compared  with  that  of  the  posterior  roots,  the  section  of  a  sensory 
tract  is  followed  by  the  same  effects,  which  are  immediately  and  mark- 
edly apparent.  Conscious  sensibihty  is  abolished  in  the  corresponding 
cutaneous  territory  ;  or,  in  other  words,  in  the  opposite  half  of  the 
body  {hemiancesthesia).  In  both  cases  an  external  excitation  no  longer 
reaches  the  cortex,  its  arrival  thither  being  an  essential  condition  for 
the  realization  of  the  phenomena  of  consciousness.  In  the  case  of 
section  of  the  radicular  sensory  neurons  (if  it  were  possible  to  generalize 

it),  every  response  to  external  excita- 
tion would  become  impossible,  all 
the  paths  leading  to  the  grey  sub- 
stance then  being  cut,  and  this  sub- 
stance being  the  place  of  distribution 
of  this  impulse  among  the  motor 
nerves.  The  impulses  which  have 
previously  reached  the  deep  systems 
would  alone  be  able  to  circulate 
there.  In  case  of  section  of  the 
sensory  tract  of  the  capsule,  the 
impulses  collected  by  the  grey  bulbo- 
medullary  nuclei  would  give  rise  by 
their  intervention  to  a  reflex  re- 
sponse which  in  the  former  case 
would  be  an  impossibility  ;  but  the 
cortex  would  no  longer  receive  any 
impulse,  not  even  one  of  an  entirely 
internal  nature,  from  the  grey  me- 
dullary axis. 

Veyssieres,  and  especially  Car- 
ville  and  Duret,  have  performed  ex- 
periments with  the  object  of  separately  cutting  the  component  tracts 
of  the  internal  capsule.  To  reach  this  deep  white  layer  they  employed 
a  trocar  provided  with  an  articulated  blade  which,  when  once  the 
instrument  was  sunk  in  the  brain,  could,  by  means  of  a  spring,  be 
manipulated  from  the  outside  through  the  wall  of  the  skull.     When 


Fig.  198.— Experimental  section  of 
the  internal  capsule  (experiment  of 
Veyssieres  and  of  Carville  and 
Diiret). 

SS,  caudate  nuclei  of  the  corpora  striata  ; 
L,  lenticular  nucleus  ;  P,  pedimcular  ex- 
pansion of  internal  capsule  ;  X,  section 
of  the  peduncular  expansion  which  pro- 
duces hemiplegia  ;  R,  stylet  with  a  spring 
for  performing  section  of  the  internal 
capsule. 


SUPERIOR  SYSTEMATIZATIONS 


445 


Aqueduct         Corp.  quad. 


Grey  rent,  matter 


the  section  is  made  in  the  posterior  portion  of  the  internal  capsule, 
hemiansesthesia  occurs  ;  when  in  the  anterior  portion,  hemiparalysis  is 
the  result.  Yet  certain  reserves  must  be  made  in  accepting  these 
conclusions.  Just  in  proportion  as  the  distance  from  the  roots  is  in- 
creased, and  the  cortex  approached,  so  does  any  distinction  between 
the  elements  of  sensation  and  those  of  movement  become  more  difficult 
to  effect.  Further,  it  is  not  possible  to  guarantee  that  the  optic  thala- 
mus and  its  thalamo-cortical  tract  have  not  been  damaged  by  the 
section.     In  both  cases  the  results  affect  the  opposite  side  of  the  body. 

Crura  cerebri. — When  a  transverse  section  of  the  crura  cerebri  is  affected,  two 
regions  are  distinguishable,  the  one  that  of  the  tegmentum  {calotte)  and  the  other 
the  crusta  (pied).  The  fibres  in  the  region  of  the  crusta  arise  directly  from  the 
cerebral  cortex  without  any  interruption  in  the  central  ganglia,  and  proceed 
from  the  median  sector  of  the 
cortex,  with  the  exception  of 
the  anterior  and  posterior  re- 
gions (Dejerine).  These  fibres 
are  cortico-niedullary  neurons 
(pyramidal  tract),  cortico-bulbar 
neurons  (cerebral  tract  of  the 
motor  cranial  nerves),  cortico- 
pontine neurons  (which  are  called 
the  tract  of  Tiirck,  and  which 
must  not  be  confounded  witli 
the  direct  pyramidal  tract  which 
bears  the  same  name),  and 
finally,  neurons  proceeding  from 
the  cortex  to  the  locus  niger.  The 
radiations  of  the  locus  niger  axise 
especially  from  the  superior 
Rolandic  regions  ;  they  occupy 
chiefly  the  external  two-fifths  of 
the  ci'usta  of  the  peduncle.     The 

cortico-pontine  radiations  proceed  from  all  the  median  sector  of  the  hemi- 
sphere ;  they  occur  mostly  in  the  internal  fovir-fifths  of  the  crusta  of  the  crus 
cerebri. 

The  cortico-medullary  radiations  arise  from  the  Rolandic  operculum  and  from 
the  adjacent  portion  of  the  frontal  operculum  ;  they  traverse  the  knee  of  the 
internal  capsule  and  occupy  the  internal  tract  of  the  crusta  of  the  crus  cerebri. 

The  cortico-medullary  radiations  arise  chiefly  from  the  superior  three-quarters 
of  the  Rolandic  region.  They  pass  through  the  posterior  segment  of  the  capsule 
between  tlie  knee  and  the  retro-lenticular  segment  and  occupy  the  middle  three- 
fifths  of  the  crusta  of  the  cerebral  peduncle,  afterwards  forming  the  bulbar 
pyramid. 

These  different  radiations  thus  individually  occupy  certain  regions  in  prefer- 
ence to  others  in  the  crus  cerebri.  But  they  do  not  form  here  separate  tracts  ; 
on  the  contrary,  they  are  somewhat  profusely  intermingled  both  in  the  crusta 
of  the  peduncles  and  in  the  posterior  segment  of  the  internal  capsule. 

2.  The  psychical  functions  of  the  brain 

The  experiments  of  Flourens  are  of  fundamental  importance  in  the 


j,^  Locus  ni'jer. 


Crusta 


Furrow  jor  tne 
Sub.  perf.  post.        oculo. 
motor  N. 

Fig.    199. — Section  of  the  crus  cerebri. 

The  crusta  is  separated  from  the  tegmentum  by 
the  locus  niger  of  Semering. 


446  SYSTEMATIC    FUNCTIONS 

history  of  the  functions  of  the  deep  nervous  system.  They  portray 
the  question  of  locahzation  in  its  broad  outhnes,  as  is  desirable  in  com- 
mencing the  subject.  These  experiments,  considered  from  this  point 
of  view,  give  a  solution  the  expression  of  which  has  not  greatly  altered. 
But  this  study  is,  and  in  fact  could  only  be,  a  first  approximation. 
The  brain,  with  the  conventional  boundaries  assigned  it  by  anatomy, 
is  not  the  organ  of  a  functional  localization  abruptly  arrested  and  which 
is  superposed  on  these  identical  limits.  On  the  contrary,  it  is  attached, 
both  anatomically  and  physiologically,  to  inferior  systems,  of  which  it 
is  the  elaborated  expression. 

Analysis,  after  having  indicated  the  functional  dissimilitude  existing 
between  the  large  segments  of  the  encephalon,  points  out  their  analogy 
when  it  attacks  them  in  detail,  because  it  finds  them  in  their  turn  to 
be  formed  individually  of  numerous  systems  of  unequal  value,  these 
systems  being  in  a  state  of  transition  from  one  to  another. 

A.  Ablation  of  the  cortex  in  mammals. — Everything  tends  to 
point  out  the  grey  matter  of  the  brain  as  performing  the  most  char- 
acteristic function  of  all  those  devolved  on  this  organ.  On  account  of 
its  superficial  position,  and  in  spite  of  certain  difficulties,  this  portion 
of  the  brain  is  the  most  accessible  to  experiment.  What,  then,  we  may 
ask,  will  be  the  modifications  of  the  nervous,  motor,  sensory,  sensorial, 
physical,  etc.,  functions  in  an  animal  whose  cortex  has  been  removed 
as  completely  as  possible  ? 

1.  Scheme  of  the  experiment. — The  leading  idea  of  the  experiment 
was  to  leave  intact  all  the  organs  of  the  senses  in  connexion  with  the 
grey  sub-cortical  masses,  but  to  entirely  destroy  the  cortical  matter 
itself,  and  then,  by  the  modification  thus  induced,  to  infer  the  functional 
value  of  the  cortex  which  has  been  removed. 

Goltz  was  able  to  carry  out  this  experiment  on  a  dog  and  afterwards 
to  keep  the  animal  alive  during  eighteen  months.  The  project  was, 
however,  only  approximately  realized  ;  but,  nevertheless,  as  far  as  it 
goes,  in  an  adequate  manner. 

Operative  results. — The  removal  of  the  cortex  (effected  in  several  operations) 
was  not  entirely  complete.  It  was  neces.sary  to  spare  the  uncus  on  both  sides  so 
as  not  to  injure  the  optic  nerves,  therefore  a  portion  of  the  cortical  giistatory 
area  remained.  On  the  contrary,  the  external  geniculate  body  was  involved 
on  the  left  side,  wliich  entailed  a  degeneration  of  the  anterior  corpus  quadri- 
geminum  and  of  the  corresponding  ojatic  thalamus.  The  sub-cortical  visual 
apparatus  was  thus  destroyed  on  one  side,  but  retained  on  the  other  as  a  control 
of  the  visual  functions  (there  was  persistence  of  the  pupillary  reflex  to  light).  The 
olfactory  lobes  were  in  part  retained.  It  must  be  noted  further  that  the  removal 
of  the  cortex  gave  rise  to  secondary  degenerations  in  the  corpora  striata  and  the 
optic  thalami,  both  of  these  being  attacked  with  softening. 


SUPERIOR  SYSTEMATIZATIONS  447 

Great  care  was  taken  at  first  to  forcibly  feed  the  animal,  as  it  refused  all  nourish- 
ment,-and  only  began  to  accept  it  on  the  twenty-third  day. 

State  of  the  senses. — The  sensory  and  sensorial  functions  in  this 
animal  did  not  completely  disappear  ;  in  fact,  on  a  superficial  examina- 
tion, they  might  have  been  considered  to  have  been  preserved.  The 
animal  closed  its  eyes  at  the  approach  of  a  bright  light  ;  a  paw  brought 
into  contact  with  cold  water  was  instantly  withdrawn.  Pinching  of 
the  skin,  insufflation  of  air  into  the  external  ear  or  over  the  eyes  pro- 
voked defensive  movements.  Annoyed  by  such  stimulations,  the 
a,nimal  barked,  growled,  and  tried,  but  unsuccessfully,  to  bite.  A  loud 
and  prolonged  noise  awoke  it,  and  even  provoked  defensive  movements. 
Nothing  definite  was  noticed  concerning  the  sense  of  smell  ;  but  food, 
accepted  and  swallowed  if  it  had  its  normal  qualities,  was  rejected  when 
impregnated  with  a  bitter  substance.  When  its  fast  was  prolonged, 
the  animal  walked  without  cessation  in  all  directions  in  its  cage,  put- 
ting out  its  tongue  in  a  rhythmical  manner.  When  its  food  was  put  in 
front  of  it,  it  drank,  ate,  and,  once  its  hunger  satisfied,  slept. 

Nutrition. — The  quantity  of  food  necessary  to  maintain  it  in  good 
condition  was  considerable,  1,000  grammes  of  meat  and  500  grammes 
of  milk  for  a  dog  weighing  5  kilos.  A  rather  large  loss  occurred  by  the 
fseces  ;  and,  on  the  other  hand,  the  skin  was  generallv  very  warm, 
indicating  that  the  animal  lost  large  quantities  of  heat. 

The  urine  was  normal  ;  the  excreta  had  the  usual  appearance. 
Digestion  and  the  functions  of  nutrition  in  general  were  carried  on  in 
the  normal  manner. 

Instincts,  emotions. — The  sexual  instinct  was  destroyed.  The  animal 
did  not  of  itself  show  any  emotion,  either  gay  or  sad  ;  it  did  not  answer 
by  any  sign  to  caresses,  menaces,  calls,  or  to  the  sight  of  other  animals. 

2.  Earlier  experiments. — This  description  differs  from  that  which  is 
usually  given  of  an  animal  deprived  of  its  cerebrum,  according  to  the 
account  of  Flourens.  Nevertheless,  the  principal  features  persist,  and 
the  resemblance  is  maintained,  thanks  to  some  re-touching.  Like  the 
pigeon  described  by  Flourens,  the  dog  of  Goltz  deprived  of  its  cerebrum 
does  not  seek  its  food  for  itself,  even  when  it  is  pinched  by  hunger  ; 
it  merely  accepts  it  when  placed  before  it.  The  principal  instincts, 
the  emotions,  the  intelligence  properly  so  called,  have  disappeared. 
The  movements,  unquestionably  very  complicated,  that  the  aniinal 
deprived  of  its  cerebrum  is  capable  of  performing  have  hardly  any  spon- 
taneity ;  they  are  the  response  to  an  immediate  provocation,  consisting 
in  external  excitations  of  the  senses  of  hearing,  sight  and  touch  .  .  . 
or  in  internal  excitations  of  the  kind  to  w^iicli  hunger  gives  rise.     It  is 


448  SYSTEMATIC    FUNCTIONS 

remarkable  that,  under  the  influence  of  these  latter,  the  animal  performs 
all  the  movements  requisite  for  nutrition,  including  the  prehension  of 
food. 

Psychical  images. — After  removal  of  the  cortex,  the  animal  com- 
pletely loses  the  benefit  of  those  anterior  impulses  sloAvly  warehoused 
and  preserved  by  the  brain  under  the  form  of  what  are  called  cerebral 
images.  These  cerebral  images,  persisting  in  the  mind  after  the  with- 
drawal of  the  object,  superpose  themselves  on  the  present  or  actual 
image  of  that  object,  and,  being  mutually  associated  in  different  ways 
and  circumstances,  end  by  attributing  to  it  a  symbolical,  that  is  to  say, 
a  synthetic  value.  The  crack  of  a  whip  will  draw  cries  from  the  animal, 
and  will  provoke  reactions  of  a  defensive  nature  ;  the  sight  of  the  whip 
will  make  no  impression  upon  it,  because  it  no  longer  awakens  the 
image  or  remembrance  of  anterior  sensations  experienced  by  means 
of  this  same  object. 

Not  only  is  the  store  of  co-ordinated  impulses  under  the  form  of 
acquired  knowledge  or  complex  images  annihilated,  but  the  power  of 
re-acquiring  knowledge  of  the  same  nature  no  longer  perceptibly  exists. 
For  months  the  animal  deprived  of  the  cerebrum  may  be  taken  out  of 
its  cage  at  the  time  of  meals,  and  for  months  this  manipulation  wiU 
provoke  its  anger,  because  it  is  incapable  of  recognizing  a  connexion 
between  the  action  and  the  meal  which  it  desires,  or  the  hunger  from 
which  it  suffers. 

Partial  re-education. — However,  though  the  animal  is  condemned 
to  profound  and  irremediable  decadence,  yet  facts  tend  to  show  that 
it  is  nevertheless  susceptible,  in  a  small  measure,  of  a  partial  re-educa- 
tion as  regards  those  nervous  functions  which  are  the  most  directly 
connected  with  nutrition.  Immediately  after  the  operation  deglutition 
is  extremely  difficult,  and  prehension  of  food  is  abohshed.  These  two 
functions,  however,  are  in  the  end  normally  performed  ;  the  former 
being  first  re-acquired,  and  the  latter  at  a  later  date.  This  indicates 
the  culminating  point  in  the  secondary  education  of  the  animal.  The 
mechanism  by  which  these  faculties  are  re-acquired  is  capable  of  several 
explanations.  There  may  have  been  merely  an  arrest  of  the  functions 
of  the  sub-cortical  nervous  masses  caused  by  the  shock  of  the  operative 
lesion  ;  this  hypothesis  is  the  one  to  which  Goltz  gives  his  adhesion. 
According  to  this  author,  it  may  be  possible  that  the  functions  of  those 
masses  which  are  phylogenetically  and  ontogenetically  anterior  to  the 
brain  itself,  and  which,  for  this  reason,  have  at  first  performed  the 
cerebral  functions,  but  which  in  the  developed  animal  are  only  exer- 
cised in  concert  with  the  brain  and  under  its  direction,  may,  by  means 
of  the  repetition  of  excitations  terminating  in  them,  re-acquire  their 


SUPERIOR  SYSTEMATIZATIONS  449 

primitive  development  and  once  more  take  upon  themselves  the  func- 
tion of  directive  systems,  after  the  loss  of  those  from  which  they  had 
previously  received  this  direction. 

In  any  case  the  conclusion  to  be  drawn  is  that,  in  order  to  explain 
the  aptitudes  retained  by  the  animal  after  the  loss  of  its  brain,  it  should 
be  examined  not  onl}'  in  the  days  immediately  following  the  operation, 
but  again  after  as  long  a  delay  as  possible  ;  it  being  probable  that  the 
results  obtained  after  this  delay  will  notably  differ  in  some  respects 
from  those  previously  observed. 

3.  The  cerebral  cortex  and  sensation. — In  the  animal  deprived  of 
its  cerebrum  stimulation  of  the  senses  provokes  co-ordinated  responsive 
movements,  these,  however  no  longer  having  the  value  of  what,  in 
ordinary  language,  are  called  intelligent,  or  even  instinctive  acts,  but 
displaying  nevertheless  a  marked  adaptation  to  the  stimulation  itself. 
This  adaptation  is  so  striking  that  the  movements  have  been  named 
defensive  reactions.  Are  these  excitations  felt  ?  Quite  lately  the 
nervous  phenomena  of  the  reception  of  impulses  were  divided  into  two 
categories,  the  characteristic  of  the  one  being  the  sensation  by  which 
they  were  accompanied  ;  and  of  the  other,  the  absence  of  that  sensation. 

The  nervous  act  in  the  first  case  is  conscious-voluntary  ;  in  the 
second  it  is  called  reflex  or  automatic,  and  by  this  is  meant  that  its 
nature  remains  entirely  mechaiikal,  while  in  the  first  it  has  a  psychical 
character.  Further,  the  doctrine  seems  pretty  firmly  established  that 
nervous  phenomena  must  belong  either  to  the  first  or  second  of  these 
two  categories,  according  to  their  localization  either  witliin  or  outside 
the  cerebral  cortex. 

Cortical  reflexes. — This  expression  is  much  too  simple,  and,  above 
all,  too  exclusive.  The  participation  of  the  cortex  is  doubtless  neces- 
sary in  acts  of  an  evident  and  well-defined  psychical  character.  This  is 
explained  by  the  fact  that,  owing  to  its  predominant  situation  and  its 
complicated  structiu*e,-the  cortex  alone  is  adapted  to  the  realization 
of  these  phenomena  of  synthetic  nature,  no  other  region  of  the  grey 
matter  being  capable  of  effecting  this  synthesis  in  the  same  degree. 
But  this  aptitude  does,  not  exclude  it  from  participation  in  phenomena 
of  a  simpler  and  apparently  automatic  or  reflex  order.  Everything 
depends  on  the  number,  the  value,  or  the  individual  complexity  of  the 
systems  which  are  associated  for  the  performance  of  the  act  to  be 
carried  out,  this  act  being  either  of  a  simple  nature,  such  as  the  winking 
of  the  eyehds,  or  proceeding  gradually  upwards  in  the  scale  until  a 
complicated  action,  such  as  premeditated  speech,  is  attained.  All 
these  acts,  though  of  such  unequal  value,  may  imply  the  participation 
of  the  cerebral  cortex. 

p.  G  G 


450  SYSTEMATIC    FUNCTIONS 

The  sub-cortical  systems. — The  sub-cortical  systems  take  part  in  a 
large  number  of  apparently  automatic  and  reflex  acts,  which  they  are 
capable  of  performing  without  the  aid  of  the  cortex.  The  determina- 
tion of  this  fact  has  been  the  origin  of  a  generalization  resembhng  the 
preceding  one  ;  reflex  phenomena  have  therefore  been  attributed  to 
these  systems  in  almost  as  exclusive  a  manner  as  consciousness  has 
been  reserved  for  the  cerebral  cortex. 

Gradation  of  the  psychical  phenomena. — So  absolute  an  opposition 
is  justified  neither  by  the  facts  of  anatomy  nor  of  physiology.  The 
authentication  of  nervous  acts,  some  quite  rudimentary,  while  others 
have  attained  their  greatest  development,  ought  not  to  cause  us  to 
forget  the  intermediate  series  connecting  the  first  with  the  second.  It 
is  the  acts  belonging  to  this  state  of  transition  which  are  brought  into 
strong  relief  by  the  experiment  of  Goltz. 

4.  Sensations  which  have  undergone  reduction. — Sight,  hearing, 
touch  and  taste  in  an  animal  deprived  of  its  cerebrum  are  certainly 
considerably  reduced,  compared  with  the  acuteness  of  these  senses  in 
the  normal  animal.  We  may  add,  that  it  is  difficult  to  say  which 
elements  belonging  to  each  of  these  senses  have  suffered  this  reduction  ; 
but,  as  Goltz  remarks,  it  would  be  still  more  difficult  to  deny  sensations 
to  an  animal  in  this  condition,  since  the  criterion  which  we  employ 
to  authenticate  them  in  animals  in  a  normal  state,  that  is  to  say,  special 
motor  reactions  (specific  in  a  sense)  by  means  of  which  they  are  revealed 
to  us,  still  persist  in  it.  Intelhgence,  knowledge,  instinct,  are  complex 
facts,  into  which  sensations  enter  as  component  unities  or,  as  they  are 
sometimes  called,  elements.  This  element  itself  is  not  a  simple  one, 
being  produced  as  it  is  by  functional  associations  which  necessitate  a 
systematization  of  the  nervous  cellular  activities. 

The  experiment  of  Goltz,  the  removal  of  the  cortex,  brings  into 
existence  a  systematization  from  which  knowledge  and  intelhgence 
have  disappeared,  but  one  that  is  still  capable  of  developing  crude 
sensation  furnished  with  a  character  which  endows  it  with  a  sufficient 
resemblance  to  the  clear  and  highly  differentiated  sensation  serving 
as  a  comparison.  Further,  this  doctrine  is  not  a  new  one.  Longet 
and  Vulpian  noticed  that,  after  the  removal  of  the  brain  down  to  the 
pons,  but  not  including  the  latter,  a  sensory  stimulation  may  be  fol- 
lowed by  emotional  reactions  on  the  part  of  the  animal  thus  mutilated, 
the  character  of  these  reactions  having  convinced  them  of  the  existence 
of  a  crude  sensation  which  is  quite  opposed  to  that  entirely  conscious 
sensation,  the  development  of  which  necessitates  the  intervention  of 
the  hemispheres.  The  experiment  of  Goltz,  by  allowing  of  the  survival 
of  the  animal,  is  more  striking  and  more  decisive  :   it  also  lends  itself 


SUPERIOR  SYSTEMATIZATIONS  451 

better  to  psychological  analysis.  And  as  it  differs  with  regard  to  the 
destructions  brought  about,  it  serves  to  enlighten  us  still  more  as  to 
the  part  played  by  the  cortex  in  the  functions  of  the  brain. 

B.  RejiovaIv  or  the  cortex  in  birds. — Removal  of  the  cortex  in  birds  (especi- 
ally in  the  pigeon)  has  been,  since  the  experiments  of  Flourens,  repeated  by 
Schrader  and  by  Mnnck,  who  limited  the  destruction  to  the  cortex  and  did  not 
injure  the  basal  ganglia.  According  to  Schrader,  and  Richet  held  the  same 
opinion,  the  results  obtained  by  Flourens  (motionless  position  and  loss  of  special 
sensations)  are  due  to  the  simultaneous  destruction  of  the  ojotic  thalamus  and  of 
the  cortex.  When  this  latter  alone  is  destroyed,  the  animal  can  still  see,  move, 
and  avoid  obstacles  ;  this  result  is,  however,  contested  by  Munck,  who  tliinks 
that  in  this  case  the  loss  of  vision  M^ould  be  quite  complete. 

Instinct  is  lost.  Movements  are  made  only  in  response  to  immediate  stimula- 
tions :  they  are  no  longer  spontaneous.  Differences  of  opinion,  as  noticed  above 
in  the  case  of  the  dog,  exist  chiefly  as  regards  the  persistence  of  sensations.  They 
seem  to  arise,  less  from  the  variation  in  the  results  of  exj^eriment,  than  from  the 
conceptions  formed  by  different  authors  as  to  what  is  to  be  imderstood  by  sensa- 
tion and  the  criteria  which  permit  of  its  recognition. 

C.  Removal  of  the  cortex  in  the  frog. — According  to  Renzi,  it  is  necessary, 
as  Longet  had  already  remarked,  to  distinguish  in  birds,  amphibians  and  reptiles 
a  mental  vision  requiring  the  integrity  of  the  cerebral  cortex,  and  a  crude  sensa- 
tion of  sight,  for  which  the  mesencephalon  is  sufficient.  According  to  Schrader, 
not  only  would  the  visual  sense  be  preserved,  but,  once  the  shock  of  the  operation 
over,  the  animal  would  be  able  to  change  its  place  and  its  sm-roundings,  accord- 
ing to  the  season,  and  to  find  its  own  nourishment  by  means  of  the  flies  Mhich 
it  catches.  The  instinct  of  the  animal  would  here  be  retained  as  well  as  sensation. 
Centralization,  which  is  well  defined  in  superior  animals,  and  which  has  placed 
the  nervous  system  in  dependence  on  the  brain,  has  so  far  made  but  little  progress 
in  batrachia. 

This  can  be  jjroved  by  dividing  the  spinal  cord  into  three  segments  by  two 
•sections,  one  of  these  represented  by  the  head,  the  second  by  the  superior  limbs, 
and  the  third  by  the  inferior  limbs,  each  having  an  independent  function. 

The  experiment  of  separating  tlie  encephalon  and  then  arousing,  by  stimula- 
tion of  the  skin  of  the  back,  the  reflex  action  of  the  spinal  cord,  is  well  known. 
The  movements  resLilting  from  this  stimulation  are  adapted  and  co-ordinated 
in  such  a  way  as  to  suggest  a  desire  for  the  removal  of  these  excitations  ;  they 
are,  in  their  own  fashion,  the  response  to  the  latter. 

3,  The  exchanges  between  the  brain  and  the  blood 

It  is  allowed,  in  principle,  that  the  activity  of  organs  is  connected 
with  an  exchange,  a  waste  (followed  by  a  recuperation)  of  these  organs. 
To  define  in  what  this  change  consists  is  the  problem  with  which  posi- 
tive science  is  confronted.  Only  as  regards  some  organs,  amongst 
which  the  muscle  may  be  particularly  mentioned,  has  the  solution  of 
this  problem  commenced.  The  methods  folloAved  and  the  results  ob- 
tained are  models  which  have  been  utilized  for  the  study  of  the  func- 
tions of  other  organs,  and  particularly  of  the  brain,  which  functions 
have  up  to  the  present  time  been  almost  incapable  of  explanation. 
This  method  is  a  legitimate  one,  provided  that  the  conclusions  arrived 


452  SYSTEMATIC    FUNCTIONS 

at  do  not  go  beyond  the  compass  of  the  facts.  By  experiments  copied 
from  those  which  have  served  to  define  the  function  of  muscle,  we  may 
attempt  to  clear  up  those  of  the  brain. 

Cycle  of  energy  in  the  muscle. — In  the  muscle,  the  leading  idea  of  these  experi- 
ments has  been  to  follow  through  it  a  double  cm-rent  of  matter  and  of  energy, 
which,  conveyed  from  the  exterior,  retvirns  there  after  having  formed  part  of  the 
muscle.  This  current  undergoes  in  it  a  kind  of  evolution,  in  which  three  principal 
phases  may  be  distinguished  (initial,  intermediate  and  final).  In  each  of  these 
matter  and  energy,  preserved  in  a  constant  c^uantity,  assume  characteristic 
forms,  which  answer  the  purpose  of  defining  muscular  function,  at  least  as  regards 
what  is  most  essential  to  it.  The  value  of  experiments  performed  on  the  muscle 
arises  from  the  fact  that  the  ascertained  results  are  not  only  qualitative,  but  also' 
quantitative,  and  that  the  quantitative  equivalence  of  the  successive  forms  of 
energy  guarantees  its  source  and  its  connexion.  In  the  muscle  matter  and 
energy  first  enter  the  muscle  and  then  leave  it  transformed  ;  they  enter  it  united 
and  leave  it  dissociated.  This  dissociation  of  matter  and  of  energy  may  even 
be  regarded  as  being  characteristic  of  the  muscular  function,  as  it  is  not  found 
in  the  same  degree  in  any  other  tissue.  In  the  muscle,  energy,  in  its  initial  or 
intermediate  phase  (at  the  time  of  its  entrance,  and  when  it  is  there  stored  up), 
is  present  in  a  chemical  form.  In  its  final  phase  (at  the  moment  of  its  leaving  the 
muscle)  it  is  partly  mechanical  and  partly  thei-mic.  The  function  of  muscle,  as 
it  appears  to  us,  is  essentially  an  energetic  function. 

The  very  simple  equation  of  the  combustion  of  the  blood's  glucose  in  the 
muscle  gives  us  information  concerning  both  these  mutations  of  matter  and  of 
the  liberation  of  energy  which  occurs  in  this  organ  at  the  moment  of  its  activity. 

Energetic  cycle  of  the  brain. — In  the  brain,  when  we  seek  to  establish  a  cycle 
of  the  same  nature,  we  find  several  elements  wanting.     It  may  be  that  these  are 
really  in  default,  or,  perhaps,  merely  that  experiment  has  so  far  been  found  incap- 
able of  revealing  them  to  us.     In  the  final  condition  of  this  cycle  there  manifestly 
can  be  no  mechanical  operation  ;    with  much  difficulty  it  has  been  possible  to- 
ascertain  in  certain  special  conditions  that  there  is  a  liberation  of  heat,  which  is. 
manifested  by  an  imperceptible  elevation  of  the  temperatm-e.      This  is  all  that  it 
is  j)ossible  to  grasp,  by  direct  means,  concerning  the  liberation  of  energy.     If 
we  wish,  as  in  the  muscle,  to  make  indirect  calorimetric  measurements,  that  is 
to  say,  to  ascend  to  the  source  of  energy  by  formulating  the  chemical  equation 
which  can   explain  its  production  to   us,  we   must   take    for  a    criterion    the 
oxygen   which    is   consumed  in  the  muscle,    and  the  carbonic  acid  which   is: 
produced  therein,  by  measuring  the  quantity  of  these  two  gases  in  the  blood 
which  enters  and  in  that  which  leaves  the  brain.     Experiments  of  this  nature 
have  been  performed  by  L.  Hill  and  D.  N.  Nabarro  ;  they  also  tend  to  prove  that 
the  cerebral  energetic  waste  of    tissue  is  a  very  slight  one.     The  table  which 
follows  shows  the  average  results  obtained  from  a  certain  niunber  of  experiments, 
giving  the  balance-sheet  of  the  gaseous  exchanges  in  the  brain,  and,  by  comparison, 
in  the  muscles  of  the  inferior  limb.     Experiments  have  been  made,  on  the  one 
hand  on  the  brain  and  the  nuiscles  in  a  state  of  repose,  or  at  least  after  their 
activity  had  been  diminished  by  morphia  narcosis  ;    and,  on  the  other  hand,  on 
the  brain  and  the  muscles  thrown  into  a  condition  of  hyper-activity  by  attacks 
of  epilepsy  provoked  by  means  of  an  injection  of  absinthe  or  of  strychnine.     The 
blood  was  taken  from  the  carotid  and  the  torcula  Herophili  in  order  to  estimate 
the  exchanges  in  the  brain  ;  from  the  carotid  and  the  deej)  femoral  vein  in  order 
to  form  an  estimation  of  the  changes  in  the  muscle  (arterial  blood  has  the  same 
composition  in  all  arteries). 


SUPERIOR  SYSTEIVIATIZATIONS 


453 


Comparison  of  the  gaseous  exchanges  in  the  brain  and  the  muscles  in  repose  and 

activity 


Gas  of 
the 
blood. 


C02   .. 


CO- 
02 


CO- 
02 


BRAIN. 


Carotid 
artery. 


48-85 
16-81 


44-98 
15-17 


30-59 
15-77 


Torcula 
Hero- 
phili. 


Differ- 
ence. 


MUSCLE. 


Carotid 
artery. 


Deep 
femoral 


Normal  state,  or  that  of  7'epose. 

44-74  +3-87  37-63      |   46-39 

13-39  -3-4  1810      I      5-12 

3-64  1 


49-04 
10-22 


33-58 
11-46 


Tonic  phase  of  epilepsy. 

j     +4-06      I    39-53        53-43 
-4-95      I     17-05  3-30 


4-50 

Clonic  phase  of  epilepsy. 

+  2-99      '     25-33         44-66 
-4-31  18-66  6-03 

3-65     ,  I 

Animal  under  morphia. 

45-75 
6-34 


C02 . . . 

37-6 

41-65 

+  401 

37-6 

02   ... 

18-25 

13-49 

-4-76 
;         4-38 

18-25 

Differ- 
ence. 


Reckoning  the 

co-efiic'ent  of 

circulation. 


8-76 
12-98 


10-84 


+  13-90 
-13-75 

13-82 


+  19-33 
-  12-63 


X  1=10-84 


x3=41-70 
X  3=  41-25 


x3=41-47 


X  3=  57-99 
X  3=  37-89 


15-98 


+   8-1 
-11-91 


X  3=  47-94 


10-00       =  10-00 


1.  Indirect  calorimetry. — Although  we  do  not  exactly  know  the 
nature  of  the  oxidative  process  which  makes  use  of  oxygen  in  the  brain 
and  produces  carbonic  acid  therein,  indirect  calorimetry  bears  witness, 
for  its  part,  to  the  small  waste  of  energy  in  this  organ.  However  small 
this  waste  may  be,  it  nevertheless  has  a  special  interest  if  we  can  only 
grasp  the  connexion  by  which  it  is  attached  to  another  aspect  of  the 
brain's  function,  namely,  to  the  jjsychical  phenomena  which  reveal  its 
internal  activity.  But  no  parallelism  between  these  two  orders  of 
phenomena  can  be  ascertained.  If  (as  it  has  been  possible  to  do  in 
the  case  of  loss  of  substance  of  the  skull)  a  sensitive  thermometer  is 
brought  into  contact  with  the  cerebral  cortex  of  a  human  being,  it 
will  not  be  found  that  the  temperature  is  lowered  during  sleep,  is  raised 
in  wakefulness,  or  is  exaggerated  during  the  most  intense  intellectual 
activity  ;  and,  if  oscillations  iwesent  themselves,  they  arise  ivithout  any 
necessary  agreement  with  the  variations  of  the  jjsychical  activity,  and 
sometimes  in  a  sense  opposed  to  that  which  has  just  been  indicated. 
It  has  been  possible  to  observe  them  during  deep  slumber.     Occasion- 


454  SYSTEMATIC    FUNCTIONS 

ally  they  have  appeared  to  coincide  with  unconscious  excitations  of 
the  senses  (external  noise,  but  not  sufficient  to  cause  awakening),  and 
reveal  rather  an  emotional  condition  than  an  act  of  comprehension, 
or  an  intellectual  effort.  In  animals,  elevation  of  the  cerebral  tempera- 
ture is  most  marked  when  asphyxia  is  produced,  and  attains  its  maxi- 
mum when  consciousness  has  vanished.  But  it  must  be  remarked 
that  the  thermometric  effect  is  only  obvious  a  certain  time  after  the 
cause  which  produced  it  has  ceased  to  act,  and  that  death  by  asphyxia 
is  preceded  by  a  certain  condition  of  over-excitement  of  the  whole 
nervous  system,  including  the  brain  (Mosso). 

The  elevation  of  temperature  thus  observed  is  correlative  with  the 
total  activity  of  the  cerebral  region  when  thermometrically  investigated ; 
the  phenomena  that  we  call  conscious  only  respond,  on  the  contrary, 
to  a  partial  activity  of  the  brain.  As  a  matter  of  fact,  in  the  brain, 
including  its  cortex,  unconscious  run  parallel  with  conscious  pheno- 
mena, and  it  is  impossible  to  separate  one  from  the  other,  because 
conscious  phenomena  are  alone  perceived  by  us  in  virtue  of  the  internal 
activity  of  the  brain.  Unconscious  phenomena  escape  us,  by  the 
same  definition.  Further,  the  field  of  consciousness  is  not  fixed,  but 
may  every  moment  become  larger,  or  smaller,  or  be  displaced  (in  wak- 
ing, in  sleep,  in  the  different  directions  in  which  attention  is  occupied). 
It  is  thus  obvious  that  no  co7mno7i  measure  between  heat  and  'psychical 
activity  can  exist  ;  or,  in  other  words,  between  heat  and  the  phenomena 
of  psychological  consciousness. 

2.  Heat  and  thought. — The  hope  has  been  entertained  of  finding,  by 
the  help  of  these  experiments,  an  equivalence  between  the  physical 
energy  which  our  external  senses  perceive  and  the  altogether  internal 
phenomenon  which  we  call  psychical,  precisely  because  it  is  perceptible 
to  our  internal  sense  alone.  Whatever  conception  may  be  formed  of 
one  or  the  other,  it  may  be  seen  that  the  problem  is  incapable  of  solu- 
tion by  experiment.  We  need  not  be  too  much  surprised  at  this. 
Amongst  physical  phenomena  heat  is  one  of  the  simplest  that  we  can 
discern  ;  on  the  contrary,  the  phenomenon  called  thought  is  one  of  the 
most  complex  we  are  capable  of  dealing  with  :  they  represent  to  us 
two  opposite  poles  of  phenomenality.  It  would  not  be  possible  for 
them  to  have  a  common  measure. 

3.  Cerebral  circulation. — The  cerebral  circulation,  considered  from  a 
purely  mechanical  point  of  view,  has  been  studied  elsewhere  (see  Cir- 
culation,  page  255)  ;  here  we  have  to  consider  it  in  relation  to  the 
cerebral  function  itself. 

The  relations  of  mutual  dependence  existing  between  the  heart  and 
the  brain  are  of  a  very  obvious  nature.     They  declare  themselves  in  a 


SUPERIOR  SYSTEMATIZATIONS  455 

striking  manner  whenever  one  of  these  organs  is  disturbed,  in  the 
performance  of  its  functions,  by  the  reaction  of  this  disturbance  on 
the  other. 

a.  Action  of  the  heart  on  the  brain. — A  momentary  stoppage  of  the 
heart  has  an  immediate  effect  on  the  cerebral  function,  displayed  by 
loss  of  consciousness  (commonly  called  loss  of  the  senses),  insensibility, 
muscular  flaccidity  ;  to  these  phenomena,  taken  as  a  whole,  the  name 
of  syncope  has  been  given.  No  organ  preserves  its  excitability  when 
deprived  of  its  blood  supply  ;  but  while,  as  regards  many  organs,  this 
loss  of  function  is  slow  and  gradual,  requiring  even  hours  for  its  full 
development,  we  see  that  in  the  case  of  the  brain  as  regards  its  grey 
matter,  and  especially  its  cortex,  this  loss  is,  so  to  speak,  instan- 
taneous in  warm-blooded  animals.  Experiment  confirms  this  fact  of 
every-day  observation.  Chauveau,  while  operating  on  the  cranial 
nerves,  noticed  that  sensation  did  not  outlive  the  last  beats  of  the 
heart.  On  the  other  hand,  the  excitability  of  the  motor  nerves  is  pre- 
served for  a  certain  time  after  death.  Motor  excitability  is  a  cellular 
function.  Sensation,  in  its  conscious  form,  is  a  function  appertaining 
to  a  complex  systematization  (brought  into  being  principally  in  the 
brain).  In  the  work  of  destruction  which  inevitably  follows  ansemia 
when  pushed  to  its  extreme  limits,  it  is  therefore  the  cellular  elements 
Avhich  are  primarily  separated  the  one  from  the  other  ;  ultimately 
disorganization  invades  these  elements  themselves,  following  a  regular 
order. 

b.  Action  of  the  brain  on  the  heart. — The  disturbances  of  brainfunction 
exert,  on  their  side,  a  reactional  influence  on  the  functions  of  the  heart. 
The  influence  of  emotions  or  of  different  passions  on  the  cardiac  rhythm 
is  well  known.  In  some  cases  this  rhythm  is  hastened  ;  in  others  it  is 
slackened  ;  sometimes  the  psychical  impression,  if  very  keen,  may  stop 
the  heart's  action  and  the  resulting  cerebral  anaemia,  as  well  as  the  loss 
of  consciousness,  wiirbe  found  to  be  the  consequence  of  an  impression 
which,  from  the  brain,  has  reached  the  heart,  and  then  secondarily 
affected  the  brain. 

By  their  exaggeration,  these  effects  are  suitable  for  symbolizing  the 
relations  existing  between  the  circulatory  system  and  the  nervous 
system,  of  which  the  heart  on  the  one  hand  and  the  brain  on  the  other 
represent  the  most  differentiated  parts.  The  action  of  the  brain  on 
the  circulation  is  not  in  fact  a  direct  one,  but  is  executed  by  the  inter- 
mediation of  an  order,  or  even  a  particular  system  of  nerves,  the  vaso- 
motor nerves.  Further,  this  action  is  not  limited  to  the  heart,  but  is 
propagated  to  the  arteries,  which  have  a  special  and  distinct  innervation 
almost  independent  of  that  of  the  heart. 


456  SYSTEMATIC    FUNCTIONS 

By  their  contraction,  the  arteries  of  the  brain  regulate  the  quantity 
of  blood  which  passes  through  this  organ,  and  this  contraction  is  in  its 
turn  governed  by  nerves  emanating  from  centres  subjacent  to  the 
brain,  which  adapt  its  impressions  to  the  regulation  of  its  own  circula- 
tion. 

4.  Vaso-motor  nerves  of  the  brain. — The  vaso-motor  nerves  of  the 
brain  are  contained  (at  least  partially)  in  the  cervical  cord  of  the  great 
sympathetic,  and  arise,  as  do  those  of  the  face,  from  the  superior  half 
of  the  thoracic  region  of  the  spinal  cord.  It  is  by  this  roundabout 
route  that  an  impulse  emanating  from  the  brain,  and  destined  for  its 
own  vessels,  reaches  the  latter.  In  the  brain,  as  in  other  organs,  the 
circulation  (delivery  of  blood)  is  proportionate  to  the  activity  of  the 
function.  Regulative  mechanisms  are  provided  to  ensure  this  pro- 
portionahty.  These  are  formed  by  reflex  cycles,  whose  centres  of 
reflexion  are  found  in  other  places  than  the  brain  itself,  in  the  medulla 
oblongata,  or  in  the  spinal  cord. 

The  arteries  of  the  brain  are  in  no  sense  independent  of  the  action  of 
the  vaso-motor  system,  though  some  have  declared  the  contrary  to  be 
the  case.  Their  muscular  elements  receive  nervous  plexiform  threads, 
anatomically  (Bourgery)  and  histologically  (Obersteiner)  demonstrable. 
The  very  first  experiments  performed  on  the  cervical  sympathetic 
demonstrated  the  fact  that  section  and  stimulation  of  this  nervous 
cord  reverberate  on  the  circulation  of  the  brain. 

The  application  of  vaso-myograj^hic  methods  to  this  circulation  has 
again  demonstrated  to  E.  Cavazzani  the  reality  of  this  influence.  Accord- 
ing to  this  author,  the  cervical  sympathetic  contains  vaso-constrictor  and 
vaso-dilator  elements  for  the  brain  (as  well  as  for  the  face  and  the  retina). 
The  first  react  most  powerfully  to  electrical  stimulation,  their  excita- 
bility is  soon  extinguished.  The  second  react  still  more  vigorously 
under  the  influence  of  ansemia. 

Stimulation  of  the  cervical  sympathetic  in  man. — Jonesco  and 
Floresco  have  stimulated  the  cervical  sympathetic  in  man  under  cir- 
cumstances permitting  the  estimation  of  the  cerebral  circulation.  Its 
diminution  is  produced  by  feeble  stimuli,  leading  to  a  contraction  of 
the  vessels  ;  its  augmentation  by  strong  stimuli,  tending  to  their  dila- 
tation. This  is  a  proof  of  the  existence  in  the  cervical  sympathetic  of 
elements,  the  one  constrictor  and  the  other  dilator,  destined  for  the 
brain  precisely  as  they  exist  in  it  for  other  organs. 

Hypophysis. — ^The  hypophysis  cerebri,  or  pituitary  gland,  is  an  organ  whose 
functions,  though  still  very  obscvu-e,  resemble  those  of  the  thyroid  and  para- 
thyroid glands,  these  having  general  nutrition  and  also  that  of  the  nervous  system 


SUPERIOR  SYSTEMATIZATIONS 


457 


itself  under  their  control.  These  functions  will  be  examined  in  their  appropriate 
place  among  the  secretions.  The  anatomical  connexion  of  this  organ,  of  which 
the  larger  part  is  glandvdar,  with  the  brain  is  exjalained  by  comparative  anatomy. 
In  the  Amnocetus,  the  neural  cavity  (which  represents  the  ependymal  canal 
with  its  ventricles)  communicates  with  the  mouth  by  a  bucco-ventricular  canal, 
and,  at  its  other  extremity,  with  the  intestine  by  a  neuroenteric  canal.  A  circula- 
tion of  water  is  maintained  in  this  aquiferous  system,  thanks  to  the  movements 
of  the  vibratile  cilia  of  its  wall  at  the  entrance.  Around  the  bucco-ventricular 
canal  is  the  jaituitary  body,  formed  of  epithelial  cells  of  epiblastic  origin  and  also 
of  nervous  elements  constituting  a  sort  of  centre  or  special  system.  The  aqui- 
ferous circulation  which  goes  on  in  the  nein^al  canal  ensm-es  the  nutrition  and  the 
oxygenation  of  the  nervous  system  in  these  animals  deprived  of  blood-circulatory . 
apparatus.  The  secretory  product  cast  out  by  the  pituitary  at  the  entrance  of 
this  cm'rent  is  carried  away  by  it,  reabsorbed,  and  thus  fulfils  its  imknown 
function. 


Haben'ila      Optic,  thai. 


Trijon 


Pineal  gl 


Splenium 


Ant.  corpus  quad. 


Pig.   200. — Hypophysis  (pituitary  gland)  and  epiphysis  (pineal  gland)  (after  Charpy)- 

When,  in  the  coiu'se  of  phylogenetic  development,  the  vessels  make  their 
ai^pearance  it  is  the  bloed  which  distributes  both  the  oxygen  and  the  secretory 
product  ;  the  canal  is  then  closed  and  the  ventricles  are  shut.  The  thyroids 
are  also  glands  annexed  to  the  respiratorj^  apparatus,  and  their  method  of  acting 
on  assimilation  seems  to  resemble  that  of  the  pituitary  body. 

Epiphysis. — The  epiphysis  cerebri,  or  pineal  body,  is  also  an  organ  on  the  retro- 
grade path.  It  is  considered  to  have  once  belonged  to  the  sense  of  sight.  In 
phj'logenetic  development  it  represents,  in  certain  inferior  vertebrates,  a  single 
median  eye,  which  opened  outside  by  the  parietal  orifice,  still  existing,  especially 
in  the  Saurians.  The  new  and  indeed  very  much  less  important  functions  of  the 
epiphysis  in  superior  vertebrates  are  practically  unknown  ;  they  are  nevertheless 
■classed  with  those  which  ensure  the  nutrition  of  the  nervous  system. 


D.     CEREBRAL  LOCALIZATION 
Flourens  has  submitted  the  nervous  system  to  an  analysis  which  has 
-enabled  him  to  distinguish  the  different  functions  of  its  most  obvious 


458  SYSTEMATIC    FUNCTIONS 

segments.  According  to  him,  execution  of  movements  appertains  to 
the  spinal  cord,  their  co-ordination  to  the  cerebellum,  their  voluntary 
initiation  to  the  brain  :  this  is  the  first  localization  of  the  functions  of 
this  great  system.  His  methods,  very  correct  fundamentally,  but 
insufficient  in  detail,  led  him  to  regard  the  brain,  on  the  contrary,  as  a 
homogeneous  mass  refractory  to  analysis.  New  methods,  more  appro- 
priate to  the  end  in  view,  have  in  their  turn  dissociated  the  internal 
parts  of  this  organ,  as  the  preceding  ones  had  separated  it  from  specifi- 
cally different  homologous  systems.  This  logical  march  of  analysis 
was  necessary  in  order  that  it  might  bear  fruit.  Its  slowness  is  suffi- 
ciently explained  by  the  difficulties  of  all  kinds  inherent  in  the  subject, 
by  the  various  questions  to  which  it  gives  rise,  and  by  the  opposition 
with  which  all  newly  ascertained  facts,  with  which  the  mind  has  not 
had  time  to  familiarize  itself,  are  at  first  met. 

The  method  of  Flourens  consisted  essentially  in  the  systematic 
removal  of  parts  whose  functions  he  wished  to  determine.  The  method 
of  stimulation  was  not  unknown  to  him,  but  it  was  at  that  time  prac- 
tised in  a  rough  manner,  as,  for  instance,  by  plunging  a  stylet  into  the 
brain  through  the  skull.  Electrical  stimulation  under  the  ordinary 
form  of  alternating  induced  currents,  is  of  recent  employment  ;  and 
for  nervous  structures,  such  as  the  brain,  it  is  the  only  efficacious 
method.  The  continuous  current,  very  inferior  to  the  preceding  one^ 
can  nevertheless  be  employed  to  produce  this  stimulation. 

I.  Localization  in  consciousness 

As  might  have  been  predicted,  it  is  in  the  conscious  life  that  the 
first  phenomena  furnishing  evidence  of  functional  localizations  in  the 
brain  have  been  recognized. 

1.  Initial  fact. — ^Hitzig,  having  noticed  that  in  man  galvanic  cur- 
rents applied  to  the  posterior  region  of  the  head,  or  to  the  temporal 
region,  produced  movements  of  the  eyes,  made  use  of  this  method  in 
order  to  study  methodically  with  Fritsch  the  effects  of  stimulation  of 
the  cerebral  cortex  in  animals,  and  particularly  in  the  dog.  These 
authors  have  found  that  a  portion  of  the  hraiii's  cortex  is  7notor  (which 
is  usually  interpreted  by  saying  that  it  is  excitable),  ivhile  the  other  parts 
are  not  ynotor.  To  put  it  otherwise,  stimulation  of  a  portion  of  the 
convexity  of  the  brain  gives  rise  to  movements  of  different  parts  of  the 
body,  movements  whose  nature  and  genesis  are  disputable,  but  which 
are  no  longer  produced  when  the  position  of  the  exciting  agent  is  shifted 
to  the  outside  of  a  fairly  well  defined  area  of  which  the  position  and 
limits  are,  apart  from  certain  variations,  constant.  These  movements 
take  place  in  the  part  of  the  body  opposite  the  stimulation  :   they  are 


SUPERIOR  SYSTEMATIZATIONS  459 

crossed,  and  are  also  localized  in  some  determinate  region,  as  the  upper 
or  lower  limb,  or  the  eyes,  varying  according  to  the  point  stimulated 
in  the  cortex.  The  area  called  motor  is  thus  itself  subdivisible  into 
smaller,  partial  areas.  These  movements  are  combined  muscular 
contractions,  producing  a  change  of  position  in  a  definite  direction  ; 
they  have  an  inteyitional  character.  According  to  the  point  stimulated 
in  the  area  corresponding  to  a  limb,  the  movements  of  this  limb  will 
be  either  those  of  flexion,  extension,  or  some  other  regular  alteration 
of  position. 

These  facts  were  confirmed  by  Terrier  in  England  and  Carville  and 
Duret  in  France,  in  the  case  of  the  donkey,  the  monkey,  the  dog,  and 
different  animals ;  Arloing  studied  them  in  the  solipedia  ;  Frangois- 
Franck  and  Pitres  made  on  this  subject  a  very  circumstantial  and  critical 
investigation.  Luciani,  Sepelli  and  Tamburini  in  Italy  also  gave  them 
a  new  extension.  As  regards  the  essential  facts,  they  were  agreed  ; 
discord  commenced  when  the  question  of  their  interpretation  arose. 

Method  of  stimulation. — Excitation  is  effected  by  means  of  alternating  induced 
currents  with  a  rhj'^thni  of  about  ten  to  the  second.  Stimulation  brought  to  bear 
on  ganglionic  organs  like  the  brain  (or  on  the  nerves  which  proceed  to  it)  has 
effects  in  every  way  different  from  those  obtained  by  directlj'  stimulating  the 
motor  nerves.  In  these  latter  the  response  follows  faithfully  each  elementary 
stimulation,  and  assumes  the  rhythm  of  the  component  stimulus.  In  the  first- 
named,  excitation  only  acts  effectually  when  it  is  repeated,  that  is  to  say  renewed. 
Further,  the  response  no  longer  copies  the  excitation,  but  takes  a  laarticular  form, 
which  depends  on  the  organization  of  the  nervous  complexus  stimulated.  The 
brain,  in  order  to  give  rise  to  the  same  motor  response,  can  therefore  accommodate 
itself  to  a  sufficiently  varied  range  of  rhythms.  Nevertheless,  the  rhythm  of  the 
excitation  is  never  quite  indifferent  to  it.  According  to  Richet  and  Broca,  the 
stimulating  effect  of  each  induction  shock  should  be  followed  (as  in  the  heart's 
ganglia),  bj'  a  refractory  pJiase,  which  diminishes  the  useful  effect  of  the  following- 
shock,  should  it  arrive  before  the  end  of  this  jaliase.  For  the  excitation  of  a  brain 
in  a  determined  condition,  there  must  therefore  be  an  optimum  rhythm  which 
should  be  sought  for.  This  rhythm  may  vary  according  to  the  individual 
(de  Varigny). 

Mechanical  stimvili  are  usvially  inefficacious,  except  when  the  cerebral  excit- 
ability is  augmented  by  a  slight  degree  of  inflammation. 

2.  Discord  in  the  interpretation. — This  discord  may  be  explained  by 
the  very  novelty  of  the  facts  to  which  the  attention  was  directed.  The 
tendency  (after  all  a  natural  one)  was,  as  is  usual  in  such  cases,  to  con- 
nect them  with  facts  already  known.  The  movements  initiated  by 
excitation  in  animals  are  of  two  kinds  ;  they  arise,  to  put  it  more 
clearly,  under  two  very  different,  and  in  certain  respects  opposite, 
circumstances.  The  first  are  produced  by  stimulations  directed  to 
the  muscles,  or  to  the  terminal  portions  of  the  nervous  system,  which 
end  in  the  muscles  ;   these  have  a  purely  physical  aspect.     The  second 


460  SYSTEMATIC    FUNCTIONS 

are  produced  by  excitations  brought  to  bear  on  the  organs  of  the  senses, 
or  on  the  initial  portions  of  the  nervous  system,  which  are  connected 
with  them  ;  they  give  rise  to  sensory  phenomena,  of  which  these  move- 
ments are  obviously  the  interpretation  ;  they  bear  witness  to  the 
existence  of  a  psychical  fact.  The  intermediate  portion,  the  brain,  the 
cortex,  was  considered  incapable  of  excitation  ;  consequently  the 
question  to  be  solved  was  not  as  to  which  of  the  two  preceding  classes 
the  movements  which  might  arise  from  its  being  placed  in  a  condition 
of  direct  activity  belonged.  Rather  the  novelty  consisted  in  the  fact 
that  the  excitation  of  this  part  should  produce  movements  at  all. 

For  their  better  characterization  an  effort  has  been  made  (by  some 
at  least)  to  identify  them  with  one  or  the  other  of  the  two  known 
categories.  For  some  they  were  the  revelation  of  a  purely  motor 
phenomenon,  as  if  the  stimulus  in  its  propagation  to  the  muscles 
traversed  a  homogeneous  area,  having  its  origin  in  the  cerebral  cortex 
(Ferrier).  For  others,  they  possessed  the  character  of  a  purely  sensory 
phenomenon,  as  if  the  direct  excitation  of  the  cortex  only  repro- 
duced, under  a  new  form,  the  indirect  excitation  that  the  centripetal 
nerves  carried  to  it  from  the  skin,  across  a  homogeneous  sensory  field. 
This  excitation  would  be  equally  reflected  in  some  special  motor 
centre  situated  lower  down  (Schiff). 

The  original  interpretation  given  by  Fritsch  and  Hitzig  was,  it  must 
be  confessed,  less  exclusive.  The  excitable  areas  whose  existence 
they  had  discovered  on  the  surface  of  the  brain,  and  which  they  called 
centres,  were  denominated  by  them  psycho-motor  centres.  Motor,  they 
certainly  were,  since  movement  resulted  from  their  stimulation  ;  in 
their  eyes  they  were  psychical  also,  because  these  movements  possessed 
that  character  of  association,  combination,  and  adaptation  by  means 
of  which  we  recognize  the  psychical  nature  of  a  motor  manifestation. 
To  make  their  conception  more  precise,  they  maintained  that  it  is  in 
these  centres  that  the  faculty  of  representation  of  the  movements  of 
correspomling  limbs  resides  ;  this  representation  having  its  source  in 
the  indications  of  the  muscular  sense  given  by  the  nerves  which,  from 
the  muscles,  ascend  to  the  brain,  and  no  doubt  end  in  these  centres. 
It  is  therefore  in  an  association  of  sensibility  and  motricity  that  these 
authors  have  at  first  sought  the  explanation  of  the  facts  discovered 
by  them,  an  association  limited  to  a  certain  modality  of  sensation  and 
of  movement,  but  which  ulterior  observations  and  experiments  will 
tend  to  extend  to  the  tactile  sense  in  its  entirety. 

3.  Number  and  situation  of  the  areas  capable  of  excitation. — Fritsch 
and  Hitzig  (1870),  in  their  experiments  on  the  dog,  have  recognized  a 
centre  for  the  muscles  of  the  neck  ;    a  centre  for  the  extensors  and 


SUPERIOR  SYSTEMATIZATIONS 


461 


adductors  of  the  anterior  limb  ;  further,  centres  for  the  flexion  and 
rotation  of  this  hmb  ;  a  centre  for  movements  of  the  j)osUrior  limb, 
and  one  for  those  of  the  face. 

a.  Dog. — According  to  these  authors,  the  centre  of  the  muscles  of  the  neck(  A ) 
is  situated  in  the  lateral  portion  of  the  pre-frontal  gyrus,  at  the  j)oint  where  this 
convolution  abruptly  descends.  The  centre  for  the  extensors  and  adductors  of 
the  anterior  limb  (  +  )  is  at  the  external  extremity  of  the  post-frontal  gj-rus,  in 
the  neighbourhood  of  the  lateral  extremity  of  the  frontal  fissure.  A  little  behind 
this  same  fissure,  and  nearer  to  the  coronal  fissure,  are  tlie  centres  for  the  flexion 
and  the  rotation  of  this  limb  (  +  ).  The  centre  for  the  posterior  limb  (  ::  )  is  also 
found  in  the  post-frontal  gyrus,  but  nearer  to  the  median  line  than  is  that  of  the 
anterior  limb,  and  a  little  farther  back.  The  centre  for  the  facial  muscles  (  ;;  ) 
is  in  the  middle  portion  of  the  super-sylvian  gyrus. 

The  results  betray  some  inconsistency  in  all  that  concerns  the  movements  of 
the  neck,  and,  fvu-ther,  contractions  of  the  back,  of  the  tail,  of  the  abdomen  of  an 
inconstant  nature  were  obtained  by  stimulating  the  regions  intermediate  to  those 
mentioned  above,  but  these  movements  did  not  j^resent  the  same  fixity  as  the 
preceding  ones.  On  the  other  hand,  the  whole  of  the  convexity  situated  behind 
the  facial  centre  appeared  to  these  authors  to  be  quite  irresponsive  to  excitation, 
even  when  much  stronger  currents  were  made  use  of.  (Hitzig,  Untersuchimgen 
iiber  das  Gehirn,  Berlin,  1874.) 

Extension  of  the  excitable  area. — Ferrier,  when  recommencing  his 
experiments  on  locahzed  stimulation  of  the 
cerebral  cortex,  repeated  them  on  the  dog, 
and  at  the  same  time  on  other  carnivora, 
and  on  animals  situated  either  higher  or 
lower  in  the  series  (monkey,  cat,  guinea-pig, 
rat,  pigeon,  frog).  As  regards  the  dog,  he 
found  that  its  excitable  area  extends  pos- 
teriorly as  far  as  the  fissure  of  Sylvius,  with 
a  tendency  to  go  beyond  it.  The  number 
of  these  centres,  that  is  to  say  of  localities 
in  the  cortex  whose  excitation  provokes  co- 
ordinated movements  of  a  particular  kind,  is 
increased.  This  author  defines  the  areas  by 
numbers,  and  these  he  makes  to  correspond 
in  the  monkey  and  the  carnivora.  Some  of 
these  numbers  are  wanting  in  these  latter, 
when  compared  with  the  monkey,  whose 
brain  is  more  differentiated. 

Motor  centres  and  sensory  centres. — -Ferrier  does  not  regard  all  these 
centres  as  being  motor,  even  in  the  restricted  sense  wliich  Hitzig  attri- 
butes to  this  word.  The  simple  fact,  says  he,  that  movements  result 
from  the  stimulation  of  a  given  part  of  the  hemisphere  does  not  neces- 
sarily imply  that  this  part  is  a  motor  centre,  as  commonly  understood. 


Fig.  201.— Brain  of  the  dog, 
showing  the  psycho-motor 
centres  determined  by  the 
researches  of  Fritsch  and 
Hitzig. 

A,  movements  of  tlie  muscles 
of  the  neck  ;  + ,  extension  and 
adduction  of  the  fore  li  mb  ;  + , 
flexion  and  rotation  of  the  fore 
limb  (behind  the  preceding)  ; 
}  movements  of  the  posterior 
limb  ;  O,  movements  of  the  face. 


462  SYSTEMATIC    FUNCTIONS 

According  to  him,  there  are  certain  motor  responses  to  the  stimulation 
which  express  the  sensation,  and  the  character  of  these  movements 
would  thus  form  an  important  index  to  the  nature  of  the  sensation. 
Thus  Ave  find  that,  at  the  very  beginning  of  all  research,  the  question 
arises,  embarrassing  to  all  those  who  have  worked  on  this  subject  : 
namely,  by  what  characteristics  shall  we  recognize  motricity  and  by 
what  sensibility  ?  And  if  these  two  conditions  are  distinct,  where 
are  motricity  and  sensibility  situated  ? 

According  to  Terrier,  the  criterion  seems,  above  all,  to  lie  in  the  degree 
of  complication,  association,  and  co-ordination,  and  it  might  be  said 
of  purpose,  in  the  movements  provoked.  The  more  simple  movements 
would  indicate  motor  centres  ;  but  if  these  simple  movements  are  asso- 
ciated amongst  themselves,  as,  for  example,  the  movement  of  the  eyes 
and  of  the  head  in  the  same  direction,  and,  still  more,  that  of  the  head, 
the  eyes  and  the  ears  in  a  combined  attitude  expressive  of  attention, 
it  must  be  that  the  stimulus  has  brought  a  sensory  centre  into  play. 
The  complication  of  the  question  is  completed  by  the  fact  that  stimula- 
tion of  the  same  point  of  the  cortex,  according  to  the  persistence  of 
the  excitant,  or  the  actual  value  of  the  excitability,  may  produce  effects 
which  are  sometimes  simple  and  sometimes  complex.  The  movements 
of  the  axes  of  the  eyes  may  be  produced  alone,  or  may  be  accomi3anied 
or  followed  by  those  of  the  head  and  the  ears. 

Relative  characters. — As  a  matter  of  fact,  when  we  make  observa- 
tions outside  ourselves,  that  is  to  say,  external  to  our  own  proper  con- 
sciousness, sensation  and  motion  are  distinguished  the  one  from  the 
other  by  characters  which  are  not  absolute,  but  relative.  It  is  by 
relation  the  one  to  the  other  that  two  nervous  elements,  two  systems 
or  two  centres,  placed  in  succession,  are  the  one  motor  and  the  other 
sensory,  and  the  objective  difference  between  the  one  and  the  other 
(which  is  made  obvious  by  the  comparison  of  their  excitation)  is  never 
greater  than  when  the  excitation  is  directed  to  the  parts  between  which 
a  larger  number  of  neurons,  of  systems,  or  of  transforming  centres  are 
interposed  (example  :  comparative  excitation  of  the  posterior  and 
anterior  roots)  ;  and  this  difference  is  never  smaller  than  when  these 
parts  follow  each  other  in  immediate  succession  (example  :  the  cortex 
of  the  brain). 

Artificial  stimulation  and  normal  activity.^ — On  the  other  hand,  it 
must  not  be  forgotten,  that  the  manner  in  which  the  stimulus  is  made 
to  penetrate  the  nervous  system,  in  dealing  with  the  brain,  is,  taking 
it  altogether,  very  artificial,  and  does  not  necessarily  resemble  that 
which  arises  apparently  spontaneously  in  this  organ  in  the  course  of 
psychical  activity.     For  the  purpose  of  analysis  we  limit  the  stimula- 


SUPERIOR  SYSTEMATIZATIONS  463 

tion  to  a  point  of  the  cortex  as  circumscribed  as  possible,  and  this  is 
roused  into  a  state  of  activity  by  the  electric  current.  From  this  point 
the  stimulus  is  propagated  by  radiation,  assuredly  not  of  a  physical 
nature  (this  cause  of  error  may  be  eliminated  by  suitably  graduating 
the  intensity  of  the  current)  but  physiological,  that  is  to  say,  by  reaction 
of  the  excitation  by  means  of  the  elements  directly  excited  on  those 
in  regular  connexion  with  them.  That  which  results  most  clearly 
from  the  observation  of  these  effects  is  the  copiousness  and,  at  the  same 
time,  the  extent  of  these  connexions,  in  the  first  instance  in  the  brain 
itself,  afterwards  between  this  organ  and  its  subjacent  systems.  It  is 
also  the  pre-established  order  of  these  connexions  which  causes  the 
stimulation  of  determinate  points  to  be  manifested  by  motor  effects 
equally  determinate,  and  variable  according  to  these  points.  In  spite 
of  the  fact  that  we  cannot  avoid  certain  causes  of  error,  for  example, 
the  bringing  simultaneously  into  play  of  elements  of  which  some  may 
be  excitatory  and  others  inhibitory  ;  or  again,  elements,  some  of  projec- 
tion, others  of  association,  etc.,  this  method  is  especially  valuable  for 
the  analysis  which,  by  aid  of  it,  can  be  made  as  concerns  the  working 
of  the  brain  ;  in  the  sense  that,  when  we  observe  movements  normally 
produced  resembling  those  which  we  arouse  by  stimulation  of  a  point, 
or  of  a  limited  area,  of  the  cortex,  we  may  conclude  that  this  locality, 
or  this  area,  must,  in  a  certain  way,  participate  in  the  normal  execution 
of  these  movements,  and  also  in  the  psychic  processes  connected  at 
that  moment  with  the  execution  of  them. 

But  this  method,  which  is  favourable  to  analysis,  only  enlightens  us 
to  a  very  small  extent  concerning  the  phenomena  of  sensation,  which 
are  pre-eminently  of  a  synthetic  nature.  The  phenomena  of  cerebral 
activity  elicited  b}'-  stimulation  localized  at  a  given  point  of  the  cortex 
may  be  implicated  in  a  sensation  either  actual  or  remembered  (at  the 
present  moment,  or  in  memory),  but  nothing  proves  to  us  that  they 
form  the  totality  of  this  sensation.  Nothing  tends  to  prove  that  this 
sensation  or  this  memory,  when  they  are  the  starting  point  for  motor 
acts,  even  if  resembling  those  produced  by  the  localized  excitation  of 
the  cortex,  have  for  their  origin  a  state  of  activity  of  an  area  also 
restricted  to  this,  from  whence  the  others  are  invaded  by  it.  In  fact, 
we  know  that  the  actual  sensation  (the  one  arising  from  a  stimulation 
apphed  at  the  periphery  of  the  nervous  system)  requires  for  its  develop- 
ment a  certain  extent  of  the  sensory  area  and  of  the  cortex  ;  at  least 
this  seems  to  be  the  conclusion  to  be  drawn  from  the  dispersion  im- 
pressed upon  it  by  the  paths  it  is  obliged  to  follow  after  leaving  the 
spinal  cord.  In  any  case,  in  all  that  concerns  sensation,  it  is  necessary 
to  be  very  careful  in  the  interpretation  given  to  the  effects  of  stimulation 


464 


SYSTEMATIC    FUNCTIONS 


of  the  brain,  and  also  in  the  comparisons  we  may  be  tempted  to  dra-.v 
between  it  and  the  normal  processes  of  cerebral  activity.  This  much 
may  be  conceded  to  Ferrier,  that  the  more  a  motor  act  permits  of  asso- 
ciated systems,  so  much  the  greater  probability  is  there  of  its  being 
accompanied  by  a  psychism  of  an  exalted  nature,  and  also  perhaps  by 
a  conscious  sensation.  But  the  difference  is  not  absolute,  it  is  only  a 
question  of  degree. 

Now  tliat  these  reservations 
have  been  made,  we  may  de- 
scribe the  objective  effects 
(definite  movements)  which 
are  prodviced  in  response  to 
excitations  of  different  points 
of  the  cortex  according  to  the 
numbers  of  Ferrier.  These 
numbers  being  represented 
in  their  respective  positions 
on  a  plan  of  the  external  sur- 
face of  the  dog's  brain,  in 
order  to  ascertain  the  area  of 
each  it  is  only  necessary  to 
look  back  to  the  description 
of  the  convolutions  of  the 
brain  in  carnivora. 

(1)  The  opposite  hind  paw 
advanced  for  walking. 


JV 

Fig.  202. — Brain  of  the  dog  (left  hemisphere). 
Motor  or  sensori-motor  centres,  according  to  the 
nomenclature  of  D.  Ferrier. 

A,  fissure  of  Sylvius  ;  B,  crucial  furrow  ;  O,  olfactory 
bulb  ;  I,  IT,  III,  IV,  1st,  2nd,  ^-rcl,  4th  convolution  of 
Ferrier,  who  reckons  them  starting  from  the  interhemi- 
spherical  fissure  ;  1,  4,  6,  etc.,  numbers  of  the  excitable 
points  of  the  cortex,  whose  motor  effects  are  described  in 
the  text. 

(3)  Undulatory    or    lateral  movements  of  the  tail. 

(4)  Retraction  and  adduction  of  the  opposite  anterior  limb. 

(5)  Elevation  of  the  shotdder  and  forward  extension  of  the  opposite  anterior 
limb. 

(6)  Occasionally,  but  not  always,  flexion  of  the  paw  accompanying  movements 
(4)  and  (5). 

( 7 )  Simultaneous  action  of  the  orbicularis 
ocidi  and  of  the  zygomatic i  causing  the 
opposite  eye  to  close. 

(8)  Retraction  and  elevation  of  the  op- 
posite angle  of  the  mouth  with  j^artial 
opening  of  the  latter. 

(9)  The  mouth  is  opened  and  the  tongue 
moves. 

(10)  Retraction  of  the  angle  of  the 
mouth. 

(11)  Elevation  of  the  angle  of  the  mouth 
and  of  the  side  of  the  face  in  order  to  shut 
the  eye. 

(12)  Opening  of  the  eyes  with  dilatation 
of  the  pupils,  the  eyes,  and  afterwards  the 
head,  turning  to  the  opposite  side. 

(13)  The  eyes  are  turned  to  the  opposite 
side. 

(14)  The  opposite  ear  is  suddenly  raised  or  retracted. 

(15)  The  nostril  of  the  same  side  is  twisted. 


Fig.  203. 
hemisphere 


—Brain  of    the    cat   (left 
(after  Ferrier). 
A,  fissure  of  Sylvius  ;    B,  crucial  sul- 
cus ;    O,  cut  olfactoiy  tract ;  I,  II,    III, 
IV,  the  external  convolutions,  reckoned 
starting    from      the    interhemispherical 
fissure ,    1,  4,   5,  etc.,    numbers    of    the 
excitable  points  of  the  cortex,  each  cor- 
esponding  to  a  determinate  motor  effect, 
he  same  for   each  number  in  different 
animals. 


SUPERIOR  SYSTEMATIZATIONS 


465 


(16)  Sometimes  elevation  of  the  lip  and  dilatation  of  the  nostril  ;  but  perhaps 
stimulation  of  the  olfactory  tract,  which  would  produce  these  movements  by- 
reflex  action. 

b.  Babbit. — The  rabbit,  the  guinea-pig,  and  the  rat  are  lissencephalic  ;  this 
makes  the  mapping  out  of  excitable  points  a  difficult  task,  but  a  diagi-am  will 
inake  it  clear. 

(1)  The  opposite  jDosterior  limb  is  advanced  (when  it  is  jireviously  extended). 

(4)  Retraction  with  adduction  of  the  opposite  anterior  limb. 

(5)  Elevation  of  the  shoulder  and  extension  forward  of  the  anterior  limb. 

(7)  Retraction  and  elevation  of  the  angle  of  the  mouth. 

(8)  Closing  of  the  opjaosite  eye. 

(9)  Opening  of  the  mouth  with  movements  of  the  tongue. 

(13)  Usually,  forward  movement  of  the  opposite  eye,  and  sometimes  rotation 
of  the  head  from  the  opposite  side. 

(14)  Sudden  retraction  and  elevation  or  erection  of  the  opposite  ear. 

(15)  Torsion  or  closing  of  the  nostril. 

c.  Guinea  pig. 

(1)  The  hind  paw  is  advanced. 

(5)  The  front  paw  is  raised  as  for  walking,  then  it  is  rapidlj^  dra\^ai  back  and 
brought  near  the  trunk. 

(7)  Retraction  and  elevation  of  the  angle  of  the  mouth. 

(8)  Closing  of  the  eye  and  raising  of  the  cheek. 

(9)  Opening  of  the  mouth. 
(14)  The  opposite  ear  is  erected. 

d.  Rat. — The  results  are  very  similar  to  those  obtained  in  the  guinea-pig  and 
the  rabbit. 

e.  Pigeon. — The  only  constant  motor  reaction  obtained  by  stimulating  the 
brain  of  the  pigeon  (in  tlie  superior  parietal  region)  is  a  strong  contraction  of  the 
opposite  pupil,  associated  from  time  to  time  with  a  rotation  of  the  head  in  the 
opposite  direction.     Occasionally  these  two  effects  could  be  dissociated. 

f.  Frog. — Movements  were  noticed  in  the  limb  opposite  to  the  hemisphere 
stimulated  ;    except  their  crossed  action,  nothing  could  be  clearly  recognized. 

o 


Fig.  204. — On  the  left,  brain  of  guinea-pig  (left  hemisphere).  In  the  middle,  brain  of 
rat  (superior  surface).  On  the  right,  brain  of  rat  (right  hemisphere)  ;  O,  olfactory 
lobe. 

1,  the  hind  paw  is  advanced  ;  the  fore  paw  raised  ;  1,  retraction  and  elevation  of  the  angle 
of  the  mouth  (mastication)  ;  8,  closure  of  the  eye  and  elevation  of  the  cheek  ;  9,  opening  of  the 
mouth  ;    14,  the  opposite  ear  is  pricked  up  (after  Ferrier). 

g.  Fish. — The  irritation  of  one  hemisphere  caused  the  tail  to  beat  from  the 
opposite  side,  while  the  pectoral,  dorsal  and  anal  fins  were  agitated  ;  the  move- 
ments were  comjDlex  and  irregular. 


The  determination  of  the  excitable  points  of  the  cortex  has  been 
carried  out  in  great  detail  on  the  monkey,  not  only  by  Ferrier,  but  by 
many  physiologists  after  him,  especially  in  England.     The  results  will 


p. 


HH 


466 


SYSTEMATIC    FUNCTIONS 


be  brought  forward  with  respect  to  specific  innervations  when  the 
tactile  cortical  zone  is  discussed.  Their  interest  lies  chiefly  in  the 
comparison  which  may  be  made  with  those  furnished  by  the  anatomo- 
chnical  method,  and  even  with  the  stimulation  which  has  been  some- 
times brought  to  bear  on  the  human  cortex. 

4.  Localized  ablations. — The  localized  stimulation  of  the  psycho- 
motor areas  enables  these  at  once  to  be  easily  recognized.  Localized 
removal  of  these  areas  confirms  the  indications  given  by  stimulation, 
by  causing  pa7'alyses,  also  localized  and  of  a  special  order,  to  appear, 
these  being  the  counterpart  of  the  preceding  facts.  But  the  location  of 
the  centre?  is  not  sufficiently  fixed,  nor  are  their  boundaries  sufficiently 
distinct,  for  it  to  be  possible  (after  trephining  the  skull  and  laying  bare 
the  cortex)  to  find  them  to  a  certainty.  Were  it  not  for  the  indication 
yielded  hy  stimulation,  the  search  for  these  centres  would  be  so  un- 
certain and  laborious,  that  it  is  easy  to  understand  that  this  method, 
as  formerly  practised,  would  never  have  led  to  their  discovery.  But 
if,  the  location  of  a  centre  haviyig  been  ascertained  by  excitation,  the  cortex 
corresponding  to  it  be  removed,  paralytic  phenomena  ivill  make  their 
appearance  in  precisely  the  same  region  as  that  of  which  the  excitation 
of  the  centre  caused  the  movements. 

The  functional  deficiency  following  this  ablation  is  not  a  paralysis, 
if  by  this  word  is  understood  the  total  loss  of  movement  in  the  corre- 
sponding limb.  The  limb  is  not  deprived  of  all  movement,  but  it  is 
deprived  of  one  of  the  determining  conditions  which  engender  this 
movement  in  it.  It  has  retained  reflex  and  automatic  movements, 
even  a  part  of  its  instinctive  movements  ;  on  the  other  hand,  it  has 
lost  those  movements  which  are  called  voluntary,  and  especially  those 

which  a  more  or  less  long 
and  patient  education  had 
acquired  for  it.      The  ani- 
mal can  make    use   of  its 
limb  for  walking  or  jump- 
ing, but  it  will   no  longer 
be  able  to  use  it  for  hold- 
ing the  bone  it  wishes  to 
gnaw,  or  "  to  give  a  paw," 
as  it  has  been  taught  to  do 
at  the  word  of  command. 
5.   Disturbances  of  sensation. — The  disturbances  of  sensation  which 
follow  a  limited  destruction  of  the  cortex  are  no  less  characteristic 
than  those  of  movement.     All  sensation  has  not  vanished  from  the 
limb  which  we  describe  as  paralysed.     The  animal  reacts  to  stimuli 


Fig.  205. — On  the  left,  pigeon's  brain.  In  the 
middle,  frog's  brain.     On  the  right,  carp's  brain. 

A,  cerebral  hemispheres;  B,  optic  lobes;  C,  cere- 
bellum; X,  location  of  an  excitable  point  in  the 
pigeon's  brain  (after  Ferrier). 


SUPERIOR  SYSTEMATIZATIONS  467 

applied  to  the  skin  of  this  hmb,  but  it  is  a  kind  of  sensation  that  is  at 
first  sight  seriously  altered.  Sensation,  the  conscious  representation 
of  the  attitudes  of  the  hmbs,  is  lost.  The  animal  often  walks  on  the 
dorsal  surface  of  its  toes  without  appearing  conscious  of  doing  so.  In 
repose,  in  the  upright  position,  it  often  falls  on  the  side  of  the  limb 
attacked  by  these  disturbances  of  sensation  and  movement  ;  it  can,  it 
is  true,  get  up  again  by  itself.  When  lying  down,  it  endures  the  most 
uncomfortable  positions,  without  trying  to  alter  them. 

When,  in  the  cortex,  we  remove  that  which  is  called  the  "  centre  " 
appertaining  to  a  limb,  or  to  any  segment  of  the  body,  we  obviously 
destroy  an  association  between  sensation  and  movement.  The  data 
yielded  by  experiment  agree  on  this  point  with  those  furnished  by 
anatomy,  which  shows  us  the  sensory  and  motor  tracts  mutually  con- 
nected in  a  certain  manner  in  this  cortex. 

The  corresponding  limb  has  not  lost  all  power  of  movement,  for  it 
is  seen  that  it  can  execute  many  and  even  complicated  acts  ;  it  has 
not  entirely  lost  sensation,  inasmuch  as  it  reacts  to  painful  and  even 
tactile  impressions.  This  is  because  the  sensory  nerves  of  the  hmb 
form  other  connexions  wdth  its  motor  nerves,  either  in  certain  areas 
of  the  cortex  different  from  the  first,  or  especially  in  the  grey  subjacent 
masses,  and  each  of  these  associations  answers  to  some  special  function. 
Of  these  functions,  the  one  which  is  exerted  in  the  area  of  the  excitable 
zone  corresponding  to  a  given  limb  has  for  chief  object  the  solidariza- 
tionof  motion  and  sensation  in  this  limb,  for  the  performance  of  certain 
conscious-voluntary  acts. 

Nevertheless,  it  is  not  only  that  which  is  usually  called  the  muscular 
sense  which  is  in  this  case  disturbed  or  destroyed.  If,  as  Tonnini  has 
remarked,  the  alterations  of  this  sense  are  graver  and  persist  longer, 
yet  all  varieties  of  sensation  are  in  reality  involved.  The  special  tactile 
sense  is  itself  diminished,  and  the  contact  of  bodies  is  only  perceived 
after  a  considerable  interval,  this  delay  being  due  to  retardation  under- 
gone by  the  transmission  and  elaboration  of  the  sensation  (R.  Tripier). 
Sensibility  to  pain  is  also  diminished,  as  are  also  the  tactile  sense  and 
the  coenesthetic  sensations  (Verger). 

6.  Comparison  of  motor  and  sensory  disturbances. — Compared  with 
motor  disturbances,  those  of  sensation  are  more  diffused,  and  sometimes 
reach,  but  imperfectly,  areas  (a  limb  for  example)  other  than  those  in 
which  the  motor  paralysis  is  localized.  They  are,  on  the  other  hand, 
more  fugitive,  and  in  about  a  couple  of  weeks  begin  to  diminish  and 
then  soon  disappear.  In  the  order  of  sensation,  as  in  that  of  move- 
ment, but  especially  in  that  of  sensation,  these  disturbances  are  the 
more  recognizable  and  durable  according   to  whether  or  not  a  more 


468  SYSTEMATIC    FUNCTIONS 

differentiated  function  is  in  question.  More  marked  in  the  foot,  and, 
above  all,  in  the  hand,  than  in  other  regions,  they  are  so  also 
in  superior  species,  rather  than  in  the  inferior  animals  (Mott). 

7.  Evolution  of  this  question. — The  question  of  cerebral  localization 
has  been  brought  to  the  front  by  the  discovery  of  an  excitable  area 
on  the  surface  of  the  brain.  For  a  short  time  it  seemed  necessary  to 
copy  its  first  expression  from  that  which  portrays  the  functions  of  the 
nerve  roots  by  simultaneously  distinguishing  between  the  nerves  of 
sensation  and  those  of  movement  in  them.  But  facts  soon  showed 
that  one  of  the  most  essential  functions  of  the  brain  is,  on  the  contrary, 
to  solidarize  sensation  and  motion,  to  efface  between  them  those 
characteristics  which,  without  being  absolute,  make  them  appear 
so  different  when  we  examine  them  at  the  periphery  of  the  nervous 
system  ;  and  to  effect  the  transition,  though  in  the  main  unknown, 
which  leads  from  one  to  the  other. 

The  actual  formula  of  this  discovery  is  founded  on  a  distinction  of 
another  order.  Sensation  is  no  longer  separated  from  movement  ;  the 
different  modalities  of  sensation  are  separated  instead,  at  the  same  time 
attaching  to  each  of  them  the  equally  different  modalities  of  that  variety 
of  motion  which  is  the  most  nearly  related  to  them.  In  this  way  a 
certain  number  of  sjmcifically  different  systems  are  constituted,  each 
one  answering  to  the  exercise  of  one  of  our  senses.  On  the  other  hand, 
it  must  not  be  forgotten  that  these  systems  are  connected  the  one  with 
the  other,  and  are  also  capable  of  resolution  into  their  constituent 
elements,  and  that  by  this  double  means  they  may  produce  the  most 
different  combinations. 

8.  The  tactile  system. — The  area  knowTi  as  the  excitable  area  of  the 
brain  defines,  on  its  surface,  the  locality  occupied  by  general  sensation 
or  the  tactile  sense.  The  muscles  of  the  limbs,  of  the  face,  and  of  the 
trunk,  which  are  in  immediate  anatomical  and  functional  connexion 
with  the  skin,  this  being  the  receptive  organ  of  tactile  excitations,  are 
naturally  attached  to  it  by  reflex  arcs  whose  circuit  is  completed  in  the 
spinal  cord,  the  optic  thalamus  and  the  cerebral  cortex.  Thus  arises 
a  natural  system  of  the  highest  importance,  namely  :  the  tactile 
system,  which,  answering  to  a  modality  of  sensation  common  to  all 
our  organs,  extends  its  roots  to  the  immense  majority  amongst  them, 
reserving  at  the  periphery  some  very  restricted  areas,  for  the  recep- 
tion of  stimuli  corresponding  to  the  other  senses. 

Alongside  this  system  are  placed  others,  constructed  on  the  same 
tjrpe,  but  at  the  same  time  specifically  different  both  as  regards  the 
nature  of  the  stimuli  which  bring  them  into  play,  the  sensations  arising 
within  and  the  movements  directly  at  the  service  of  these  sensations. 


SUPERIOR  SYSTEMATIZATIONS  469 

These  systems  are  represented  in  the  cerebral  cortex,  of  which  they 
occupy  certain  areas,  areas  whose  outhnes,  it  is  true,  are  not  very 
clearly  defined,  but  which  are  nevertheless  perfectly  distinct,  and 
whose  extent  cannot  be  measured  by  that  of  their  peripheral  area 
alone,  but  rather  by  the  importance  of  the  information  furnished  by 
them  to  the  sensorium. 

The  delineation  of  these  areas  is  the  precise  problem  of  cerebral 
localization,  such  as  it  exists  at  the  present  moment.  The  methods 
made  use  of  for  resolving  the  question  are,  on  the  other  hand,  those 
which  have  served  for  the  cortical  area  subserving  general  sensation. 
They  consist  of  locaUzed  and  methodical  destructions  of  the  cortex 
and  of  its  stimulation.  These  localized  destructions  are  followed  by 
sensorial  paralyses  of  a  nature  specifically  different,  according  to  the 
function  of  the  area  destroyed.  As  to  the  excitations,  they  produce 
movements  which  are  in  functional  relation  to  the  stimulated  area. 
Clinical  experience  has  also  furnished  a  valuable  quota  of  observations. 
9.  The  sensorial  systems. — By  means  of  information  drawn  from 
these  different  sources,  it  may  be  concluded  that  the  brain  is  composed 
of  different  parts,  of  differentiated  systematizations,  whose  principal 
modalities  correspond  with  the  five  different  senses  into  which  our 
sensibihty  is  divided.  The  posterior  part  of  the  brain,  its  occipital 
pole,  is  devoted  to  vision.  A  part  of  the  temporal  region  (first  and 
second  temporal  convolutions)  is  given  over  to  hearing.  The  limbic 
convolution  (the  whole  of  it  in  osmatics,  the  hippocampal  lobe  in  micros- 
matics)  is  appropriated  to  olfaction.  The  seat  of  taste  is  less  certain, 
but  is  probably  situated  in  the  neighbourhood  of  the  preceding  area, 
if  not  included  in  it. 

By  the  localized  destruction  of  one  of  these  areas  of  the  cortex  to 
the  exclusion  of  the  others,  an  individual  may  therefore  be  deprived 
of  a  determinate  order  of  sensations,  while  retaining  the  remainder. 
For  example  :  sensibility  to  light  may  disappear  (psychical  blindness) 
while  the  other  modes  of  sensibility  (tactile,  auditory,  etc.)  are  pre- 
served. It  seems  as  if  plain  facts  like  these  can  allow  of  no  further 
hesitation  as  regards  the  still  disputed  question  of  cerebral  localization. 

Localization,  differentiation.  —In  truth,  these  controversies  concern  less  the 
reality  of  the  facts  than  the  smtability  of  the  expressions  employed.  The  words 
"  centres  "  and  "  localizations  "  in  particular,  if  taken  literally,  can  only  serve 
to  perpetuate  these  discussions.  An  injury  localized  in  a  given  area  of  the  brain 
(or  of  the  nervous  system)  produces  a  definite  perturbation  of  the  fvinctions  of 
the  brain  (or  of  the  nervous  system)  ;  this  is  brought  out  clearly  from  the  facts 
of  observation  and  experiment,  and  definitely  imdermines  the  former  hypothesis 
of  the  homogeneity  of  the  brain's  functions.  Bvit  if  it  be  argued  from  this  that 
the  vanished  function  is  localized  in  the  area  of  the  brain  which  has  been  destroyed, 
the  conclusion  transgresses  the  limits  of  fact,  as  it  is  clear  that  the  function  whose 


470  SYSTEMATIC    FUNCTIONS 

disappearance  is  under  observation  requires  the  co-operation,  not  only  of  an 
area  of  the  cortex,  but  also  of  the  connecting  links  attaching  this  to  the  sub- 
jacent regions  of  the  nervous  system,  or  even  to  the  neigliboviring  regions  of  the 
cortex  itself.  And  if  it  is  said  that  this  function  is  centralized  here,  the  expres- 
sion is  not  much  more  accurate  ;  because,  in  spite  of  the  preponderating  part 
which  the  cortex  plays  in  the  connexion  between  the  elementary  acts  co-operating 
in  this  function,  it  does  not  exclude  the  part  played  by  other  associations  which 
are  produced  outside  the  cortex  in  masses  of  the  grey  matter  ;  these  possessing 
the  same  structure  as  the  cortex,  but  in  a  simplified  condition.  In  the  present 
state  of  our  knowledge  it  would  be  more  correct  to  say  that  the  brain  (like  the 
whole  of  the  nervous  system)  is  composed  of  differentiated  systems.  These 
systems  are  constructed  on  a  uniform  type  (cyclic  systems),  and  can  be  brovight 
into  action  only  by  the  agreement  of  their  component  parts  ;  but,  being 
repeated  either  in  a  parallel  or  successive  manner,  they  adapt  themselves  to 
different  functions  which  answer  either  to  a  variety  of  modalities,  or  to  the  elabor- 
ation of  their  primordial  function. 

In  one  direction  as  in  another,  this  differentiation  is  not  uneven  but  progressive. 
The  most  correct  formula  would  therefore  be  the  one  which,  while  insisting  on 
this  differentiation,  would  at  the  same  time  take  into  account  its  transitions  and 
its  gradations. 

Opposition  of  the  points  of  view. — With  regard  to  the  cerebral  localizations, 
Goltz  and  Munck,  while  fundamentally  insisting  on  the  same  facts  generally 
held  as  correct,  have  supported  two  almost  antagonistic  points  of  view.  Goltz 
removed  the  cerebral  cortex  from  a  dog  (with  the  exception  of  certain  portions 
in  the  neighbourhood  of  the  optic  nerve  and  the  olfactory  lobe).  Wlien  the 
animal  had  recovered,  he  endeavoured  to  ascertain  in  what  the  functional  defi- 
ciency following  such  an  operation  consisted.  He  found  that  the  animal  had 
retained  some  sensations,  notably  that  it  covild  see,  liear  and  smell  ;  he  even 
recognized  in  it  some  lingering  traces  of  instinct.  Munck,  both  from  his  own 
experiments  and  from  the  criticism  to  which  he  subjected  the  observations  of 
Goltz,  could  see,  in  the  functional  manifestations  of  this  dog  deprived  of  the 
cerebral  cortex,  only  very  complicated  reflex  movements,  without  any  trace  of 
consciousness. 

Differences  of  the  criteria. — The  following  is  the  criterion  of  Goltz.  In  living 
beings  other  than  ourselves,  we  recognize  the  existence  of  conscious  jihenomena 
only  by  the  motor  manifestations  to  which  they  give  rise  ;  and  we  recognize 
these  only  on  the  condition  that  they  are  a  logical  answer  to  the  stimuli  applied 
by  us  to  these  beings.  If  an  animal  cries  out  when  it  is  hurt,  it  is  reasonable  to 
infer  that  it  feels.  If  it  closes  its  eyes  before  a  too  brilliant  light,  it  does  so 
because  it  sees.  If  it  takes  to  flight  or  stops  its  ears  in  the  neighbourhood  of  a 
violent  noise,  it  is  because  it  hears.  If,  when  placed  in  the  presence  of  its  food, 
it  eats,  this  shows  that  it  has  still  the  instinct  of  self-preservation.  If  it  were, 
however,  without  a  cerebral  cortex,  or  even  without  a  brain,  how  much  in  degree 
it  would  retain  of  all  this  remains  still  to  be  determined. 

The  criterion  of  Munck  is  quite  different.  This  author  lays  down  as  a  principle 
the  fact  that  there  is  nothing  in  common  between  the  movements  called  reflex 
and  those  which  have  for  starting  point  the  internal  phenomena  of  the  con- 
sciousness. It  is  known,  says  he,  that  an  animal  with  the  spinal  cord  cut  (but 
not  destroyed)  is  sometimes  capable  of  performing  complicated  reflex  move- 
ments in  response  to  stimuli  applied  to  it.  These  so-called  conscious  manifesta- 
tions of  Goltz's  decerebrated  dog  are  only  much  more  coinplicated  reflex  actions, 
which  may  be  compared  to  those  of  the  sjiinal  cord.  The  cerebral  cortex  is 
alone  the  seat  of  conscious  actions.  The  author  does  not  take  into  consideration 
that  it  is  possible  to  reverse  his  reasoning,  and  by  degrading  consciousness  in 


SUPERIOR  SYSTEMATIZATIONS  471 

exactly  the  same  degree  as  that  to  which  he  raises  reflex  action,  to  attribute  it 
to  the  spinal  cord.  Nevertheless,  of  the  two  points  of  view  this  would  be  the 
more  scientific  ;  it  has  the  law  of  continuity  on  its  side,  while  the  other,  arguing 
from  certain  incontestably  great  differences  between  cerebral  and  medullary 
manifestations,  places  them  in  what  may  be  considered  as  an  absolute  opi^osition. 
In  short,  it  is  necessary  to  distinguish  between  a  crud&  and  an  elaborated 
sensation.  The  first  is  located  in  the  sub-cortical  centres,  and  becomes  the 
second  by  attaining  perfection  in  the  cerebral  cortex.  This  doctrine  was  the 
one  adopted  by  Longet,  who  confirmed  it  by  observing  that  a  pigeon  whose 
brain  had  been  removed  could  still  follow  with  its  eyes  a  light  moved  abovit  in 
front  of  it.  On  the  other  hand,  we  may  also  admit  that,  in  the  animals  most 
elevated  in  the  series,  the  cortex  plays  a  predominating  part  ;  while  in  inferior 
vertebrata  it  leaves  a  larger  share  to  the  activity  of  the  inferior  centres.  Richet 
has  observed  that  if,  in  the  pigeon,  the  cortex  alone  is  removed  (instead  of  the 
whole  brain)  the  resulting  deficiency  aniounts  to  very  little.  Of  these  two  sensa- 
tions, the  one  of  a  crude  nature  and  the  other  elaborated,  the  first  bj^  its  veiy 
imperfection  eludes  consciovisness  ;  it  is  only  made  known  to  us  by  becoming 
the  second,  that  is  to  say,  an  elaborated  sensation,  and  in  this  case  merely  plays 
the  part  of  an  indissociable  element.  It  is  therefore  necessarily  unknown  to  us 
except  by  reasoning. 

2.  Localizations  in  unconsciousness 
The  motor  effect  of  stimulation  of  the  cerebral  cortex  is  not  limited 
to  the  contractions  of  the  muscles  of  the  skeleton.  This  stimulation 
reacts  equally  on  the  movements  of  the  circulatioii  (heart  and  vessels), 
on  those  of  the  intestine  (in  its  whole  length),  on  those  of  the  glandular 
reservoirs  (urinary  bladder),  as  well  as  on  the  secretory  organs  them- 
selves. In  brief,  it  may  be  said  that  no  organ  escapes  the  cerebral 
influence.  This  fact,  the  action  of  the  brain  on  the  nutritive  function, 
was  at  first  received  with  surprise  and  misgiving,  because  it  disagreed 
with  the  far  too  simple  idea  which  had  for  a  long  time  prevailed  con- 
cerning the  distribution  of  the  functions  between  the  two  great  divisions 
of  the  nervous  system. 

To  the  first  of  these  (cerebro-spinal  system),  of  which  the  brain  was  an  essential 
part,  were  assigned  conscious  vohmtary  acts  ;  to  the  second  (gi'eat  sympathetic 
system)  the  vmconscious  involuntary  phenomena  were  relegated. 

It  had  already  been  demonstrated  that  the  second  of  these  systems  (great 
sympathetic)  was  prolonged  into  the  former,  by  seeking  its  origins  in  the  spinal 
cord  ;  it  had  even  been  followed  higher  still  into  the  medulla  oblongata,  where 
important  centres  had  been  found  belonging  to  it.  But  however  high  it  might 
ascend,  no  one  ever  even  imagined  the  possibility  of  its  reaching  the  cerebral 
cortex,  this  being  reserved  by  definition  for  conscious  acts,  from  which  the  great 
sympathetic  system  is  exclvided.  As  a  matter  of  fact,  the  division  between  the 
two  is  not  such  a  simple  one,  and,  above  all,  is  not  made  according  to  a  plan 
sketched  out  below  the  cortex  or  at  some  distance  from  it.  A  large  number  of 
facts  go  to  prove  that  functional  acts  attain  their  highest  perfection  of  conscious- 
ness only  when  the  cerebral  cortex  participates  in  their  execution.  But  we  can- 
not admit  that  this  participation  of  the  cortex  necessarily  implies  a  conscious 
character  as  concerns  every  act  in  which  it  co-operates,  as  there  are  so  many 
examples  to  prove  the  contrary.     Further,  that  consciousness  may  in  no  degree 


472  SYSTEMATIC    FUNCTIONS 

exist  apart  from  the  co-operation  of  the  cortex  is  less  and  less  admitted,  transi- 
tion and  gradation  between  consciousness  and  unconsciousness  seeming  more 
probable  than  absolute  contrast  and  opposition  between  these  two  conditions. 

The  influence  of  the  cerebral  cortex  on  unconscious  movements  is  undeniable. 
The  difficulty  that  lies  before  us  is  to  know  to  what  circimistance,  or  to  what 
kind  of  organization,  is  due  the  fact  of  this  influence  being  of  a  different  nature 
from  that  exercised  by  the  cortex  on  the  muscles  of  the  life  of  relation.  A  parallel 
between  the  two  systems,  one  of  animal  and  the  other  of  vegetative  life  is  easy 
enough  to  draw  in  all  that  relates  to  the  two  sub-systems  or  inferior  arcs  which 
serve  them  as  a  basis,  and  this  parallelism  may  indeed  be  extended  to  a  certain 
distance  in  the  spinal  cord,  but  no  fixed  data  exist  with  regard  to  what  concerns 
the  superior  portions  of  both  these  systems. 

A.  Respiration. — The  movements  of  the  thorax  and  the  diaphragm 
correspond  to  several  functions,  of  which  two  of  the  principal  are  : 
pubnonary  veritilation,  and  the  emission  of  sounds.  In  the  spinal  cord, 
in  the  medulla  oblongata,  in  the  basal  ganglia,  and,  finally,  in  the  cortex 
itself,  the  associations  governing  these  two  kinds  of  movements  are 
effected.     Let  us  consider  principally  respiration. 

The  7nedidlary  centres  when  left  to  themselves  have  only  a  trace  of 
organization  as  concerns  respiration. 

The  bulbar  centre  and  the  nuclei,  both  inspiratory  and  respiratory, 
contained  in  it,  have  an  essential  action,  in  itself  sufficient  to  maintain 
the  regularity  of  the  respiratory  movements. 

The  cerebral  ganglia  and  the  cortex  have  an  action  not  absolutely 
necessary,  but  of  an  efficient  nature.  Emotional  disturbances  of  the 
respiration  have  caused  this  to  be  suspected,  and  stimulation  of  the 
parts  has  demonstrated  the  fact. 

Danilewsky,  Munck,  Bochefontaine,  rran9ois-rranck,  Bechterew 
and  Ostankow,  SjDencer  and  Horsley  have  observed  accelerations, 
slackenings,  and  stoppages  of  respiration  caused  by  localized  stimula- 
tion of  the  cerebral  cortex.  These  centres,  and  especially  that  of 
inhibition,  are  situated  in  the  antero-external  part  of  the  second 
and  third  convolutions. 

It  is  possible  to  follow  the  conducting  fibres  starting  from  this  area 
in  the  corona  radiata  where  the  impulse  will  find  them  again  and  will 
give  rise  to  the  same  effects.  They  usually  pass  through  the  knee  of 
the  internal  capsule. 

Movements  of  the  larynx. — These  are  of  two  kinds,  corresponding  to 
the  two  essential  functions  of  the  larynx,  respiratio7i  and  phonation. 
They  both  employ  most  of  the  muscles  of  the  larynx,  but  in  an  unequal 
manner.  The  first  consist  essentially  in  an  abdiLction  of  the  vocal 
cords,  which  causes  the  opening  of  the  glottis  at  each  movement  of 
inspiration  ;  the  second  in  an  adductio7i  of  these  parts,  with  contraction 
of  the  orifice  of  the  glottis.     For  both  of  these  movements  two  parallel 


SUPERIOR  SYSTEMATIZATIONS  473 

innervations  may  be  found,  and  these  may  be  followed  up  to  the  cortex. 
But  for  the  respiratory  movements  the  action  of  the  medulla  oblongata 
is  essential,  because  these  are  above  all  of  a  reflex  order  and  represent 
a  function  which  is  always  being  exercised  ;  for  the  movements  of 
phonation,  the  cortex  is  the  primum  movens.  These  centres  are  bi- 
lateral, that  is  to  say,  they  govern  two  sides  of  the  larynx  (at  least  in 
animals). 

If  the  before  mentioned  areas  of  the  brain's  surface  {gyrus  pre- 
crucialis)  have  been  laid  bare,  and  if  the  movements  of  the  glottis  are 
examined  under  stimulation  of  these  areas,  the  latter  will  be  seen  to 
open  during  movements  of  inspiration.  If  the  locahty  of  the  stimula- 
tion be  changed,  a  region  will  be  found  in  the  neighbourhood  (isthmus 
of  the  pre-crucial  gyrus)  which  closes  the  glottis,  producing  at  the 
same  time  acceleration  of  the  respiration  ;  it  should  correspond  to  a 
centre  of  phonation. 

B.  Circulation. — Hitzig,  Eulenbourg  and  Landois,  Bochefontaine, 
Lepine,  and  others  after  them,  have  observed  that  destruction  of  the 
excitable  area  (sigmoid  gyrus  in  the  dog)  is  followed  by  a  paralysis, 
which  is  not  only  motor,  but  is  also  vaso-motor ,  as  regards  the  areas 
corresponding  to  the  part  of  the  cortex  destroyed.  This  vascular 
paralysis  is  marked  by  an  elevation  of  temperature,  due  to  the  exagger- 
ation of  the  capillary  circulation,  and  to  the  resulting  loss  of  heat  in 
the  area  which  is  the  seat  of  this  hypersemia.  Without  being  exactly 
superposed,  the  motor  and  vaso-motor  centres  of  a  given  region  (of  a 
limb)  are  very  close  to  each  other,  and  arranged  nearly  in  the  same 
order.  Stimulation  of  the  cortex  may  cause  contraction  of  the  vessels 
(lower  the  temperature  locally)  to  the  same  extent  as  its  destruction 
causes  the  opposite  effect. 

Vaso-motor  area. — According  to  Bechterew  and  Mislawski,  the 
vaso-motor  area  of  the  cortex  extends  beyond  the  motor  area  ;  it  in- 
cludes not  only  the  sigmoid  gyrus,  but  also  a  territory  extending  behind 
it,  and  encroaches  even  on  the  temporal  lobe  (anterior  part  of  the  second 
and  third  primitive  convolution,  superior  part  of  the  fourth).  These 
authors  found  that  stimulation  of  the  posterior  portion  of  the  sigmoid 
gyrus  (behind  the  crucial  furrow)  caused  vaso-constriction  ;  that  of 
certain  portions  of  the  anterior  region  of  the  sigmoid  gyrus,  as  well  as 
some  points,  both  of  the  second  and  third  parietal  convolutions,  pro- 
duced vaso-dilatation.  Their  method  of  observation  consisted  in 
measuring  and  registering  the  general  arterial  pressure  ;  its  elevation 
indicating  a  constriction,  and  its  lowering  a  dilatation  of  the  peripheral 
vessels. 

Basal  ganglia. — Bechterew  and  Mislawski  have  also  observed  that 


474  SYSTEMATIC    FUNCTIONS 

stimulation  of  the  ganglia  of  the  base  of  the  brain  is  accompanied  with 
vaso-motor  effects  (constrictive),  these  effects  being  more  marked 
when  the  optic  thalamus  and  the  globus  pallidus  are  stimulated,  very 
feeble  when  other  parts  are  excited,  and  as  feeble  as  it  is  possible  for 
them  to  be  when  the  stimulus  is  applied  to  the  caudate  nucleus.  These 
effects  may  be  reproduced  by  the  stimulation  of  the  internal  capsule 
(principally  its  posterior  segment)  ;  and  they  are  also  observed  after 
degeneration  of  the  pyramidal  tract.  Thus  we  ascertain  the  fact  that 
the  basal  ganglia  are  united  to  the  subjacent  parts  by  special  fibres,  at 
the  same  time  that  they  exchange  impulses  with  the  corresponding 
cortex. 

Heart. — The  same  authors  have  observed  that  stimulation  of  the 
sigmoid  gyrus,  independently  of  its  merely  vascular  effect,  produces 
acceleration  of  the  heart  and  a  slowing  of  the  same  which  is  generally 
of  a  secondary  nature,  but  may  also  be  primary.  After  the  removal 
of  the  cortex  the  heart's  action  may  be  stopped  by  stimulation  of  the 
corona  radiata  at  a  point  corresponding  to  the  anterior  frontal  convolu- 
tion. The  tract  thus  stimulated  must  enter  into  the  construction  of 
the  cortico-thalamic  radiation,  as,  by  excitation  of  the  external  portion 
of  the  thalamus,  the  same  effect  of  stoppage  of  the  heart  in  diastole 
may  be  observed. 

Tarchanoff  recorded  the  case  of  a  young  man  who  possessed  the  faculty  of 
voluntarily  accelerating  the  beating  of  his  heart.  He  was  a  very  excitable 
subject.  He  could  also  move  certain  muscles  over  which  the  will  usually  has  no 
control,  such  as  the  muscles  of  the  extei'nal  ear. 

Thermo-regulative  function. — Between  the  circulatory  and  the  other  sensori- 
motor functions  demonstrated  by  these  experiments,  both  being  represented  in 
the  cerebral  cortex,  the  relations  are  very  numerous.  The  point  of  view  from 
which  they  can  be  most  distinctly  observed,  is  without  contradiction  that  of  the 
regulation  of  the  temperature,  or,  to  put  it  better,  the  equilibrium  between  the 
jDroduction  and  the  loss  of  heat  which  ensures  the  thermometrical  constancy  of 
the  organism. 

The  excitable  area,  in  so  far  as  it  is  motor  in  function,  produces  heat ; 
this  same  area,  in  so  far  a?  it  ii  vaso-motor,  preserves  (vaso-constriction)  or 
loses  (cutaneous  vaso-dilatation)  this  heat.  The  equilibrium  which  regulates 
this  heat  and  keeps  it  at  a  constant  level,  will  therefore  depend  on  an  agreement 
established  between  these  component  elements.  An  agreeiuent  like  this  between 
such  different  motor  effects  necessarily  presupposes,  in  the  living  being,  a  sensory 
phenomenon  naturally  capable  of  co-ordinating  them.  And  this  phenomenon 
is  not  lacking  here.  It  is  sensibility  to  heat  which  in  the  same  degree  as  the  other 
cutaneous  sensibilities,  appertains  to  the  tactile  area,  from  the  fact  of  its  sensori- 
motor nature.  The  cortex  may  certainly  contribute  to  the  regulation  of  the  tem- 
perature, and  may  take  part  in  the  struggle  against  cold  which  we  call  conscious. 
But  this  regulation  may,  and  usually  does  take  place  without  its  intervention, 
by  an  unconscious  process,  of  which  the  preceding  associations  give  us  merely 
a  model  in  the  order  of  consciousness.  In  the  basal  ganglia,  in  the  medulla 
oblongata,  even  in  the  spinal  cord  itself,  functional  connexions  arise,  whose 
aim  is  the  same,  and  of  which  certain  have  a  ])rei3onderating  influence. 


SUPERIOR  SYSTEMATIZATIONS  475 

C.  Digestive  functions. — The  brain  has  an  equal  influence  on  the 
digestive  functions,  as  will  be  seen  from  the  following  facts. 

Mastication,  deglutition. — By  stimulating  the  cortex  in  the  neigh- 
bourhood of  the  sigmoid  gyrus,  movements  of  the  niouth,  the  tongue 
and  the  jaws  are  produced  (Ferrier).  But  if  the  stimulus  is  brought 
to  bear  on  the  second  convolution  (that  enveloping  the  sigmoid  gyrus) 
in  the  exact  prolongation  of  the  crucial  furroAv,  genuine  masticatory 
movements  are  produced,  succeeded  by  deglutition  (Rethi).  Thus  a  pre- 
arranged association  is  brought  into  ])\ay,  which  is  controlled  by  this 
region  of  the  cortex  ;  this  association  produces  the  act  of  mastication. 
These  co-ordinated  movements  may  also  be  produced  by  stimulating 
the  subjacent  white  substance.  This  can  no  longer  be  done  when  the 
crura  cerebri  below  the  optic  thalamus  are  stimulated.  The  associa- 
tion, as  regards  its  most  essential  factors,  must  lie,  therefore,  either  in 
the  optic  thalamus  or  in  its  inferior  portion.  Stimulation  of  the  pos- 
terior part  of  the  floor  of  the  fourth  ventricle  also  provokes  swallowing. 
Stimulation  of  the  optic  thalamus  elicits  co-ordinated  movements  of 
mastication,  followed  by  deglutition  ;  it  also  affects  the  movements 
of  the  stomach  and  of  the  intestine.  This  ganglion  therefore  possesses 
great  importance  in  the  association  and  the  co-ordination  of  move- 
ments corresponding  to  the  vegetative  functions,  or  to  those  of  nutrition 
(Bechterew). 

Movements  of  the  stomach. — The  immediate  centres  of  the  organs 
we  are  now  about  to  mention  are  no  longer  situated  in  the  spinal  cord, 
but  in  the  ganglia  of  the  great  sj^mpathetic.  The  stomach  contains  a 
certain  number  of  these  disseminated  ganglia,  which,  though  much 
more  numerous,  call  to  mind  those  of  the  heart,  and  which  exist  in- 
dependently of  the  plexus  of  Auerbach.  These  ganglia  receive  the 
fibres  of  the  great  sympathetic  (properly  so  called)  and  also  of  the 
pneumogastric  and,  by  the  aid  of  the  nuclei  of  this  latter  contained  in 
the  spinal  cord  and  m  the  bulb,  they  are  attached  to  the  encephalic 
ganglia  and  to  the  cerebral  cortex.  Detailed  researches  have  been 
made  on  this  question  by  Openkowski,  Bechterew  and  Mislawski. 

In  the  spinal  cord  the  origins  of  the  nerves  of  the  stomacli  (splanchnic)  extend 
from  the  fifth  to  the  eighth  thoracic  pair  ;  the  fibres  iiniting  them  to  the  brain 
pass  into  the  anterior  columns.  They  represent  an  important,  and  indeed  an 
essential,  reinforcement  of  the  ganglia  of  the  base  :  caudate  nucleus,  lenticular 
nuclevis  and  corpora  quadrigemina  ;  they  are  connected  with  the  cortex.  Special 
innervations  for  the  cardiac  orifice,  the  body  of  the  stomach,  and  the  pylorus 
must  be  distinguished. 

Cardiac  orifice. — Its  centre  of  dilatation  is  at  the  union  of  the  antero- 
inferior extremity  of  the  caudate,  and  lenticular  nuclei  near  to  the 


i76  SYSTEMATIC    FUNCTIONS 

anterior  commissure  ;  it  acts,  through  the  vagus  and.  sympathetic 
nerves  and  their  terminal  gangha,  by  relaxing  this  orifice  ;  this  centre 
is  united  to  an  area  of  the  cortex  situated  in  the  neighbourhood  of  the 
crucial  furrow.  The  two  splanchnics,  large  and  small,  which,  arising 
from  the  sympathetic  chain  are  in  part  distributed  to  the  stomach, 
thus  participate  in  this  innervation  ;  the  large  splanchnic  as  a  centri- 
fugal, and  the  small  splanchnic  as  a  centripetal  nerve,  by  a  reflex  cycle. 
The  opening  of  the  cardiac  orifice  may,  however,  ensue  in  a  reflex 
manner  by  stimulation  of  a  large  number  of  organs,  including  the 
viscera. 

Body  of  the  stomach. — The  muscles,  ganglia,  and  nerves  are  less 
numerous  here  and  less  powerful  ;  the  movements  are  also  less  ener- 
getic, and  consist  of  rhythmical  and  peristaltic  waves  going  from  the 
cardiac  orifice  to  the  pylorus.  These  movements  are  governed  by  the 
vagus  and  the  principal  encephalic  centre  is  in  the  corpora  quadri- 
gemina.  An  inhibitory  action,  antagonistic  to  the  preceding,  is  exer- 
cised by  the  splanchnics,  and  controlled  by  the  spinal  cord.  No  con- 
nexion of  these  centres  with  the  cortex  as  regards  the  body  of  the 
stomach  has  been  discovered,  but  only  for  its  pyloric  portion,  a  general 
contraction  of  which,  with  cessation  of  the  rhythmic  movement,  can 
be  induced  by  stimulation  of  the  sigmoid  gyrus  (Bechterew  and  Mis- 
lawski). 

Pylorus, — In  this  locality  the  muscles  are  powerful  and  the  ganglia 
are  numerous,  innervation  giving  rise  to  relatively  energetic  move- 
ments. The  vagus  and  the  sympathetic  govern  these  movements  by 
means  of  the  splanchnics.  These  nerves  are,  in  the  pylorus,  made  up 
of  a  mixture  of  excitatory  and  inhibitory  fibres,  of  which  one  or  the 
other  predominate,  according  to  the  animal. 

The  centre  for  dilatation  of  the  cardiac  orifice,  either  that  situated 
in  the  cortex  or  that  located  in  the  corpus  striatum,  is  a  constrictive 
centre  for  the  pylorus  ;  a  centre  of  dilatation  for  this  sphincter  is,  on 
the  other  hand,  located  in  the  corpora  quadrigemina. 

Movements  of  the  intestine. — -These  have  been  studied  by  Bechterew 
and  Mislawski  ;  the  general  outline  of  their  work  is  the  same  as  that 
given  above.  The  small  intestine  is  innervated  by  the  sympathetic 
and  the  vagus.  The  first  of  these  nerves  is  especially  inhibitory  in 
action,  the  second  chiefly  motor,  as  in  the  case  of  the  stomach.  The 
sympathetic  elements  leave  the  spinal  cord  from  the  sixth  dorsal  up 
to  the  first  lumbar. 

The  large  intestine  is  innervated  by  the  great  sympathetic,  and  by 
the  erector  nerves  which  go  to  the  hypogastric  plexus.  The  origins  of 
the  sympathetic  elements  are  in  the  first  lumbar  pairs  ;    the  erector 


SUPERIOR  SYSTEMATIZATIONS  477 

nerves  come  from  the  first,  second  and  third  sacral  pairs.  In  ascend- 
ing from  the  intestine  to  the  cerebral  cortex,  we  traverse  the  terminal 
plexuses  (of  Auerbach  and  of  Meissner),we  follow  either  the  branches 
of  the  vagus  or  those  of  the  great  sympathetic  (splanchnic  nerve),  we 
pass  through  the  dorsal  and  cervical  part  of  the  spinal  cord,  and  also 
of  the  bulb,  and  finally  we  find  in  the  optic  thalamus  an  essential  centre 
of  association,  not  only  for  the  movements,  but  also  for  the  secretions 
of  the  intestine. 

It  is  for  this  reason  that,  in  birds,  if  the  optic  thalami  are  removed 
at  the  same  time  as  the  hemispheres,  all  food  remains  in  the  gizzard  ; 
serious  digestive  disturbances  ensue,  and  the  animal  finally  dies  of 
starvation.  If  the  optic  thalami  are  preserved  life  may  last  a  very 
long  time,  provided  food  is  given  artificially.  If,  in  mammals,  the 
optic  thalamus  is  uncovered,  the  lateral  ventricle  opened,  and  the 
hemispheres  are  removed  and  stimulation  is  brought  to  bear  on  these 
gangha  by  the  help  of  fine  electrodes  sunk  in  their  substance,  either 
movements  of  the  intestine  result,  or  relaxation  of  its  walls  and  stoppage 
of  the  peristaltic  contractions.  Stimulation  of  the  middle  region  of 
the  thalamus  rather  tends  to  strengthen,  though  inconstantly,  the  move- 
ments of  the  intestine,  both  peristaltic  and  rhythmic.  That  of  the 
external  nucleus  relaxes  the  wall  of  the  small  intestine,  and  arrests  the 
peristaltic  movements.  That  of  the  antero-external  region  acts  on  the 
large  intestine,  whose  movements  it  stimulates  up  to  the  point  of  caus- 
ing defecation.  The  proximity  of  these  two  segments  makes  it  some- 
times possible  to  obtain  simultaneously  the  two  effects,  namely  : 
relaxation  of  the  small  and  contraction  of  the  large  intestine. 

On  the  cortex,  in  the  sigmoid  gyrus  and  the  posterior  part  of  the 
second  convolution  which  encloses  it,  areas  are  to  be  found  stimulation  of 
which  induces  the  whole  series  of  preceding  effects,  but  more  often 
those  Hmited  to  certain  regions  of  the  two  intestines  ;  with  these 
peculiarities,  however,  that  the  effects  are  feebler,  the  latent  period 
longer,  and  the  excitability  of  the  grey  substance  much  more  quickly 
exhausted. 

Sphincter  of  the  anus. — In  inferior  mammals  the  sphincter  of  the 
anus  may  be  caused  to  contract  by  stimulating  the  cortex  a  little  be- 
hind the  crucial  furrow  on  the  posterior  segment  of  the  sigmoid  gyrus, 
near  to  its  external  border  (J.  Meyer).  In  the  monkey,  the  ano-cortical 
centre  is  on  the  posterior  portion  of  the  paracentral  lobe  (Sherrington). 
The  ganghonic  reinforcement  of  the  base  of  the  brain  corresponding 
to  this  innervation  has  not  yet  been  determined,  but  owing  to  the 
experiments  of  Goltz,  its  medullary  reinforcement,  or  ano-spinal  centre 
is  known,  this  being  situated  in  the  lumbar  spinal  cord,  at  the  level  of 


478  SYSTEMATIC    FUNCTIONS 

the  sixth  and  seventh  vertebrae  in  the  rabbit,  and  of  the  fifth   in  the 
dog. 

The  functional  antagonism  between  the  anal  sphincter  and  the  ex- 
pulsive muscles  of  the  rectum  is  also,  in  a  certain  degree,  displayed 
anatomically  by  the  provision  of  definite  fibres  which  proceed  to  the 
first  and  second  of  these  muscles.  The  law  laid  down  above  requires 
that  the  transverse  fibres,  those  of  the  sphincter,  should  be  chiefly 
innervated  by  the  branches  of  luml)ar  origin,  emanating  from  the 
sympathetic  chain  (inferior  mesenteric  ganglion  and  nerve),  and  that 
the  transverse  fibres  of  the  rectum  should  be  chiefly  supplied  by  those 
arising  from  the  sacral  spinal  cord.  In  reality  there  is  a  mixture  of 
elements,  and  the  hemorrhoidal  or  anal  nerve  (of  sacral  origin)  is  the 
constrictor  of  the  anus. 

Rhythmical  contractions  of  the  anal  sphincter. — After  the  removal  of  the  ano- 
cortical  centre,  rhythmical  contractions  of  the  sphincter  of  the  anus  may  be 
observed  (V.  Ducceschi)  which  others  have  noticed  after  the  removal  of  the  spinal 
cord  in  its  inferior  portion  (Goltz  and  Ewald).  These  contractions  are  difficult 
to  explain  ;  they  may  possibly  be  attributed  to  an  abnormal  transmission  to  its 
sphincter  of  the  rhythmical  excitations  of  the  intestine.  The  anal  sphincter  is, 
however,  a  special  muscle  ;  although  belonging  to  the  intestine,  it  is  made  up  of 
striated  fibres.  It  is  obedient  to  the  will,  thovigh  at  the  same  time  being  an  organ 
whose  action  is  especially  tonic  and  reflex.  It  resembles  the  diaphragm,  which 
is  also  a  voluntary  and  automatic  muscle,  and  one  which,  like  the  anal  sphincter, 
contracts  rhythmically  after  being  excised. 

D.  Secretions. — Bochefontaine  and  Lepine  have  observed  that 
stimulation  of  the  cortex  applied  to  the  sigmoid  gyrus  and  neighbour- 
ing parts  causes  the  salivary  glands  to  secrete  in  a  bilateral  or  rather 
a  crossed  manner.  Bochefontaine  has  also  observed  that  stimulation 
of  the  motor  area  in  the  dog  influences  the  biliary  secretion  of  the  liver, 
and  also  the  secretion  of  pancreatic  juice,  both  of  which  secretions  it 
diminishes.  The  same  author  has  further  observed  contraction  of  the 
spleen  to  follow  stimulation  of  the  anterior  part  of  the  brain.  At 
several  points  (1,  3,  4,  11  of  D.  Ferrier)  Bechterew  and  Mislawsky  have 
provoked  the  secretion  of  tears,  by  stimulating  the  cortex  at  the  sigmoid 
gyrus  in  the  interhemispherical  fissure,  that  is  to  say,  by  bringing  the 
stimulation  to  bear  on  the  internal  part  of  the  ayiterior  and  posterior 
convolutions  of  this  gyrus.  Excitation  of  the  convexity  of  the  gyrus 
has  only  a  very  feeble  action  ;  and,  apart  from  it,  nothing  is  produced 
in  this  direction.  The  effect  is  bilateral,  but  less  on  the  side  submitted 
to  excitation.  At  the  same  time  dilatation  of  the  pupils,  accompanied 
by  projection  of  the  ocular  globes,  and  shrinkage  of  the  third  eyelid 
may  be  observed  ;  these  phenomena  always  appearing  earlier  on  the 
side  opposite  that  stimulated. 

If,  once  more,  we  leave  the  peripheral  organs,  in  order  to  ascend  to 


SUPERIOR  SYSTEM ATIZATIONS  479 

the  cortex,  by  following  the  paths  of  the  impulse,  we  shall  find,  in  the 
neighbourhood,  or  even  in  the  substance,  of  the  glands,  ganglia  of  the 
great  sympathetic  ;  from  these  spring  branches,  either  direct  (visceral) 
or  indirect  (intermingled  with  mixed  trunks)  which  are  detached  from 
the  chain  and  have  their  origins  in  the  spinal  cord,  or  else  branches  of 
the  cranial  nerves  (chorda  tympani),  which  are  the  equivalents  of  the 
branches  of  the  great  sympathetic  in  this  region.  Afterwards  from 
the  bulbar  or  medullary  centres  we  ascend  to  a  ganglionic  reinforcement 
or  centre  of  association,  this  being  constant  for  all  functions  of  this 
order  and  having  an  exceptional  importance  in  the  government  and 
the  regulation  of  nutritive  phenomena  ;  this  is  the  optic  thalamus. 
From  this  we  reach  the  cortex  of  the  brain. 

Lachrymal  secretion. — The  lachrymal  secretion,  in  particular,  displays 
this  succession  and  this  concatenation  in  a  very  distinct  manner.  It 
is  governed,  starting  from  the  spinal  cord  and  the  bulb,  by  that  part 
of  the  great  sympathetic  which,  arising  from  the  superior  thoracic 
spinal  cord,  ascends  along  the  cervical  chain  as  far  as  the  trigeminal 
nerve.  Some  elements  come  from  the  medulla  oblongata  by  the 
trigeminal  itself  (strengthening  origins),  and  all  of  them  proceed  to  the 
gland  by  the  lachrymal  branch  of  the  ophthalmic  division.  The  greater 
or  lesser  part  taken  by  one  or  the  other  origin  in  lachrymal  innervation 
is  the  only  point  which  gives  rise  to  differences  of  opinion  on  this  sub- 
ject. The  original  nuclei  of  these  bulbo-medullary  nerves  are  attached 
to  the  optic  thalamus,  which  forms  a  centre  of  reflexion  of  great  im- 
portance for  the  lachrymal  secretion.  The  direct  stimulation  of  the 
optic  thalamus  at  its  lower  and  internal  portion,  near  the  grey  com- 
missure, is  followed  by  secretion  of  tears  on  both  sides  (predominance 
of  the  opposite  side)  with  dilatation  of  the  pupils  and  protrusion  of 
the  eyeballs. 

Stimulation  of  the  cortex  in  i  ^  K^eiuxe-mentioned  points  of  the  gyrus 
has  the  same  effect. 

The  lachrymal  secretion  thus  provoked  by  stimulation  of  the  optic  thalamus 
and  the  cerebral  cortex  resembles  that  which  accompanies  certain  psychical 
processes  (emotions).  Salivation  is,  on  the  other  hand,  a  symptom  of  certain 
mental  or  nervous  affections  (Esquirol,  Fodere  .  .  .).  It  is  also  observed  in 
epilepsy  during  the  attacks,  or  in  the  form  of  crises  equivalent  to  these  attacks 
themselves  (A.  Koranyi,  Ch.  Fere).  On  this  point  it  is  necessary  to  notice  the 
difference  in  the  natvire  and  appearance  of  the  saliva,  according  to  the  conditions 
of  its  secretion,  its  glandular  origin,  and  the  locality  of  the  excitations  provoking 
this  secretion.  A  similar  gland,  the  sub-maxillary,  yields  either  a  viscous  or 
watery  saliva  according  to  which  of  its  two  secretory  nerves,  the  great  sympa- 
thetic or  the  chorda  tympani,  is  stimulated.  The  first  is  usually  called  "  sympa- 
thetic saliva,"  and  the  second  "  cerebral  saliva,"  but  tliis  is  most  incorrect,  inas- 
much as  the  two  nerves  are  ganglionic  and  similar  to  each  other,  one  coming 


sp: ^ 


4  tkt 


nkaieal 


SUPERIOR  SYSTEMATIZATIONS  481 

the  spinal  cord  by  means  of  the  gangha  of  the  sympathetic  chain  pro- 
ceeding from  the  second  lumbar  to  the  fourth  sacral.  Stimulation  of 
the  communicating  branches  of  the  sacral  nerves  also  reinforces  the 
vaginal  movements  (Langley).  As  regards  the  vaso-motor  pheno- 
mena, they  are  under  the  control  of  the  nerves  following  the  same 
paths,  and  of  which  some  cause  vaso-dilatation  (third  and  fourth 
sacral),  others  vaso-constriction  (first  and  second  sacral).  Further- 
more, this  system  of  nerves  also  supplies  the  penis. 

The  movements  of  the  vagina  are  affected  by  stimulation  of  the 
sigmoid  gyrus  either  in  the  direction  of  augmentation  (stimulation  of 
the  posterior  region),  or  in  that  of  arrest  (stimulation  of  the  antero- 
external  region),  though  no  definite  distinction  exists  between  the 
areas  producing  these  contrary  results. 

These  effects  are  also  produced  when  the  anterior  half  of  the  optic 
thalamus  is  stimulated  in  the  neighbourhood  of  the  area  which  presides 
over  the  bladder  and  rectum.  These  grey  masses  are  connected  mth 
the  great  sympathetic  by  bulbar  and  spinal  centres,  stimulation  of 
which  also  acts  either  by  inhibiting  or  by  provoking  movements,  yet 
with  certain  differences  in  the  character  of  these  movements,  which 
vary  according  to  the  different  areas  stimulated  (Bechterew  and 
Mislawsky). 

Persistent  influence  of  the  brain  on  the  spinal  cord. — Sensory  impressions,  more 
especially  when  of  a  lively  nature,  exert  on  the  superior  centres  (notably  on  the 
brain),  an  effect  which  may  persist  long  after  they  themselves  have  disappeared. 
As  regards  motor  impressions  leaving  the  brain  to  proceed  to  the  spinal  cord,  it 
is  generally  maintained  that  theii-  effects  scarcely  survi\-e  their  disappearance. 
Brown-Sequard,  R.  Dubois,  Tissot  and  Contejean  bring  forward  facts  wlxich 
tend  to  show  that  the  spinal  cord  may  retain  something  of  these  effects  even 
after  removal  of  the  brain.  Tlie  first  of  these  organs,  therefore,  appears  to 
possess  a  certain  faculty  for  the  preservation  of  stimuli,  though  much  restricted 
in  comparison  with  that  of  the  second. 

Examples. — A  duck  from  which  one  of  the  two  hemispheres  has  been  removed 
walks  obliquely  on  acct)imt  of  the  paresis  of  the  miiscles  of  the  side  opposite  to 
the  lesion.  If  the  cervical  spinal  cord  be  cut  across  and  the  animal  be  placed  in 
water,  it  will  swim,  and  in  swimming  will  follow  an  oblique  direction.  The 
ablation  of  the  whole  of  the  encephalon  does  not  have  the  effect  of  re-establishing 
equilibrium,  a  proof  that  the  want  of  equilibrium  has  been  felt  by  the  spinal  cord 
and  is  persistent  after  the  suppression  of  the  jDortion  primarily  injm-ed. 

If  the  motor  area  of  the  cortex  on  the  left  side  be  removed  in  a  dog  affected 
with  St.  Vitus's  dance,  it  will  be  seen  that  the  clonic  attacks  are  augmented  on 
the  right  side  and  preserve  the  same  intensity  on  the  left.  If,  later,  the  spinal 
cord  below  the  medulla  oblongata  be  cut  across  and  artificial  respiration  be 
practised,  it  will  be  seen  that  the  attacks  of  chorea  remain  stronger  on  the  right 
than  on  the  left  side. 

Trophic  influence  of  the  brain. — The  experimental  analysis  to  which  the  cere- 
bral functions  have  been  submitted  has,  in  the  fu-st  instance,  displayed  the 
relations  of  the  brain  with    the  muscular  tissue,  whose  functional  activity  it 

V.  I  I 


482  SYSTEMATIC    FUNCTIONS 

regulates  ;  later,  these  relations  have  been  extended,  like  those  of  the  nervous 
system  itself,  to  a  large  niunber  of  other  tissues  (vascular  and  visceral  muscles, 
visceral  and  cutaneous  glands,  etc.)-  This  analysis  is  foimded  on  the  anatomical 
division  of  our  tissues  into  special  cellular  orders  very  easy  of  recognition.  But 
it  is  possible  to  proceed  in  a  different  manner.  It  is  possible  to  take  as  a  test  of 
the  brain's  activity,  not  the  different  tissues  which  are  to  an  unequal  degree 
dependent  upon  it,  but  the  substances  excreted  by  the  emunctories  of  the  organ- 
ism, which  substances  reveal  the  activity  of  the  organism  as  a  whole,  and  can 
therefore  give  us  information  with  regard  to  the  influence  exerted  by  the  brain 
on  this  activity. 

This  is  the  aim  which  Belmondo  has  in  view.  Brought  back  to  the  simplest 
terms,  excretion  presents  itself  imder  two  forms  having  two  distinct  situations. 
The  lung  is  the  emunctory  of  carbon  (carbonic  acid)  ;  the  kidney  is  the  emunctory 
of  nitrogen  (urea  and  similar  bodies).  The  experiment  consists  in  measuring  the 
gases  of  respiration,  and  also  the  total  amount  of  nitrogen  in  the  urine,  first  in 
the  normal  state  and  secondly  after  removal  of  the  hemispheres.  This  experi- 
ment has  been  performed  on  pigeons,  on  which  ablation  with  subsequent  survival 
is  easily  performed. 

a.  Excretion  of  carbon. — The  experiments  of  G.  Corin  and  A.  van  Beneden  had 
already  shown  that  the  removal  of  the  cerebral  hemispheres  in  pigeons  does  not 
sensibly  modify  the  excretion  of  carbonic  acid  (nor  the  temperature)  ;  we  have 
only  to  ascertain  the  facts  with  regard  to  the  secretion  of  nitrogen.  The  experi- 
ment must  necessarily  be  made  on  animals  in  a  fasting  condition,  as  during  diges- 
tion, as  is  well  known  (in  certain  conditions),  a  notable  quantity  of  nitrogen 
arising  directly  from  the  food  is  added  to  the  quantity  produced  by  the  dis- 
assimilation  of  the  tissues,  and  this  must  be  eliminated. 

b.  Excretion  of  nitrogen. — Compared  in  fasting  pigeons,  some  healthy  and 
others  deprived  of  the  cerebrum,  the  excretion  of  nitrogen  varies  considerably, 
even  to  the  point  of  being  reduced  in  the  second  to  less  than  half  the  value  it  has 
in  the  fii'st.  To  put  it  otherwise,  the  brain  governs  in  a  certain  manner  and  to  a 
certain  degree  the  excretion  of  nitrogen  since,  if  it  be  removed,  this  excretion  is 
diminished. 


Nitrogen  eliminated  per  kilogramme  and  per  24  hours. 

„         „     ^  ,  r  r     i.  (Healthy  pigeons 0-57 

Four  first  days  of  fast  (pi^eo^g  ^^ith  cerebrum  removed      .      .      .      0-27 

Ratio 0-47 

The  two  principal  excretions  of  the  organism,  carbonic  acid  by  the  lungs, 
nitrogen  by  the  urine,  have  each  a  different  signification.  The  first  represents 
and  measures  the  waste  of  energy  of  the  organism  :  its  principal  soiu-ce  lies  in  the 
work  of  the  muscles  (although  that  of  the  other  tissues  helps  slightly  in  the 
process)  ;  it  is  irregular,  as  are  also  the  intermissions  of  this  work  itself.  The 
second  represents  and  measures  the  work  of  disassimilation  of  the  tissues 
(including  the  muscular)  ;    it  is  constant  as  is  this  disassimilation  itself. 

In  animals  in  a  state  of  repose  (in  cages),  the  waste  of  energy  is  the  same  (very- 
much  reduced),  whether  they  retain  the  brain  or  not.  The  difference  is  only 
marked  when,  the  movements  of  both  being  rmrestrained,  the  animals  with 
brain  intact  can  show  their  spontaneity.  In  the  same  animals  in  repose,  some 
with,  and  others  without  the  brain,  we  see,  on  the  contrary,  that  disassimilation 
is  much  diminished  in  the  last-named,  and  this  is  a  new  fact  brought  out  promin- 
ently by  these  experiments.     Thus  the  brain,  which  before  had  only  been  credited 


SUPERIOR  SYSTEAL\TIZATIONS  483 

with  the  possession  of  relations  witJi  the  muscular  tissue,  is  now  seen  to  extend 
its  action  to  the  other  tissues.  Fiu"ther,  it  not  only  regulates  the  waste  of  energy 
properly  so-called  (oxydation  of  the  carbo-hydrates),  but  it  also  governs  the 
molecular  renewal  of  the  elements  (liistolysis,  dislocation  of  the  albiimhioids). 

The  regulative  action  of  the  waste  of  energy  is,  in  certain  determinate  condi- 
tions, a  conscious  one.  That  of  disassimilation  is  unconscious,  and  operates  in 
the  same  way  as  ordinary  reflex  actions. 

It  must  be  admitted  that  any  plausible  explanation  of  the  mechanism  em- 
ployed by  the  brain  in  the  control  of  tissue  disassimilation  is  absolutely  lacking. 
In  fact,  though  we  are  acquainted  with  nerves  whose  stimulation  has  for  direct 
effect  the  augmentation  of  the  waste  of  energj^  in  the  tissues  and  is  displayed  by 
an  exaggeration  of  the  excretion  of  carbonic  acid  (for  example,  motor  nerves  of 
the  muscles),  we  know  of  none  whose  excitation  would  create  an  augmentation 
of  their  histolysis,  to  the  extent  of  causing  an  exaggeration  of  the  nitrogenous 
excretion.  The  relationship  existing  between  the  brain  and  what  is  called  nutri- 
tion of  the  tissues  (a  relationship  which  facts  seem  to  demonstrate,  and  which 
we  have  no  reason  to  deny),  cannot  be  interpreted  in  so  clear  a  manner  as  can 
that  existing  between  the  brain  and  ordinary  movement.  Experimentally  and 
logically,  the  intermediaries  are  rmlino-n-n  to  us. 

As  a  set-off,  Goltz  has  observed  in  a  dog  from  which  he  had  removed  the  cere- 
bral cortex  great  voracity  and  an  exaggerated  consumption  of  food.  It  is  true 
that  a  notable  part  of  this  food  must  have  been  wasted,  on  account  of  incomplete 
digestion.  However,  the  results  of  experiments  differ  from  several  points  of 
view.     This  question  demands  fresh  investigation. 

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484  -       SYSTEMATIC    FUNCTIONS 

Internal  capsule    and  centrum  ovale.— Carville  et  Duret,    Arch,    de    Phys.,   1875, 

P    136 Etienne,  Monoplegie  faciale  et  dev.  conjug.  des  yeux,  Presse  med.,  1896. — 

FiTBES    Arch.  din.  de  Bordeaux,  1893.— Veyssi^re,  Arch,  de  Phys.,  1874,  p.  288. 

Corpus    callosum. — Lo   Monaco,   Calleux   et  gangl.  basilaires,  Arch.  ital.  de    biol, 

1897  t   XXVII,  p.  29G. 

Comparative  anatomy.— Ad.  Bary.,  Develop,  des  centres,  Arch.  f.  An.  und  Phys., 

1898  — Chatin,  Homologies,  poissons,  C.  R.  Ac.  sc,  1889,  t.  CVIII,  p.  628.— Dhkre  et 
L\picque  Arch  de  Phys.,  1898,  p.  763.— Faivre,  Insectes  centres  nerv.  mouv.  rota- 
toire  G  R.  Ac.  sc,  1875,  t.  LXXX,  p.  739,  1149  et  1332.— Fritsch,  Homologies,  Arch, 
f  An  und  Phys.,  1877.— Giacomini,  Microcephales,  Arch.  ital.  de  biol.,  1891,  t.  XV,  p.  63. 
— Lussana,  Neiu-ophys.  comp..  Arch.  ital.  de  biol,  1883,  t.  IV,  p.  283.— Schlapp,  Differ, 
de  struct.  irc7i. /.  .4«.  tmcZ  P/iys.,  1898,  p.  381.  ,     ,    r ■    ,    ^     i,-  ,     looo 

Excitability  of  the  cortex — different  mfiuences. — Aducco,  Arch.  ital.  de  biol,  1889, 
t   XI   p.  192,  1891,  p.  136,  et  1893,  p.  1. — Axenfeld,  Subst.  chim.,  Arch.  ital.  de  biol., 

1895 't.'xxil,  p.  60. Bechterew,  Inflammation,  Messager  neurol.,  Kazan,  1894. — 

BoCHEFONTAiNE,  Deplacenient  des  points  excitables,  Arch,  de  Phys.,  1883,  p.  28. — 
Br  -Sequabd,  Vivisect,  sm-  homme.  Arch,  de  Phys.,  1875  et  1890,  p.  762.— Cabvalho, 
Cocaine  BioL,  1888,  p.  664.— Charpentier,  Cocaine,  Biol,  1884,  p.  758.— Couty,  Biol, 
1880  p.'  44  ;  'l886,  p.  164. — Danillo,  Alcool  ;  absinthe,  Biol,  1882,  p.  83. — Fbanck 
et  PiTRES,  Arch,  de  'phys.,  1885  ;  Biol,  1878  et  suiv. — Heimann,  Wirkung  d.  Drucks  .  .  . 
Arch  f  An  und  Phys.,  1884. — Joukoff,  Arret  de  la  circul.  cereb.,  Bolnitch.  Gaz.  Bot., 
1895-  Gliniq.  malad.  menl,  Saint-Petersboiirg,  1895.— Langlois,  Centres  psycho-mot. 
nouveaunes,  Biol,  1889  p.  503.— Munck,  Anemie,  Arch.  f.  An.  und  Phys.,  1883.— 
Openchow-ski,  Act.  du  froid,  Biol,  1883.— Orchansky,  Anemie,  Arch.  f.  An.  und  Phys., 

1883 Teschich,  Arch,  de  Phys.,  1885. — Thomasini,  Section  des  racines  posterieures. 

Arch  ital  de  biol.,  1895. — F.  Franck  et  Pitre.s,  Div.  communications,  Biol,  1878. — 
De  Varigny,  C.  R.  Ac.  sc,  1884. — Vulpian,  Duree  apres  la  mort,  G.  R.  Ac.  sc,  ISSb. 

Mechanical'  stimulation  of  the  brain,— Couty,  Biol,  1880,  p.  46  ;  excitation  ther- 
mique,  Biol,  1886.— Luci.ani,  Arch,  ital  de  biol,  1883,  IV,  p.  268.— Vulpian,  G.  R. 
Ac.  sc,  diverse  notes,  1885.  -^^  ^     ,  , 

Anatimico-clinical  methods  of  observation.— Charcot  et  Pitres,  Arch,  neurol, 
XXVII,  86,  1894. 

Inhibitory  power  of  the  cortex. — Fano,  Arch,  ital  de  biol,  1895,  t.  XXIV,  p.  438. 

LiBERTiNi,  Arch,  ital  de  biol,  1895,  t.  XXIV,  p.  438. 

Latent  period. Fr.-Franck,  Localisat.   cerebr. — Novi  et  Gbandis,  Arch,  ital    de 

biol,  1888,  t.  X,  p.  314. — De  Varigny,  Arch,  de  Phys.,  1885. 

Refractory  period. — Bboca  et  Richet,  Biol,  1896. 

Cerebral  localizations. — Discussion. — Axbebt,  Wien.  med.  Presse,  1895. — V.  Bobos- 
nyai  Luchsingeb,  Steger,  Pestalozzi,  Hermann,  Arch.  v.  Pfluger,  1875,  t.  X,  p.  77  ; 
Bybo'n  Bbamwell,  Se7n,  med.,  1896.— Chabcot,  Biol,  1875,  1876.— Couty,  Arch,  de 
Phvs  1883  •  G  R  Ac  sc,  1879  et  1881. — Chabcot  et  Pitres,  Arch.  din.  de  Bordeaux, 
septembre,  1894.— Debierre,  Biol,  1888.— Dupuy,  Biol,  1875,  1886,  1887,  1888.— 
Duval,  Rapport  d'une  commission,  Biol,  1886,  p.  371. — Eisenlohb,  Deutsch.  Zeitsch. 
f.  nerv.'Heilkunde,  1893. — S.  Exner,  Journ.  of  Phys.,  1880. — Golgi,  Arch,  ital  de  biol, 

1888. HuGLiNGS   Jackson,   Fragments  neurologiques.   Lancet,    1893. — Jackson    (de 

Boston),  Perforation  du  crane  de  part  en  part,  pas  d'aphasie,  survie  10  ans,  attaque 
d'epilepsie,  Biol,  1871,  p.  169. — Marcacci,  Biol,  1882;    .4rc7i..  ital  de  biol,  1882,  t.  I 

et  II. Ma'rinesco,  Revue,  Sem.  med.,  avril,  1896. — Munck,  Critiq.  des  vues  de  Goltz, 

Soc  de  phys.  de  Berlin,  avril,  1896.— Pick,  Prazer  Zeitsch.  f.  Heilk.  X,  1,  138.— Pitres, 
Biol,   1876  ;    Gongres  de  Nancy,   1896.— Schiff,  Lez.  de  Fisiol.  sist.  nerv.  encefalico, 

Firenze,  1873. 

Localization  of  speech.— Bouillaud,  G.  R.  Ac  sc,  1873.— Broca.— Chevreul, 
G.  R.  Ac  sc,  1873. — Fournie,  G.  R.  Ac.  sc,  1873. 

Cerebral  localizations — Motor  centres. — Bechterew,  Excit.  chez  I'homme,  Arch, 
f.  An.  und  Phys.,  1889,  sup.  p.  943. — Carville  et  Duret,  Arch.  Phys.,  1875. — Couty, 
Arch.  Phys.,  1879,  1881. — Couty  et  Lacerda  .  .  .  Curare  .  .  .,  G.  R.  Ac.  sc,  1880, 

t.  XCI. Ed.  Hitzig,  Reich,  und  Du  Bois  R.  Arch.,  1870,  Heft  3  et  4  ;    Unters.  ub.  d. 

Gehirns  (Abhandl.  physiol.  und  path.  Inhalts),  Berlin,  1874. — G.  Fritsch  imd  Ed. 
Hitzig  Ueb.  elektrish.  Erregb.  der  Grosshirns,  Reich,  und  Du  Bois  R.  Arch.,  1870,  Heft  3. 

Ferrier,  Brit.  med.  Journ.,  avril,  1873  ;  Progres  med.,  1873.— H.  Jackson,  Med.  Tim. 

and  Gaz.,  1861  et  suiv. — Lepine,  These  agregation,  1875. — Lussana  et  Lemoigne,  Arch. 
Phys.,  1877,  p.  119.  .     ,      .     . 

Localization  of  general  sensibility  and  of  temperature. — Bechterew,  Arch.  f.  An. 
und  Phys.,    1900,  p.   22. — Brissaud,  Legons  Salpetriere. — Br.-Skquabd,   Anesth6sie, 

Biol,   1883. Da'rkschevitsch,  Neurol  Centralbl,   1890. — Dana,  Journ.  of  nerv.  and 

ment.  dis.,  1894  ;  Medic.  Record,  N.  York,  1893. — Dejerine,  Revue  neurol,  mars,  1893  -, 
Etude  sur  I'aphasie,  Revue  de  med.,  1885  ;   Arch.  Phys.,  II,  588.— Dessoie,  Arch.  f.  An. 


SUPERIOR  SYSTEMATIZATIONS  485 

undPhys.,  1893,  p.  525.— Dupuy,  Biol.,  1886.— Ferriee  et  Yeo,  1875  a  1884.— Fea2^ck 
HocHWAiiT,  Soc.  med.  de  Vienne,  1893  ;  Internat.  klinish.  llundschau.  No.  9,  1893. — 
Feanck,  S.  Madden,  Joiirn.  of  nerv.  and  ment.  dis.,  1893.^ — Maeinesco,  Revue,  Sent. 
med.,  1896. — W.  Mott,  Journ.  of  Phys.,  1894. — H.  Munck,  Ueb.  die  Funct.  der  Gross- 
hirn.,  1890  ;  Ueb.  die  Fiihlensphar.,  1892.— Ransom,  Brain,  1892.— J.  Souey,  Bev. 
gen.  des  sc. — Schaffee,  Journ.  of  Phys.,  1898. — R.  Tkipiee,  Congres  de  Geneve  ;  Bevue 
de  med.,  1880. — Vulpian,  Sensibilite  des  lobes  du  cerveaii,  C.  B.  Ac.  sc,  1882. 

Ramoval  of  the  cortex — Degeneration. — Langley  et  Sheeeington,  Journ.  of  Phys., 
1884.  vol.  V,  p.  49.— Sheeeington,  Journ.  of  Phys.,  1889  et  1890.— Pitres,  C.  B.  Ac. 
sc,  1884. — Sanaeellt,  Processus  de  reparation,  Ajxh.  ital.  de  bioL,  t.  XIII,  p.  490. 

Reappearance  of  movements  after  destruction  of  the  cortex. — AELOiNG,'i?io/.,  1880. — 
GoLTZ,  Memoires  divers. — Feeeiee,  Les  fonctions  du  cerveau. — ViTZOU,  Arch,  de  Phys., 
1897. 

Reappearance  of  paralyses  under  the  influence  of  different  causes  (Aneniie,  anesthe- 
eiques). — R.  Teipiee. 

Post-anaesthesic  paralyses. — Veehogen,  Journ.  med.  de  Bruxelles,  1896. — Vautein, 
Congres  de  Nancy,  1876. 

Various  localizations  in  min. — Chaecot  et  Pitees,  Centre  du  relevem.  de  la  paupiere. 
Arch,  de  Bordeaux,  1894. — De  Bosco,  Relev.  paup.,  Bevue  de  neurol.,  1893  ;  II  Pisani, 
Gaz.  Sicula,  fasc.  I,  1893. — Beissaud,  Hemiplegie  faciale  particip.  de^  I'orbicul.,  Progres 
tned.,  1893. — Feee,  Tic  douloureux  de  la  face,  lesion  du  pli  courbe,  Biol.,  1876. — Gauche, 
Monoplegie  brachiale,  hemipl.  fac,  Biol.,  1879. — Hestee,  Ramoll.  pli  courbe,  ptosis 
gauche,  Journ.  of  nerv.  and  ment.  dis.,  1895. — Jopfeoy,  Monopl.  niembr.  inf.  ram.  lob. 
paracent.,  Arch.  Phys.,  1887. — R.  Teipiee,  Lesion  rolandic^ue  gauche,  hemiplegie  droite, 
conservation  mouv.  de  la  face,  Soc  sc.  med.  Lyon.  1865. 

Various  localizations  in  animals. — Beevor  et  Hoesley,  Arch,  de  neurol.,  Biol., 
1887. — Rethi,  IMastic.  deglutition,  Wien.  med.  Presse,  1894. — Richet,  Reflexe  de  direc- 
tion de  I'oreille,  Biol.,  1886. — Sheeeigton,  Centre  du  povxce  ;  centre  de  I'anus,  Congres 
de  Liege,  1892.— Vitzou,  Centre  visual  du  chien,  C.  B.  Ac.  sc,  1888,  t.  CVII,p.  279.— 
Weenee,  jMouv.  tronc  et  nuc^.  chien,  Allg.  Zeitsch.  f.  Psych.,  1895. 

Centres  of  phonation  ;  of  the  larynx. — Beoeckaert,  6e  Congres  otolaryngolog .  beige, 
1895. — Charcot  et  Pitres,  Arch.  clin.  de  Bordeaux,  1894. — Keause,  Arch.  f.  An.  und 
Phys.,  1884  ;  Brit.  med.  Journ.,  1889. — G.  M.arini,  Beal.  Acad.  med.  chir.  d.  Genova, 
1893,  analyse  par  Gaeel,  Province  med.,  1894. — Onodi,  Berlin,  klin.  Wochensch.  1894. 
— Semon  et  Hoesley,  Brit.  med.  Journ.,  1889,  I. 

Pseudo-bulbar  paralysis. — Hallipee,  These  Paris,  1894. 

The  brain  and  nutrition — Temperature  of  the  brain. — IMieto,  Aixh.  ital.  de  biol.,  1899, 
t.  XXXII,  p.  335. — ]\Iosso,  Crownian  Lectures  ;  Arch.  ital.  de  biol.,  1893,  t.  XVIII, 
p.  277,  et  1895,  t.  XXII,  p.  264. 

Cerebral  circulation. — Bayliss,  L.  Hill  et  Lowell  Gtjllaed,  Press,  intr.  cran.  cii-- 
cul.,  Journ.  of  Phys.,  1895,  vol.  XVIII,  p.  334. — Cavazzani,  Circul.  collat..  Arch.  ital. 
de  biol,  1891,  t.  XVI  ;  Action  de  I'asphyxie,  Ibid.,  1893,  t.  XVIII,  p.  54.— Dtjeet, 
Etude  anatom..  Arch.  Phys.,  1874. — L.  Hill  et  Macleod  .  .  .  Supposed  vasomot.  .  ., 
Journ.  of  Phys.,  1901,  p.  394. — Roy  et  Sherrington,  Regulat.  circul.  cerebr.,  Journ. 
of  Phi/s.,  1890,  p.  85. — RuMMO  et  Ferrannini,  Circ.  cer.  chez  I'liomme,  Arch.  ital.  de 
biol,  1889,  t.  XI,  p.  272. 

Influence  of  the  brain  on  the  circulation. — Binet  et  Vaschide,  Pression  du  sang  chez 
I'homme,  C.  B.  Ar.  sc,  1897,  t.  CXXIV,  p.  44. — Mosso,  Memoires  divers. — Thanoffer, 
Arch.  V.  Pfluger,  1879,  t,XIX,  p.  254. 

Influence  on  heat. — Voy.  Chaleur  animale. 

Influence  on  organic  life.— Bechterew,  Pupille,  Arch.  f.  An.  tind  Phys.,  1900. — 
Bechteeew  et  Mislawsky,  A7xh.  f.  An.  und  Phys.,  1889,  sup.,  1891,  p.  380. — P.  Bert, 
Coloration  de  I'axolotl,  Biol,  1879,  p.  65. — Bochefontaine,  Arch.  Phys.,  1876. 
CouTY,  Arch.  Phys.,  1876.— Judee.  Sahvat.,  C.  B.  Ac  sc,  1887,  t.  CV,  p.  893.— Herl. 
Parsons,  Dil.  pupille,  Journ.  of  Phys.,  1901. 

Disturbances  in  the  exchanges. — -Belmondo,  Echange  azote.  Arch.  ital.  de  biol, 
XXV,  3,  481.— D.  France,  Arch.  f.  An.  und  Phys.,  1900,  p.  209.— L.  Hill  etXABARRO, 
Ech.  des  gaz,  Journ.  of  Phys.,  1895,  vol.  XVIII,  p.  218. — Stcherbach,  Ech.  ac.  phos- 
phoriq..  Arch.  med.  cvp.,  1893,  Xo.  3. 

Trophic  disturbances. — Joffeoy  ...  a  la  suite  lesion  lobe  occipital,  Biol,  1875, 
p.  399. — Langlois  et  Richet,  Troubles  trophiq.  bilateraux  apres  lesion  de  I'ecorce 
ct^rebrale,  Biol,  1890,  p.  315.  ^ 


SECOND  SECTION 

Special   Innervations 

If  we  take  as  a  foundation  either  the  different  sensations  which  are 
aroused  in  us  by  external  provocations,  these  also  differing  in  their 
nature  and  mode  of  action,  or  the  motor  phenomena  which  are  most 
directly  associated  with  these  sensations,  we  may  divide  innervation 
into  five  great  systematizations,  or  principal  categories,  which  will 
be  visual  innervation  ;  auditory  innervation  ;  tactile  innervation  ; 
olfactory  innervation  ;   gustatory  innervation. 

Sensation  is,  in  fact,  the  quality  which  is  most  characteristic  of  the 
nervous  system  ;  this  latter  being,  of  all  the  tissues,  that  which  dis- 
plays it  in  the  highest  degree,  and  which,  on  account  of  its  complexity 
and  its  organization,  confers  on  it  its  highest  value.  This  first  con- 
ception is  a  matter  of  ordinary  knowledge.  On  the  other  hand,  all 
sensation  is  intimately  connected  with  motor  actions,  which  may 
effect  areas  of  the  nervous  systems  at  the  same  time  various  and  dis- 
tant, but  of  which  some  are  immediately  dependent  on  these  sensations,, 
and,  as  such,  are  characteristic  of  them.  Each  sensory  system  is  a 
sensitivo-motor  apparatus,  which,  in  a  certain  measure,  is  not  isolated 
from  the  others,  but  capable  of  being  so  isolated  ;  that  is  to  say,  is 
complete  in  itself.  Functional  links  exist  between  these  partial  systems, 
so  as  to  ensure  the  unity  of  the  nervous  system,  and  by  it  the  unity  of 
the  living  being.  This  second  conception,  which  sanctions  the  intimate 
connexion  between  sensation  and  motion,  has  begun  to  be  generally 
adopted.  Finally,  sensation  allows  of  an  infinity  of  degrees  and  of 
gradations  from  those  which  have  their  fullest  expansion  in  the  superior 
senses,  down  to  those  quite  obscure  ones  which  interpret  our  most 
elementary  requirements.  In  writing  a  complete  history  of  the  nervous 
system  it  becomes  necessary  to  connect  these  subconscious  (sometimes 
called  unconscious)  sensations  with  the  motor  acts  related  to  them,  to 
the  distinct  sensations  of  the  superior  senses,  according  to  their  func- 
tional affinities.  This  idea  of  an  obscure  consciousness  governing  all 
living  actions,  even  those  which  appear  quite  mechanical  and  auto- 
matic, is  the  most  modern  of  all  those  we  have  passed  in  review,  and 
daily  gains  more  adherents. 


488  SPECIAL    INNERVATIONS 

Specific  activities. — The  nervous  system  is  an  assemblage  of  partial 
systems,  each,  in  an  isolated  manner,  presiding  over  some  function  of 
a  determinate  nature.  None  of  these  can  replace  any  of  the  others, 
or  be  replaced  by  them.  This  partition  stands  out  very  clearly  when 
the  nervous  system  is  considered  at  its  periphery,  either  at  the  point 
of  arrival  or  of  departure  of  the  stimuli  by  which  it  is  traversed  :  it 
becomes  more  and  more  obscure  in  proportion  as  we  penetrate  the 
depths  of  the  system  ;  of  this  statement  the  question  of  cerebral 
localizations  is  a  proof.  We  shall  then  start  from  the  extremities  of 
the  nerves,  ascending  nearer  and  nearer  to  the  brain,  tracing  in  this 
way,  according  to  their  kind,  the  great  divisions  and  subdivisions  of 
the  nervous  functions.  The  sensory  field  is  particularly  favourable 
for  the  determination  of  this  kind  of  division. 

1.  Sensory  field  ;  its  divisions. — The  sensory  field  is  divisible  at  the 
periphery  into  five  parts,  corresponding  to  the  five  senses.  Each 
sense  is  adapted  to  a  particular  sort  of  stimulation,  we  may  even  say 
to  an  exciting  medium  of  a  special  nature,  to  a  specific  excitant 
which  cannot  be  replaced  by  that  of  another  sense.  Out  of  the  in- 
finitely varied  movements  by  which  it  is  surrounded,  our  organization 
has  chosen  five  particular  orders  :  these  are  the  source  of  all  our 
knowledge. 

The  retina,  or  sensitive  membrane  of  the  eye,  obeys  the  vibrations  of  the  ether, 
that  body  which  penetrates  all  others,  and  is  distinguished  from  them  by  its 
imponderable  nature. 

The  internal  ear  is  sensitive  to  the  vibration  of  sonorous  bodies,  and,  above  all, 
of  the  air,  another  elastic  medium,  eminently  suitable  for  the  propagation  of  an 
undulatory  movement  to  a  distance. 

It  must  be  observed  that,  among  the  undulatory  movements  of  the  air,  as  of 
the  ether,  our  organization  is  not  restricted  to,  or  has  not  succeeded  in  adai^ting 
itself,  to  all,  but  only  to  a  small  number  amongst  them,  to  those  for  the  ear,  which 
are  comprised  between  32  and  50,000  vibrations  in  the  second,  about  eleven 
octaves  ;  to  those  for  the  eye  which  are  comprised  between  450  to  880  trillions  of 
vibrations  the  second.  But  as  these  media  are  traversed  in  all  directions  by 
vibrations  of  every  length  which  co-exist  and  are  superposed  without  being  con- 
fovmded,  this  restriction  does  not  imply  any  diflficulty  or  real  gap  in  the  exercise 
of  the  senses. 

The  organs  of  taste  and  smell  are  affected  by  excitants  whose  physical  nature, 
modality  and  medium  of  propagation  are  absolutely  unknown  to  us,  but  which 
it  is  possible  to  conceive  of  as  being  also  vibratory  changes  of  a  special  natiu'e. 

The  skin,  which  is  the  organ  of  touch,  is  affected  by  the  contact  of  more  or  less 
resisting  bodies,  and  also  by  those  undulatory  movements  to  which  we  give  the 
name  of  heat.  In  this  sense,  which  is  less  specialized  than  the  others,  all  ordinary 
excitations  are  included,  such  as  tensions,  compressions  and  modifications  of 
whatever  nature  which  affect  ovir  superficial  or  deep  organs  and  belong  to  the 
sensibility  called  general. 

2.  Specificity  of  the  stimulus. — Each  of  these  excitants  is  sjjecific. 


SPECIAL    INNERVATIONS  489 

Excitation  is  a  shock,  a  communicated  movement  ;  we  learn  from 
physics  that  a  vibratory  movement  is  not  communicated  from  one 
body  to  the  other,  unless  resonance  exists,  that  is  to  say,  an  agreement 
between  the  vibrations  of  these  two  bodies.  The  organs  of  the  senses 
are  essentially  resonators,  the  word  being  taken  in  its  most  general 
sense.  The  retina  and  the  ear  are  alike  irresponsive  to  any  shocks 
except  those  which,  both  as  regards  quality  and  amplitude,  are  appro- 
priate to  them. 

Adaptation  of  the  senses  to  their  specific  excitants  ;  appropriated 
resonators. — Being  a  portion  of  the  ectoderm  which  is  developed  with 
a,  view  to  the  performance  of  special  functions,  each  organ  of  the  senses 
is  provided  with  a  special  resonator.  The  shock  of  the  external  medium, 
when  it  transgresses  certain  Hmits,  is  non-existent  for  the  resonator  ; 
but  when  it  possesses  the  right  tonality,  it  finds  a  gate  of  entrance  in 
this  sense  and  penetrates  the  nervous  system,  where  it  finds  itself  in 
■conflict  with  a  crowd  of  others,  and,  remaining  there  a  longer  or  shorter 
period,  leaves  it  in  the  condition  of  a  motor  phenomenon. 

But,  before  leaving,  it  gives  rise  in  the  depths  of  the  nervous  system, 
to  a  fact  which  we  call  psychical,  or  one  of  sensibility,  in  one  word,  to 
sensation,  in  opposition  to  the  physical  fact  of  impression. 

3.  Specific  nature  of  the  sensation. — We  have  said  that  impressions 
are  specific,  and  we  may  add  that  sensations  are  also  specific,  for  to  each 
particular  modahty  of  impression  a  particular  modahty  of  sensation 
corresponds.  Before  ending  in  the  deepest  part  of  our  being,  in  the 
most  abstract  notion  of  general  ideas,  which  has  the  conflict  of  sensa- 
tions for  its  origin,  these  latter  put  to  port  somewhere  in  the  nervous 
system  ;  there  is  therefore  a  functional  partition  of  sensations,  as 
there  is  one  of  impressions. 

Sensation,  a  fact  of  purely  internal  observation,  can  only  be  defined 
by  its  contrast  with  the  psychical  fact  of  impression.  It  is  not  in  the 
very  least  a  geometrical  representation  of  the  physical  changes  which 
give  birth  to  it.  The  ignorant  person  who  can  distinguish  between  a 
sound  and  a  colour  has  not  the  least  conception  of  a  sonorous  or 
luminous  vibration  ;  the  educated  man  alone  is  acquainted  with 
this  detail,  or  believes  that  he  can  explain  it. 

Sensation  results  from  an  association  of  stirnuli.  It  is  a  synthesis  of 
these  stimuli  effected  in  the  nervous  system. 

Uniformity  of  function  of  the  nervous  elements.— Further,  we  may 
add  that  a  shock  of  a  particular  sort  which  has  arisen  in  a  sensitive 
or  sensory  resonator  is  never  transmitted  to  the  brain  by  the  sensitive 
or  sensory  nerves,  retaining  its  original  character.  All  these  shocks, 
specific  in  their  origin,  are  brought  back  to  a  single,  or  at  any  rate  to 


490  SPECIAL    INNERVATIONS 

almost  an  uniform  state,  the  nerve  wave,  as  soon  as  they  enter  the 
nervous  system  properly  so  called.  The  nerve  wave  (with  some 
trifling  differences)  appears  to  be  of  the  same  general  form,  or,  in  a 
word,  of  the  same  nature,  in  all  nerves  (sensory,  sensorial  or  motor). 
Each  neuron,  taken  by  itself,  is  functionally  equivalent  to  any  other 
neuron  ;  there  are  not  any  specific  neurons,  properly  so  called. 

Specificity  of  the  neurons. — The  data  furnished  by  morphology  and  exiseriment 
have  so  far  pointed  to  the  predominance  of  fundamental  resemblances  between 
nerve  elements,  rather  than  to  real  differences  between  them,  except  as  regards 
those  wliich  are  contingent  and  without  known  relation  with  the  ftmction  of 
these  elements.  There  must,  however,  exist  between  one  and  the  other,  certain 
quantitative  or  qualitative  modifications,  in  order  that  these  elements,  by  being 
associated,  should  be  able  to  form  functionally  differentiated  systems.  These 
modifications  may  bear  only  on  characters  which  are  but  little  obvious  and  be 
themselves  individually  very  unimportant.  The  multiplicity  and  the  com- 
plexity of  the  associations  are  sufficient  to  enlarge  them  and  to  elicit  from  them 
very  dissimilar  effects.  On  the  other  hand,  these  modifications  may  be  confined 
to  certain  parts  of  the  neiu"ons,  for  example,  to  their  extremities  in  the  areas  by 
means  of  which  they  become  associated  the  one  with  the  other.  In  fact,  more 
notable  and  more  significant  differences  are  discoverable  in  their  polar  fields  than 
in  their  axons  or  their  cell  bodies. 

Further,  we  are  ill  equipped  for  the  struggle  required  in  order  to  seek  for  and 
understand  these  differences.  The  nerve  wave,  of  which  so  much  is  heard,  is 
almost  unknown  to  us  as  regards  its  real  form.  Some  facts  about  its  rate  of 
progress  are  all  that  we  possess. 

Experimentally,  our  ideas  on  this  point  are  based  on  the  two  following  facts  : 

(1)  The  nerve  fibre,  which  is  a  continuation  of  a  sensory  apparatus,  is  generally  re- 
fractory to  the  specific  excitant  of  this  sense.  From  this  it  follows  that  the  sensorial 
apparatus  is  both  a  resonator  adapted  to  the  external  excitant,  and  a  trans- 
foriner  of  the  excitation  which  adapts  it,  in  its  turn,  to  the  nerve  which  follows  it. 

(2)  All  the  nerve  fibres,  to  whatever  sense  (iunction)  they  may  belong,  are  capable  of 
receiving  certain  excitations  different  from  the  specific  ones,  and  which,  for  this 
reason,  are  called  ordinary,  or  general  stimulations  (pinching,  chemical  action, 
electricity,  etc.).  Whence  it  follows  that  these  fibres,  having  received  this- 
ordinary  excitation,  develop  a  specific  sensation  in  the  system  to  which  they 
belong. 

It  is  obvious  that  the  optic  nerve  is  not  a  channel  for  light,  nor  the  acoustic 
nerve  for  sound.  But  the  component  elements  of  each  of  these  two  nerves  have 
not,  as  regards  structure  or  properties,  anything  which  distinguishes  the  one  from 
the  other,  or  from  all  the  other  nerve  elements.  They  possess  the  common 
excitability  of  the  latter,  but  nothing  else.  The  Imninous  ray  appropriate  for 
the  stimulation  of  the  retina  has  no  effect  if  immediately  thrown  on  the  optic 
nerve  ;  the  sonorous  wave  is  without  effect  on  the  acoustic  nerve  ;  and  this 
because  the  adaptive  apparatus  is  lacking  in  both  cases.  But,  on  the  other 
hand,  ordinary,  commonplace  excitations  of  the  nervous  system,  such  as  pressure, 
pinching,  electrization,  excite  these  just  as  all  other  nerves,  and  so  give  rise  to- 
specific  sensations  corresponding  to  the  specific  excitant  of  the  senses  to  which 
they  belong. 

Examples. — Pressure  on  the  trunk  of  the  optic  nerve  gives  rise  to  a  luminous 
sensation.  In  the  operation  of  enucleation  of  the  eyeball  the  patient  perceives 
flashes  of  light,  resembling  lightning  (Tortual)  ;  only,  however,  on  the  condition 
that  the  fibres  of  the  optic  nerve  have  not  undergone  atrophy.     A  slight  pressure 


SPECIAL    INNERVATIONS  491 

on  the  ball  of  the  eye  towards  the  edge  of  the  retina  causes  the  apjiearance  of  a 
subjective  image  of  the  body  compressing  it  ;  this  is  what  is  known  as  a  pJios- 
phene.  By  turning  the  eye  firmly  downwards  under  the  closed  eyelids  and 
lightly  sliding  the  tip  of  the  first  finger  under  the  orbital  arch,  across  the  upper 
eyelid,  a  j)hosphene  is  created  which  is  perceptible  at  the  lower  part. 

Sliocks  brought  to  bear  on  the  temporal  bone  may,  at  the  same  time,  excite 
the  acoustic  nerve  in  a  mechanical  manner,  and  create  a  sonorous  sensation. 

Electrical  stimulation  applied  to  the  different  sensory  nerves  may  also  give  rise 
to  the  sensation  proper  to  each  of  the  senses  to  which  they  belong.  In  a  word, 
excitants  which  have  nothing  specific  about  them,  general  excitants,  that  is  to 
say,  those  capable  of  affecting  all  the  nerves,  create  specific  sensations  when  they 
can  find  the  entrance  to  special  systems  corresponding  to  the  different  senses. 

Definite  relation  between  impression  and  sensation. — Sensation  with 
its  specific  characters  may  then  exist  in  us  in  the  absence  of  the  particular 
excitayit  tvith  ivhich  it  ivas  originally  connected.  This  is  proved,  not  only 
by  the  preceding  analysis,  where  an  ordinary  excitant  is  seen  to  pene- 
trate artificially  into  one  of  our  sensorial  systems,  but  also  in  a  very 
simple  manner  by  the  fact  that  sensation  is  preserved  in  us  in  a  state 
of  residue  or  of  remembrance  after  the  external  excitant  has  disappeared. 
Indeed,  this  fact  of  conservation  implies  that  sensation  has  means 
appropriate  to  the  nervous  system  of  being  created  quite  independently 
of  the  presence  of  the  habitual  excitant.  According  to  the  statement 
of  J.  Miiller,  what  we  feel  is,  the  state  of  our  nerves.  We  can  feel  nothing 
outside  of  us  except  by  this  state  of  our  nerves,  and  we  can  continue 
to  feel  this  state  after  the  cause  by  which  it  has  been  elicited  has  either 
ceased,  lost  its  specific  value,  or  been  replaced  by  an  ordinary  cause. 

There  are  within  us  sensorial  systems  which  react  specifically  to 
every  stimulus  which  reaches  them.  These  systems,  at  their  surface 
of  contact  with  the  exterior,  are  furnished  with  special  apparatus 
(organs  of  the  senses)  which  select,  from  the  excitatory  shocks  of  every 
form  and  origin  by  which  we  are  surrounded,  those  which  can  in  an 
isolated  manner  penetrate  into  each  of  these  systems  to  the  exclusion 
of  the  others.  Thus  is  created  for  us  a  determinate  relation  between 
each  order  of  sensation  and  the  external  excitant  from  which  it  origin- 
ally arose.  This  relation  is  an  empirical  one,  but  is  sufficient  for  the 
daily  requirements  of  existence  ;  it  teaches  us  all  that  is  necessary  for 
us  to  know,  but  not  concerning  everything  external  to  ourselves.  By 
the  comparison  of  the  information  furnished  by  the  different  senses, 
these  indications  being  subjected  to  verification  and  criticism,  we  are 
in  a  position  to  make  a  distinction  between  our  actual  and  our 
reawakened  sensations  or  remembrances  ;  we  also  make  the  same 
distinction  between  the  normal  and  regular  external  sensation  and 
that  which  is  artificial  and  irregular.  When  this  criticism  is  wanting, 
there  is  hallucination. 


492  SPECIAL    INNERVATIONS 

Sensation  is  a  phenomenon  of  evolution  ;  it  is  at  the  same  time  both 
a  process  and  a  progress  ;  it  takes  place  in  a  system  composed  of  suc- 
cessive and  at  the  same  time  parallel  elements,  which  are  associated 
according  to  relations  special  to  it  and  of  a  very  complicated  order. 
In  the  same  way  as  the  system  which  acts  as  its  support,  it  is  formed 
of  numerous  elements  which  are  none  other  than  the  particular  activi- 
ties and  the  states  of  excitation  of  the  parts  composing  this  system, 
co-ordinated  according  to  a  law  which  is  special  to  it.  We  have  said 
that  the  stimulus  invades  the  system  and  advances  therein  in  the 
fashion  of  a  wave,  whose  form  becomes  more  and  more  complicated 
in  proportion  as  it  approaches  and  reaches  the  cerebral  cortex.  In 
this  forward  march  of  the  impulse,  where  is  the  precise  locality  of 
sensation  ?  Has  it  an  exclusive  and  defined  habitation  ?  What 
parts  are  sufficient  for  or  necessary  to  it  ?  What  does  experiment 
tell  us  on  this  subject  ?  How  are  the  facts  which  it  has  displayed 
to  us  to  be  interpreted  ? 


An  effort  has  always  been  made  to  arrange  the  recognized  facts  concerning  the 
structure  of  the  nervous  system  in  accordance  with  the  information  furnished 
by  observation. 

Interpretations  have  necessarily  varied  according  to  the  state  of  our  know- 
ledge on  these  points,  and  also  with  the  general  theories  obtaining  in  biology. 

Former  scheme. — The  three  data  essential  to  observation  are  :  (a)  the  specific 
nature  of  the  impression,  implying  a  specificity  of  the  receptive  organ  of  the 
senses  :  (6)  uniformity  of  function  of  the  nerve  fibres,  contrasting  with  the  speci- 
ficity of  the  receptive  element  :  (c)  specific  nature  of  the  internal  phenomenon 
of  sensation,  contrasting  in  its  txu"n  with  the  uniformity  of  the  transmitting  ele- 
ments. With  regard  to  these  data,  the  following  anatomical  scheme  was  quite 
recently  accepted  as  summing  up  the  structiu-e  of  the  nervous  system,  namely  : 
(a)  a  peripheral  cell  adapted  specifically  to  the  excitant  of  each  given  sense  ; 
(6)  a  fibre,  possessing  the  activity  common  to  all  fibres,  transmitting  the  impres- 
sion received  from  its  origin  to  its  termination  ;  (c)  a  central  cell  with  a  specific 
function,  realizing  the  internal  phenomenon  of  the  sensation. 

As  will  be  obvious,  this  scheme  distinguished  the  existence  of  two  kinds  of 
elements  in  the  nervous  system :  the  fibres  and  the  cells.  Uniformity  was 
allotted  to  the  first  of  them,  and  specificity  to  the  second.  This  specificity 
was,  in  its  turn,  again  divided  into  two  kinds  :  physical  specificity,  appertaining 
to  the  peripheral  cell  (adaptations  to  a  shock  of  a  determinate  natvire),  psychical 
specificity  to  the  central  cell  (sensation  of  a  determinate  nature). 

Thus  sensation  was  considered  to  be  a  cellular  function,  like  impression  itself, 
and  transmission  a  function  of  the  fibre,  which  was  thought  to  be  an  element 
distinct  from  the  cell. 

Its  insufficiency. — This  theory  crumbled  away  with  the  anatomical  thesis 
which  served  it  as  a  support.  We  no  longer  admit  the  existence  of  two  nerve 
elements  (the  cell  and  the  fibre),  but  only  of  one  (the  neiu-on,  which  is  a  cell  pro- 
vided with  fibrillary  poles).  The  division  between  nerve  elements  is  not,  as  was 
formerly  supposed,  between  the  cell  and  the  fibre,  but  between  the  terminal  and 
initial  ramifications  of  the  neurons.  The  jiathway  of  the  nerve  wave  giving  rise 
to  the  sensation  is  not  a  simple  fibre  stretched  between  two  cells,  one  peripheral 


SPECIAL    INNERVATIONS  493 

and  the  other  central  ;  but  is  formed  by  a  series  of  neurons  placed  end  to  end. 
The  junction  of  these  neurons  is  not  made  unit  by  vmit,  pole  by  pole,  but  by  a 
complicated  arrangement,  the  terminal  polar  field  of  each  antecedent  neuron 
according  with  the  initial  polar  fields  of  a  great  number  of  consecutive  neurons  ; 
and  reciprocally.  The  dividing  siu'face  which  outlines  the  locality  of  these  junc- 
tions is  not  simple,  but  enormously  twisted  and  complicated  ;  because,  in  addi- 
tion to  the  direct  contacts  between  neurons  of  great  length,  there  are  other 
indirect  ones  effected  between  neurons  of  short  or  medium  length  ;  thus  these 
associations  are  multiplied  to  an  infinite  degree.  Finally,  this  complication  of 
the  paths  followed  by  the  imj^vilse,  is  not  uniform,  but  increases  as  it  approaches 
the  cortex,  and  is  renewed  on  leaving  the  latter  in  order  to  gain  the  motor  organs. 
Of  the  former  theory  this  much,  however,  is  true,  namely,  that  the  physical 
specificity  of  the  impression  is  united  to  a  determinate  cellular  function  (organs 
of  the  senses)  ;  on  the  other  hand,  imder  a  slightly  altered  form,  we  retain  the 
conception  of  tuiiformity  in  tlie  function  of  neurites  (or  fibres  of  neurons).  But 
that  which  appears  to  be  destroyed  for  ever  is  tlie  conception  of  sensation  as 
being  a  cellular  function.  Sensation  is  a  systefnatic  function.  The  more  clear, 
conscious  and  refined  it  is,  so  much  the  more  complicated  and  highly  developed 
is  the  system  which  serves  as  its  support  and  lends  itself  to  its  evolution.  The 
proof  of  this  will  be  established  by  comparing  the  systems  in  which  reflex  sensi- 
bility is  observed  to  develop,  both  that  called  instinctiv^e  and  that  which  is  strictly 
conscious,  which  systems  define  the  three  principal  limits  of  the  gradation  of 
psychical  phenomena. 

Unity  of  the  sensation  ;  its  determinative  condition. — Sensation  is  a 
phenomenon  which  impresses  us  by  its  unity  ;  the  nervous  system  and 
the  component  systems  which  it  includes  are,  on  the  contrary,  dis- 
tinguished by  their  complexity.  Hence,  no  doubt,  arises  the  repug- 
nance which  has  been  felt  to  attaching  and  superposing  the  first  of  these 
to  the  second  ;  and,  by  a  logical  consequence,  the  converse  tendency 
to  imprison  sensation  in  the  smallest  known  biological  element,  namely, 
the  cell  (the  nerve  cell).  But  since  analysis  has  penetrated  this  so- 
called  element,  it  has  become  necessary  to  recognize  how  far  removed 
it  is  from  simplicity.  Unity  of  sensation  explained  by  unity  of  the 
cell  is  a  pure  delusion. 

For  ourselves,  our  nei'vous  system  is  one  and  indivisible  ;  this  is  because  we 
comprehend  it  with  our  internal  senses,  which  precisely  realize  its  analyses  or  its 
syntheses.  On  the  contrary,  the  nervous  system  of  one  of  our  fellow-creatures- 
appears  to  us  in  all  its  complexity  ;  this  is  because  we  grasp  it  with  our  external 
sense  which  is  cajDable  of  analysing  it.  In  the  first  case  the  nervous  system  is 
oirrselves,  that  is  to  say,  the  subject,  on  which  its  quality  of  sentient  being 
confers  its  unity.  In  the  second  case,  the  nervous  system  is  outside  ourselves, 
that  is  to  say,  an  object  which  we  can  divide  into  as  many  partial  beings  as  the 
power  of  our  means  of  analysis  loermits.  The  two  operations  employ  different 
and  in  no  way  superposable  modes  of  procedm-e.  The  internal  sense,  like  the 
external  senses,  proceeds  by  analysis  and  by  synthesis  ;  but  their  situation  in 
relation  to  each  other  is  such  that  the  one  often  builds  up  that  which  the  other 
analyses,  and  reciprocally.  An  absolute  harmony  between  the  two  would  cause 
all  the  practical  benefit  which  we  draw  from  the  arrangen^ient  to  be  lost. 

Seat  of  sensation. — If,  again,  we  represent  to  ourselves  the  impulse 


494  SPECIAL    INNERVATIONS 

advancing  in  the  nervous  system  after  leaving  an  organ  of  the  senses, 
we  ask  ourselves  at  what  point  of  its  journey,  at  what  precise  halting 
place  in  its  path,  does  it  become  a  sensation  ?  The  answer  usually  is  : 
in  the  cerebral  cortex.  The  brain's  cortex  is  not  an  ideal  surface,  but 
comprehends,  in  itself  alone,  complicated  systems  which  are  attached 
to  other  antecedent  and  consecutive  systems.  Experiment  points  out 
the  cerebral  cortex  as  being  a  locality  of  nervous  matter  possessing 
essential  functions  as  regards  the  development  of  sensation.  From 
this  point  of  view  the  analyses  which  are  carried  out  by  mutilations  of 
the  two  extremities,  or,  still  better,  of  the  roots  (organs  of  the  senses) 
and  the  summit  of  the  nervous  system  (cerebral  cortex)  are  very 
instructive. 

If  we  assume  that  an  organ  of  oixr  senses  is  suppressed,  impression  and  stimula- 
tion cannot  in  the  future  be  renewed  (exce^jt  in  a  very  incomplete  and  artificial 
manner)  ;  but  observation  teaches  us  that  they  still  joersist  in  us,  though  more 
or  less  weakened  and  in  an  indefinite  manner  (the  blind  person  sees  in  himself 
forms  and  colours,  remembrances  of  his  former  impressions,  etc.). 

If  we  imagine  the  cortical  area  corresponding  to  one  of  our  senses  obliterated, 
impressions  would  continue  to  flow  in  upon  us  with  the  same  abundance  and 
the  same  intensity  as  before,  but  clear  sensation,  conscious  and  personal  sensa- 
tion, would  be  lacking.  Has  this  fact  caused  the  total  disappearance  of  all 
possibility  of  sensation  ?  This  was  for  a  long  time  held  to  be  the  case,  and  this 
belief  was  founded  on  the  extraordinary  diminution  of  psychical  phenomena 
resulting  from  extremely  superficial  mutilations  of  the  brain.  But  it  must  be 
recognized  that  the  destruction  of  the  cortex  allows  an  instinctive  consciousness 
to  subsist  which  is  j^resided  over  by  the  inferior  regions  of  the  brain,  just  as  the 
destruction  of  these  regions,  in  its  turn,  allows  of  the  subsistence  of  a  reflex 
activity  which  in  itself  is  a  weakened  instinct,  or  the  rough  sketch  of  an  instinct. 
The  law  of  continuity,  which  has  nowhere  so  many  applications  as  in  the  living 
being,  is  here  clearly  displayed.  The  development  of  sensation  has  roots  deep 
down  in  the  inmost  structures  of  the  nervous  system.  Of  whatever  nature  it 
may  be,  and  in  whatever  degree  we  consider  it,  sensation  does  not  arise  all  at 
once,  in  an  abrupt  manner,  amongst  the  particular  elements  belonging  to  an 
exclusive  area  of  this  system  ;  but  it  is  being  prepared  during  the  whole  length 
of  the  patiis  which  it  traverses,  is  progressively  developed  in  its  course,  and  is 
finally  completed  on  arriving  at  its  summit.  Each  element  invaded  by  the  im- 
pulse adds  its  contingent  of  activity  in  a  determinate  order  to  this  organization, 
which  progressively  increases,  and  which,  when  realized,  is  sensation. 

Sensation  considered  with  regard  to  time. — Considered  with  regard 
to  space,  sensation  was  formerly  supposed  to  occupy  only  an  exclusive 
and  restricted  position  in  the  nervous  paths  which  are  traversed  by 
the  impulse.  We  now  give  it  a  wider  extension  by  assigning  to  it  a 
preparation,  a  development  and  a  completion.  Considered  with 
regard  to  time,  it  has  equally,  from  the  very  fact  of  the  progression  of 
the  impulse  through  the  nerve  paths,  a  limited  duration  ;  but  from 
this  point  of  view  a  distinction  must  be  made  between  the  strong  or 


SPECIAL    INNERVATIONS 


495 


victual  sensation,  and  the  remembrance  or  re-awakened  sensation,  whose 
intensity  is  feebler. 

Data  yielded  by  experiment  show  that  the  strong  sensation  exceeds 
in  duration  the  impression  which  has  given  it  birth  (example  :  the 
persistence  of  retinal  impressions,  or,  to  put  it  better,  of  optic  sensa- 
tion). Tliis  fact  ,  . 
is  in  harmony  1  V  Inr\  r^ 
with  the  theory 
of  the  develop- 
ment of  sensa- 
tion :  the  syn- 
thesis  of  its 
component  ele- 
ments being 
accompl  i  s  h  e  d 
during  the  pro- 
gression of  the 
impulse,  just  as 
happens  with 
regard  to  its 
time  of  exten- 
sion in  the  sys- 
tem. 

Specific  nature 
of  the  sensorial 
systems.  —  The 
sensation  c  o  r- 
responding  to 
each  sense  (vis- 
ual, auditory, 
tactile,  sensa- 
tions, etc.)  is 
developed  in  a 
particular  sys- 
tem retaining, 
up  to  a  certain 
point,  its  de- 
pendence   and 

its  distinct  limits.  Each  of  these  sensations  has  its  special  quali- 
ties, this  being  the  reason  why  it  is  called  specific  :  the  system  which 
gives  it  support  must  then  also  be  specific.  Like  the  sensations  them- 
selves, these  systems  display  in  their  constitution  features  common  to 


Fig.  '206. — General  arrangement  of  the  centripetal  paths  of  the 
different  senses  and  their  morphological  differences. 

Two  neurons  placed  ill  succession  ;  peripheral  neuron  (cell  in  black)  ; 
deep  neiu-on  (cell  in  white). 

A,  general  sensibility  ;  B,  taste  ;  C,  audition  ;  D,  olfaction  ;  E, 
vision. 

The  dotted  line  XSP  indicates  the  displacement  of  tlie  peripheral 
neurons  towards  the  periphery  starting  from  that  of  audition  (C). 

The  dotted  Une  CSG  marks  the  same  change  of  position  for  the  deep 
neurons  starting  from  that  of  olfaction  (D). 

AN,  nerve  axis  ;  DD,  decussation  of  the  axis  cyhnders  of  the  deep 
neurons. 


496  SPECIAL    INNERVATIONS 

all,  and.  should  at  the  same  time  present  particular  ones  from  which 
each  derives  its  specific  nature.  Only,  in  a  manner  contrary  to  that 
existing  for  sensations,  in  which  the  specific  characters  are  the  most 
obvious,  it  is  in  these  systems  the  points  of  resemblance  which  are 
easiest  of  recognition  ;  this  results  once  more  from  the  difficulties  of 
an  opposite  nature  which  are  encountered  by  analysis,  whether  it  be 
of  sensation  itseK  or  of  the  anatomical  system  in  which  its  evolution 
is  carried  out. 

The  visual,  auditory,  tactile,  olfactory  and  gustatory  systems  are 
constructed  of  the  same  elements,  the  neurons,  on  the  same  general 
morphological  plan  recognizable  in  each  of  them.  They  present,  it  is 
true,  markedly  obvious  differences  of  form,  but  these  external  and 
contingent  differences  do  not  explain  the  differences  of  their  function. 

The  functional  specificity  of  each  of  them  depends  in  all  probability 
on  the  particular  modality  of  the  relations  contracted  by  their  com- 
ponent elements,  as  well  as  by  the  primitive  systems  associated  by 
them. 

Motor  specificity. — At  the  terminal  extremity  of  the  nervous  system,  whence 
stimuh  proceed  to  produce  their  ultimate  effect,  we  find  peripheral  organs  formed 
of  cells  adapted  to  a  corresponding  motor  function.  These  organs  are  sub- 
divided into  two  large  groups,  each  of  which  discharges  an  important  function  ; 
(1)  Muscles  whose  f miction  is  above  all  energetic,  and  (2)  Glands  whose  function 
is  more  particularly  chemical,  that  is  to  say,  elaborative  of  particular  products. 
The  first  are  the  organs  of  a  movement  which  is  especially  massive  and  amplified  ; 
the  second  those  of  movement  more  particularly  molecular,  although  in  both 
these  two  orders  of  movement  are  represented. 

The  essential  function  of  the  one  is,  in  fact,  contraction,  that  of  the  other, 
secretion.  Both  one  and  the  other  of  these  two  functions,  especially  the  second, 
present  diverse  and  varied  modalities,  and  owing  to  this  fact  they  are  specific. 

By  the  help  of  the  muscles  and  of  the  glands,  the  excitatory  cycle,  after  having 
passed  through  the  phases  above  described,  terminates  in  acts  of  a  pre-eminently 
physical  nature.  Born  in  the  physical  world,  it  returns  thither  and  is  there  con- 
summated. These  final  actions,  taken  individually,  represent  cellular  fiinctions. 
But,  considered  in  their  relationship  with  others,  they  rej)resent  more  or  less 
complicated  co-ordinated  acts  ;  in  a  word,  systematic  acts  ;  this  co-ordination, 
or  systematization  still  being  the  work  of  the  nervous  system,  which  distributes 
the  impulse  to  these  motor  apparatus  in  a  determinate  order. 


CHAPTER    1 

TACTILE    INNERVATION 

Cyclic  system. — The  system  which  serves  as  a  basis  for  tactile  in- 
nervation, like  all  analogous  sensory  systems,  and  like  the  nervous 
system  in  its  entirety,  is  necessarily  a  cyclic  one,  which  receives  move- 
ment, transforms  it,  retains  it  as  long  as  it  chooses,  and  then  restores 


TACTILE    INNERVATION 


497 


it  to  the  medmm  from  which  it  first  received  it.  This  system  is  not 
invariable  in  its  hmits  and  its  direction,  but  its  connexions  with  other 
similar  systems  permit  of  its  borrowing  their  paths  of  return,  so  as  to 
increase  still  further  the  variety  of  the  motor  reactions.  However,  it 
is  possible  to  recognize  paths  of  reflexion  which  are  in  some  sort  natural 
and  habitual  to  it,  and  which,  after  making  the  reservations  mentioned 
above,  will  serve  to  round  off  its  description. 

Its  extension  to  the  deep  organs. — In  spite  of  these  restrictions,  it  is 
necessar}^  to  understand  that  the  system  thus  defined  is  graduated  as 
concerns  its  constituents,  Hke  the  sensibility  to  which  it  acts  as  a 
support.  Nothing  is  clearer  than  the  connexion  between  movement 
and  sensation  in  the  action  of  feeling  a  body  with  the  hand.  In  other 
areas  of  the  skin  the  help  of  the  muscles  is  no 
longer  the  same,  and  the  more  so  as  sensation 
is  there  less  acute.  In  the  deep  organs  sensi- 
bility is  still  more  obtuse,  although  it  is  still 
present  ;  and  hence,  this  weakened  sensibility 
is  little  know^n  to  us.  We  may  make  an  ex- 
ception as  regards  the  muscular  tissue,  in 
which  the  relations  between  sensation  and 
motion  once  more  become  evident  ;  but  in 
approaching  this  aspect  of  the  question  we 
enter  into  the  detail  of  the  function  instead 
of  considering  it  as  a  whole.  We  may,  to 
begin  with,  confine  our  study  to  that  of  touch 
properly  so  called,  and  to  the  motor  reactions 
by  which  it  is  directly  served. 

A.  Data  furnished  by  anatomy. — The 
organ  of  touch,  properly  so  called,  extends 
over  the  whole  surface  of  the  body  with  the 
skin,  which  contains, its  special  apparatus. 


Fig.  207. — Pacinian  corpus- 
cles of  the  middle 
finger  (after  Henle  and 
Kolliker). 


Cutaneous  covering. — These  apparatus,  which 
sometimes  go  by  the  name  of  teminations  of  sensory 
nerves,  are,  on  the  contrary,  their  origin,  if  we  consider 

these  nerves  no  longer  from  tlie  jaoint  of  view  of  their  development,  but  only  as 
paths  of  conduction.  They  differ  in  their  structure  and  their  situation.  In 
fact,  anatomists  distinguish  between  sub-dermic  apparatus,  intra-dermic  appa- 
ratus, and  intra-epidermic  nervous  ramifications,  to  which  is  commonly  conceded 
the  function  of  being  receptive  for  cutaneous  impressions. 

Sub-dermic  apparatus. — Corpuscles  of  Pacini  or  of  Vater. — These  are  ovoid 
bodies,  visible  to  the  naked  eye,  but  more  clearly  with  the  lens  (they  are  from 
1-5  millimetres  long),  divided  at  the  extremity  into  nervous  ramifications,  situ- 
ated in  the  subcutaneous  cellular  tissue.  They  are  formed  of  a  thick  covering 
made  up  of  a  series  of  very  regular  concentric  layers  (the  last  expansion  of  the 

P.  K  K 


498 


SPECIAL    INNERVATIONS 


slieatli  of  Henle).  A  nerve  fibre,  soon  despoiled  of  its  myelin,  and  reduced  to 
its  axis  cylinder,  penetrates  into  the  cavity,  traverses  its  long  axis,  afterwards 
displaying  several  short  ramifications  which  assume  the  shape  of  a  button.  Be- 
tween the  fibre  and  the  capsule  a  cellular  mass  is  interj^osed  (the  club)  formed  of 
special  cells. 

Distribution. — These  corpuscles  are  unequally  divided  according  to  the  cuta- 
neous areas.     Rauber  has  counted  on  one  half  of  the  body — 

On  the  shoulder 1-  On  the  hip 5 

On  the  forearm  and  the  arm  .       .      161  On  the  leg  and  the  thigh    .      .      .       138 

On  the  hand 414     ;      On  the  foot 275 

On  half  of  the  trunk 4G 

Total 1,051  for  half  of  tlie  cutaneous  surface. 

They  are  found  not  only  under  the  skin,  but  also  in  the  articulations,  the  bones 
and  the  mesentery. 

They  are  not  the  organs  of  touch,  but  those  of  a  more  general  function  of 
sensibility  than  that  we  call  tactile. 

Intra-dermic  apparatus. — Corpuscles  of  Meissner. — Much  smaller  than  the  pre- 
ceding, these  are  olive-shaped  and  are  deprived  of  tlie  thick  covering  possessed 
by  the  former.  The  nerve  fibre  which  penetrates  them,  instead  of  being  straight, 
makes  more  or  less  numerous  spiral  turns.  It  gives  off  axis-cylinder  ramifications 
deprived  of  myelin  towards  their  extremities,  which  in  this  corpuscle  are 
arranged  in  a  regular  manner.     This  corpuscle  is,  in  fact,  formed  of  special  cells. 


Fig.  208. — Pacinian     corpuscle     of      the 
mesentery  of  a  cat  (after  rrey).j 

a,  nerve  fibre  forming  its  pedicle  ;  b, 
system  of  lamellsB  or  concentric  capsules  ; 
cc,  central  cavity  where  the^axis  cylinder  is 
found. 


Fig.  209. — Papilla  of  the  skin  of  the  fore- 
finger with  a  touch  corpuscle  (after 
Ranvier). 

nn,  afferent  nerve  tube :  aa  glomeruli  witli 
their  tactile  discs  (prepared  by  the  chloride 
of  gold  method). 


which  may  be  called  specific,  since  they  transmit  the  impulse  to  the  polar  ramifi- 
cations of  the  sensory  nerve.  And  for  this  jjurpose  each  ramification  with  its 
swollen  or  flattened  extremity  is  included  in  the  interval  between  two  cells. 
Thus  the  number  of  these  cells  is  proportional  to  that  of  the  ramifications.  These 
corptiscles  are  simple  or  composite,  according  to  whether  the  fibre  ending  in 


TACTILE    INNERVATION 


499 


them  remains  simple  or  is  divided  for  the  pm-pose  of  distributing  its  ramifications 
to  several  superposed  formations. 

Distribution. — The  corpuscles  of  Meissner  have  a  much  more  restricted  and 
much  better  defined  localization  than  those  of  Pacini  ;  their  seat  is  in  the  hand 
and  the  foot,  specially  in  the  pulp  of  the  fingers  and  the  toes.  They  are  more 
closely  allied  than  are  the  preceding  to  the  function  of  touch  properly  so 
called. 

In  different  areas  endowed  with  a  fairly  large  amount  of  sensibility  may  be 
found  analogous  but  simpler  formations  ;  for  example  :  the  corpuscles  of  lirause, 
in  the  conjimctiva,  which  seem  to  be  a  rough  sketch  of  the  preceding  :  the  spiral 
twists  are  scarcely  indicated,  and  the  tactile  cells  are  reduced  to  a  very  small 
number — three  or  five. 

Intra-epidermic  ramifications. — 
The  epidermis  is  penetrated  by 
uncovered  arborizations,  springing 
from  the  network  of  the  nerves  of 
the  cutis  vera,  which  plunge  into  its 
thickness  and  penetrate  right  into 
the  cell  of  the  mucous  bodies  of 
Malpighi,  in  which  they  terminate. 
The  relations  of  the  cutaneous 
nerves  with  these  cells  (which  are 
of  an  epithelial  nature)  innnediately 
recall  those  of  these  same  nerves 
with  the  cells  of  the  glands  of  the 
skin  and  also  the  nervous  glandular 
terminations  in  general. 

Up  to  the  present  time  there  has 
been  no  hesitation  in  comparmg 
them  to  the  receptive  arborizations 
of  the  nerves  of  sensation  ;  and  this 
opinion  is  founded  on  the  belief  that 
the  epidermis,  in  which  no  aiapreci- 
able  movement  can  be  discerned, 
has  no  connexion  with  the  centri- 
fugal nerves.  This  purely  negative 
opinion  may  be  devoid  of  fomida- 
tion.  The  fact  of  the  penetration 
of  intra-epidermic  nervous  termina- 
tions into  the  protoplasm  of  the 
investing  cells  of  the  skin  would 
lead  us  to  suppose  that  the  nerve  conveys  the  impulse  to  these  cells  rather  than 
that  it  receives  it  from  them.  These  terminations  are  probably,  in  part,  those 
of  the  centrifugal  elements,  which  have  been  discovered  in  the  posterior  roots. 

Deep  organs. — Not  only  the  skin,  but  also  the  deeply  seated  organs,  the  mucous 
and  the  serous  membranes,  in  fact  all  the  organs  possess  sensory  nerves,  of  which 
the  initial  arborizations  insinuate  themselves  between  their  elements  or  com- 
ponent bundles.  The  mesentery  contains  corpuscles  of  Pacini  in  the  conjvmctive 
tissue  which  separates  its  sheets.  These  same  corpuscles  may  also  be  fovmd  in 
the  connective  tissue  which  borders  upon  the  articulations.  The  capillaries  dis- 
play terminations  which  are  supposed  to  have  a  sensory  function  (Ranvier),  The 
dura-mater  contains  nervous  ramifications  with  free  arborizations  (P.  Jacques). 
The  muscles  and  the  tendons  are  also  provided  with  sensory  receptive  organs,  of 
wliich  mention  will  be  made  when  alluding  to  the  muscular  sense.     This  is  an 


Fig.   210. — Tactile    corpuscles    of.   increasing 
complication  (after  M.  Duval). 

A,  corpuscle  of  Grandry  with  one  tactile  disc  DT, 
and  two  tactile  cells  CT  ;  B,  corpuscle  with  two 
discs  and  three  cells  ;  C,  corpuscle  of  Meissner  ; 
I,  2,  3,  its  components  (corpuscles  of  Grandry)  ; 
X,  nuclei  of  the  tactile  cells  ;  a,  nerve  fibre  ;  SI, 
interannular  segment. 


500 


SPECIAL    INNERVATIONS 


extension  to  most  organs  of  a  variety  of  sensation  analogous  to  that  of  the  skin, 
this  being  what  has  gained  for  it  the  name  of  general  sensation,  and  not  the 
demonstrably  incorrect  fact  that  it  is  an  element  common  to  all  other  sensibilities. 
It  is  of  a  special  nature,  but  its  anatomical  field  has  invaded  nearly  all  the  organ- 
ism, with  the  exception  of  some  restricted  areas. 


B.  Data  of  physiological  observation. — We  need  only  observe 
our  owTi  organization  to  be  convinced  that  impressions  received  by 
the  cutaneous  surface  arouse  in  us  sensations  of  varied  nature.  There 
are  generally  discerned  :  (1)  the  sensation  of  contact  (touch  properly 
so  called)  ;  (2)  the  sensation  of  temperature,  which  may  be  divided 
into  a  sensation  of  heat  and  a  sensation  of  cold  ;  (3)  the  sensation  of 
pain. 

This  distinction  is  especially  based  on  the  fact  that  each  of  these 
three  modalities  of  cutaneous  sensibility  may  disappear  in  an  isolated 
fashion,  allowing  of  the  persistence  of  the  other  two  ;  thus  arise  the 
three  varieties  of  sensory  cutaneous  paralysis,  ancesthesia  properly 
so  called,  thenno-ancesthesia  and  analgesia. 

The  problem  here 
laid  down  is  to  as- 
certain if  these 
three  very  distinct 
forms  of  cutaneous 
sensibilit,y  are, 
when  starting  from 
the  place  where  the 
reception  of  i  m- 
pulses  is  effected, 
united  to  special 
receptive  apparatus 
and  to  distinct  con- 


FiG.   211. — Various  intra-eiDithelial  terminations. 
A,  epithelixxm  of  the  larynx  (vocal  cords) ;  BC,  respiratory  region 
of  the  nasal    fossae  with  its  vibratile  epitheUuni,  in  the  rat. 


ductors,  or  if  their   modality  depends  on  distinct  conditions  of  the 
functional  activity  of  common  apparatus  and  conductors. 

1.  Nature  of  the  stimuli. — Starting  from  the  stimulus  itself,  we  see 
that  it  is  presented  under  two  forms  (and  not  three),  which  are  clearly 
distinct  :  first,  a  stimulus  of  a  mechanical  nature,  which  is  the  contact 
of  bodies  with  the  skin,  and  which  when  exaggerated  becomes  pressure  ; 
and  second,  a  stimulus  of  a  physical  nature,  heat,  which  we  compare, 
not  to  a  massive,  but  to  a  molecular  movement  of  warm  bodies.  Pain 
has  no  special  stimulus  ;  it  generally  arises  whenever  the  stimulus  acquires 
an  exaggerated  intensity,  which,  exceeding  the  usual  limits  of  the 
function  of  organs,  exerts  in  consequence  a  more  or  less  destructive 
action  on  these  organs. 


TACTILE    INNERVATION  501 

It  is  maintained  that  this  is  the  case  not  only  as  regards  the  skin, 
but  also  as  concerns  the  sensorial  apparatus  with  more  or  less  precision  : 
too  brilliant  a  light,  too  acute  or  too  shrill  a  noise  give  rise  to  a  dis- 
agreeable sensation,  which  is  pain  in  an  attenuated  form. 

Discussion. — This  first  distinction  being  n:iade,  we  may  inquire  if  the  specificity 
of  the  two  remaining  stimuh  is  connected  with  the  specificity  of  the  apparatus 
receiving  their  exciting  shocks.  In  organs  Hke  the  eye  or  the  ear,  the  question 
is  easily  answered,  because  the  specific  receptive  elements  are  distinct,  both  as 
regards  form  and  their  special  situation  in  the  interior  of  the  apparatus.  In  the 
skin,  supposing  that  such  elements  exist  there,  these  two  characters  would  be 
wanting  :  there  are  no  cutaneous  areas  especially  appropriated  for  the  reception 
of  thermic  impressions,  as  the  retina  is  in  the  eye  for  that  of  luminous  impressions, 
amongst  other  membranes  possessing  a  common  sensibility  :  and  although  we 
find  in  the  cutaneous  covering  as  many  as  three  orders  of  apparatus  receptive  of 
stimuli,  yet  we  have  no  reason  to  believe  that  any  of  them  is  specifically  con- 
nected with  the  sense  of  temperature.  As,  on  the  other  hand,  the  specificity  of 
thermic  sensation  is  evident,  we  find  oiu"selves  confronted  by  a  problem  the 
solution  of  which  requires  a  certain  amount  of  information  which  is  now  lack- 
ing. 

While  on  this  subject  it  may  be  added,  that  the  specific  receptive  element  of 
any  particular  sense  may  be  brought  into  play  by  stimuli  of  different  nature. 
The  retina,  for  instance,  is  specifically  excitable  by  the  ethereal  waves  which  we 
call  luminous,  but  it  is  so  also  bj^  mechanical  means,  the  phosphenes  being  a  proof 
of  this.  Spread  out  on  the  surface  of  the  skin  instead  of  being  sunk  behind  the 
refracting  media  of  the  eye,  the  retina  would  warn  vis  at  the  same  time  of  the 
contact  of  bodies  and  of  the  existence  of  luminous  waves.  It  is  true  that  it 
would  only  give  us  a  solitary  and  unique  impression  analogous  to  that  of  the 
phosphenes.  In  fact,  far  from  going  out  to  seek  mechanical  stimulation  from 
the  contact  of  bodies,  the  retina  is,  on  the  contrary,  protected  from  it  by  its  posi- 
tion located  deeply  behind  the  transparent  media,  which  only  allow  of  its  being 
reached  by  undulations  of  the  ether  ;  this  prevents  it  from  learning  how  to 
differentiate  between  the  two  stimuli.  If  these  conditions  were  altered,  it  might 
be  possible  for  it  to  become  capable  of  fvunishing  us  with  the  elements  of  the  two 
sensations.  It  is  necessary  to  seek  in  some  condition  of  this  nature  for  the 
capacity  of  the  skin  to  give  us  information  with  regard  to  excitations,  both 
thermic  and  mechanical. 

2.  Experimental  dissociation. — The  different  sensibilities  of  a  cutane- 
ous area  may  be  observed  to  be  dissociated  after  injuries  or  operations 
affecting  the  corresponding  sensory  nerve.  After  section  of  a  nerve 
trunk  it  has  been  found  that  the  thermic  and  painful  sensibilities  have 
been  lost,  while  tactile  sensibility  has  been  preserved  (Letievant,  Weir- 
Mitchell,  Richet,  Charcot,  etc.)  ;  or.  rather,  they  are  all  three  abohshed, 
but  the  area  of  thermic,  and  painful  insensibility  markedly  encroaches 
on  the  area  of  tactile  insensibility  (Cavazzani,  Manca).  This  dis- 
sociation is  called  syringomyelic,  because  it  is  observed  in  certain  affec- 
tions of  the  spinal  cord.  If  a  superficial  nerve  like  the  ulnar  is  com- 
pressed, the  different  sensibilities  will  also  be  seen  to  progressively 


502  SPECIAL    INNERVATIONS 

weaken  and  disappear  ;    the  thermic  and  that  of  pain  first,  while  the 
tactile  sense  is  relatively  preserved  (Biernacki). 

Facts  of  this  nature  seem,  at  first  sight,  favourable  to  the  existence  of  distinct 
conductors  for  these  different  modes  of  sensation.  At  the  same  time,  even  from 
tliis  simple  point  of  view,  the  difficulties  of  the  interjjretation  are  not  avoided, 
and  the  following  hypothesis  may  be  preferred  to  it.  Each  sensory  nerve  has 
its  area  of  distribution  in  the  skin,  but  these  areas  mutually  overlap.  The  per- 
sistence of  tactile  sensibility  after  section  of  a  nerve  trunk  may  be  explained 
by  the  fact  of  the  invasion  of  its  territory  by  the  fibres  of  the  neighbouring 
trunks.  The  weakening  or  abolition  of  thermic  and  painful  sensibility  may  be 
explained  by  the  insufficiency  of  this  collateral  innervation.  In  other  words, 
stimulation,  in  order  to  produce  pain  or  the  sensation  of  temperature,  must  affect 
more  fibres  in  the  same  point  than  it  is  necessary  for  it  to  do  in  order  to  produce 
the  sensation  of  contact. 

3.  Persistence  of  the  impression. — It  may  be  demonstrated  (both 
for  the  skin  and  the  retina)  that  the  impression  persists  a  certain  time 
after  the  removal  of  the  stimulus.  If,  by  the  aid  of  a  rotatory  mechan- 
ism, two  shocks  are  periodically  communicated  to  a  finger,  being 
repeated  on  the  average  at  ^^  o^  ^  second  interval,  these  two  impres- 
sions are  perceived  as  one.  If  the  two  successive  shocks  are  received 
by  two  symmetrical  fingers  on  the  two  hands,  the  result  is  the  same. 
This  is  a  proof  that  the  sensation  of  the  first  shock  still  lasts,  with  a 
practically  uniform  intensity,  until  the  arrival  of  the  second  impression. 
The  rate  of  the  shock  augments  the  persistency  of  the  sensation,  but  in 
a  feeble  manner. 

Estimation  of  the  rate  of  transmission  in  the  sensory  nerves. — On  this  fact  a 
method  of  measuring  the  rate  of  nervous  transmission  in  the  sensory  system  has 
been  founded.  If,  instead  of  receiving  the  two  shocks  on  two  symmetrical 
regions,  that  is  to  say,  on  two  regions  placed  at  the  same  distance  from  the  brain, 
the  second  shock  is  received  in  a  region  nearer  to  the  latter  :  for  example,  the 
hand  and  the  face,  a  fusion  of  the  sensations  results,  but  leaving  a  greater  interval 
than  when  the  two  symmetrical  regions  were  in  question.  The  difference  between 
the  two  intervals  ineasures  the  difference  of  duration  between  the  two  trans- 
missions. On  the  contrary,  if  the  shocks  are  received,  tlie  first  on  a  finger  and 
the  second  on  a  toe,  the  interval  in  order  to  obtain  fusion  must  be  diminished  by 
the  entire  quantity  representing  the  difference  of  duration  of  the  sensory  trans- 
missions from  the  foot  and  the  hand  respectively  up  to  the  sensorium.  Accord- 
ing to  these  experiments,  the  rate  of  transmission  is  greater  in  the  spinal  cord 
than  in  the  nerves  (Blocli). 

4.  Primitive  element  of  tactile  sensation. — According  to  Mendels- 
sohn, every  sensation  elicited  by  mechanical  irritation  of  the  skin 
may  be  reduced  to  a  sensation  of  pressure  :  if  this  is  not  the  only 
element  of  tactile  sensation,  it  is  at  any  rate  its  principal  element. 
The  sensation  of  pressure  varies  according  to  two  conditions,  two 
factors,  which  are,  first,  the  intensity  of  the  stimulus  or  weight  sup- 
ported, and  secondly,    the  extent  of  the  cutaneous  surface  submitted 


TACTILE    INNERVATION  503 

to  the  pressure.     By  varying  individually  either  one  or  the  other  of 
these  factors,  two  series  of  values  are  obtained. 

If,  on  an  equal  surface,  the  intensity  of  the  weight  is  varied,  the 
differential  perceptihility  of  the  direction  of  the  pressure  is  determined. 

If,  Avith  an  equal  intensity  of  stimulus  (mth  equal  weight),  the 
stimulated  surface  is  varied,  the  tactile  acuteness  is  determined.  This 
plays  as  regards  the  tactile  sense  the  same  part  that  visual  acuteness 
plays  in  that  of  vision. 

Differentiated  perceptibility  and  tactile  acuteness  are  necessarily 
closely  connected  with  each  other,  the  first  being  unable  to  operate 
without  the  second.  Nevertheless,  they  are  susceptible  of  undergoing 
independent,  but  not  parallel,  mutual  variations  when  cutaneous 
sensibility  varies  (according  to  the  area,  the  state  of  the  subject,  and 
lesions  of  the  nervous  system). 

5.  Stereognostic  sense. — -We  possess  the  faculty  of  appreciating  with 
the  eyes  shut  the  form  of  bodies  brought  into  contact  with  the  skin. 
This  appreciation  is,  however,  only  approximately  accurate  as  regards 
the  most  sensitive  surfaces,  the  palm  of  the  hand  for  instance  ;  it 
brings  two  factors  at  the  least  into  play,  namely,  on  the  one  hand 
the  tactile  sensibility  of  the  cutaneous  area  in  contact  with  the  object 
sought  to  be  recognized  ;  on  the  other  hand,  tlie  deep  sensibility  of 
the  parts  which  either  undergo  or  execute,  the  movements  of  the  hands 
and  jfingers  ensuring  their  contact  with  the  object.  A  portion  of  this 
sensibility  returns  to  the  muscles  w^hich  execute  these  movements, 
and  is  allied  to  the  so-called  muscular  sense. 

Thus  we  see  that,  when  the  sense  of  touch  is  exercised,  an  active 
element  intervenes  to  amplify  and  complete  the  information  provided 
to  us  by  this  sense,  whence  is  derived  the  name  active  touch  given  to 
it  under  these  circumstances. 

Stereognostic  sensation  is  a  complex  sensation. — It  is  formed  by  the 
association  of  simpler  sensations  and  is  developed  in  a  more  complex 
system  than  those  serving  alone  as  a  field  to  these  last-named. 

A.  PROJECTION  ON  THE  GREY  AXIS 
The  tactile  stimuli  received  in  the  cutaneous  nervous  apparatus  are 
projected  into  the  spinal  cord.  This  projection  is  effected  by  the 
paths  of  the  neurons  of  the  posterior  roots.  For  each  of  them  it  is 
merely  an  ordinary  and  isolated  fact  of  conduction.  But  it  is  remark- 
able that  even  from  its  origin,  that  is  to  say,  from  the  apparatus  recep- 
tive of  the  stimulus,  this  projection  implies  the  fact  of  association. 
We  know  that  each  sensory  root  has  a  determinate  cutaneous  area  ; 
but  we  also  know   that   these  areas  mutually  penetrate   to  such  an 


504 


SPECIAL    INNERVATIONS 


extent  indeed  that  the  area  of  a  given  root  is  covered  in  its  superior 
half  by  that  of  the  root  of  the  preceding  number,  and  in  its  inferior 
half  by  that  of  the  root  of  the  following  number.  An  area  of  the  skin 
of  such  small  extent  as  only  to  give  07ie  sensation  to  the  compass  of 
Weber,  in  reality  projects  the  stimulus  by  tivo  or  several  roots.  Unity 
of  sensation  is  in  no  way  incompatible,  as  is  obvious,  with  multiplicity 
of  conducting  tracts.  The  i7nimlse,  even  before  reaching  the  grey 
matter  of  the  spinal  cord,  falls  into  a  systematized  assemblage  which 
helps  to  diffuse  it  throughout  the  nervous  system. 

1.  Passage  through  the  spinal  ganglia. — The  ganglia  of  the  posterior 
roots  contain  the  cells  of  origin  of  the  neurons  of  projection  between 
the  skin  and  the  spinal  cord  (sensory  nerves),  cells  which  may  be  con- 
sidered as  being  placed  on  their  course  at  a  great  distance  from  their 
two  extremities.     These  cells  were  at  first  thought  to  be  mutually 

unconnected,  follow- 
ing the  example  of 
the  nerve  fi  b  r  e  s. 
Dogiel  has  since 
shown  that  they  are 
provided  with  pro- 
longations, by  means 
of  which  the  radicu- 
lar posterior  neurons 
can  enter  into  func- 
tional relationship 
with  each  other, 
either  directly  or  by 
the  intervention  of 
short  cells  of  associa- 
tion whose  ramifica- 
tions, both  those  of 
the  dendrites  and  of 
the  axis  cylinders, 
do  not  transgress  the 
boundaries  of  the 
ganglion.  These 
prolongations  of  the 
radicular  cells  would  further  provide  them  with  connexions  (still, 
however,  rather  ill  defined)  wdth  the  great  sympathetic. 

The  spinal  ganglia  thus  resemble  the  spinal  cord  in  structure,  and  they  are  in 
fact  a  portion  of  the  cord  embryologically  diverted,  and  therefore  possess  its 
functions  in  some  degree.     I  have  tried  exi^erimentally  to  ascertain  if  it  miglit 


C.  commis 


...  reflex 


Fig.  212. — Collaterals  of  the  posterior  roots. 

Diagram  of  groups  of  posterior  roots  giving  off  their  sliort, 
medium  and  long  collaterals  at  their  entrance  into  the  spinal  cord 
(Charpy). 


TACTILE    INNERVATION 


505 


still  be  possible  to  find  some  indication  of  the  obvious  transformatory  action 
possessed  by  the  spinal  cord  on  the  impulses  which  traverse  it  ;  and  with  this 
end  in  view  have  studied  the  characters  presented  by  the  reflex  responses  to 
stimuli  brought  to  bear  on  the  sensory  nerve  before  and  after  their  passage  through 
the  spinal  ganglion.  I  was  unable  to  discern  any  certain  modification  in  the 
most  prominent  features  of  the  reflex  movements  thus  obtained.  Either  the 
characters  under  observation  (latent  period,  fusion  of  impulses)  are  not  those 
which  depend  on  ganglionic  action,  or  else,  in  comparison  with  those  produced 
through  the  agency  of  the  spinal  cord,  these  modifications  are  too  feeble  to 
obviously    a  p  p  e  a  r    in    t  h  e 

tracings    of    muscular    move-  V.^i:_ -  Term,  arborizations 

ment  studied   in   this   double 
condition. 


2.  The  posterior  radicular 
fibres. — The  p  o  s  t  e  r  i  o  r 
radicular  fibres,  on  pene- 
trating the  spinal  cord, 
are  arranged  in  two 
groups,  of  which  the  one 
is  external  and  the  other 
internal,  these  groups 
differing  by  the  thickness 
of  their  fibres  and  the 
length  of  the  course  which 
they  run  in  the  spinal 
cord  before  going  to  rejoin 
the  various  areas  of  the 
grey  matter. 

The  type  of  their  con- 
nexions is  not  essentially 
different  in  the  short, 
medium,  or  long  fibres. 
These  last  form  the  group 
which  is  called  internal  or 
tnedian.  The  variations 
in  the  structural  type  must 
correspond  to  functional 
modalities,  of  the  nature 
of  which  we  are  ignorant. 


*  Long,  collal. 


Short  collat. 


Ascend,  br. 


Post.  root. 


-r-  VeKcenl.  br. 


Anterior  rod. 

Fig.  213. — Posterior  root  with  its  ascending  and 
descending  branches  and  their  collateral  and  ter- 
minal ramifications. 

extent  of  the 


Dispersion  of  the   impulse  over  a 
grey  axis. 


lar> 


\Yhen  studying  the  func- 
tion of  the  elements  of  the 
spinal  cord,  we  had  occasion 
to  speak  of  the  sensory  roots  and  their  principal  connexions. 

A  fact  which  we  owe  to  the  application  of  the  new  anatomical  methods,  and 
which  will  at  first  sight  cause  surprise,  is  the  extraordinarily  extended  develofment 


506  SPECIAL    INNERVATIONS 

of  tlie  polar  field  of  distribution  of  the  posterior  radicular  neurons  considered  in- 
dividually (principally  the  internal  gi'oup).  Some  of  these  extend  the  whole 
length  of  the  spinal  cord,  and  even  beyond,  in  order  to  reach  the  inferior  ntaclei 
of  the  medulla  oblongata,  or  perhaps  the  cerebelhun.  And  what  Avill  also  cause 
astonislunent  are  the  numher  and  varied  connexions  of  the  rccmifications  of  this 
field  of  distribution  with  the  grey  matter  of  the  spinal  cord,  so  that  the  principal 
regions  of  the  grey  matter  receive  the  expansions  of  the  same  polar  field. 

At  its  entrance  into  the  spinal  cord  the  posterior  radicular  fibre  is  divided  into 
two  branches,  one  descending,  shorter  (but  which,  nevertheless,  may  in  some 
cases  attain  more  than  5  to  7  centimetres)  ;  the  other  ascending,  whose  terminal 
extremity  attains  the  nuclei  of  Goll  and  of  Bm-dach  in  the  inferior  part  of  the 
medulla  oblongata.  These  branches  give  off  collaterals,  themselves  subdivisible 
into  short,  which  are  lost  in  the  posterior  horn  (substance  of  Rolando)  ;  medium, 
which  go  to  the  colvunn  of  Clarke  (a  small  mmiber  pass  through  the  posterior  grey 
commissure  and  form  a  commissural  tract)  ;  long,  which  run  to  the  anterior  horn 
of  the  same  side  (these  last  arise  near  the  bifiircation,  and  consequently  near  to 
the  root  which  has  produced  them,  and  hardly  leave  the  same  medullary  seg- 
ment). 

3.  Dispersion  of  the  stimulus. — The  nuclei  of  Goll  and  of  Burdach 
are  the  principal  origins  of  the  fillet  (ruban  de  Reil),  or  sensory  medullo- 
cortical  tract  ;  the  column  of  Clarke  is  that  of  the  direct  cerebellar 
tre.ct  ;  and  the  anterior  horns  of  the  spinal  cord  that  of  the  motor  roots. 
The  impulse  is  therefore  conveyed  to  tracts  which  disperse  it  in  three 
directions  as  divergent  and  remote  as  possible,  namely,  towards  the 
cerebral  cortex,  towards  the  cerebellum  and  towards  the  ynuscles,  these 
being  the  immediate  organs  of  movement.  Further,  this  same  grey 
matter  offers  it  the  dendrites  or  receptive  poles  of  numerous  neurons, 
whose  fibres  are  both  direct  and  crossed  ;  some  of  these,  long,  like 
those  of  the  tract  of  Gowers,  ascend  to  the  cortex  or  the  cerebellum  ; 
others,  medium,  unite  the  stages  of  the  spinal  cord  which  are  more  or 
less  distant  from  one  another  ;  and  still  others,  short,  associate  the 
elements  which  are  near  to  each  other  in  the  same  limited  area  of  the 
spinal  cord  for  the  discharge  of  extremely  varied  functions. 

The  dispersion  of  the  impulse  in  so  many  and  such  varied  directions, 
these  themselves  being  in  connexion  with  tracts  of  contrary  direction, 
which  concentrate  it  on  the  organs  executing  the  functions,  would 
engender  the  most  inextricable  disorder  in  these  functions,  were  not 
the  impulse  itself  governed  by  laws  whose  effect  we  can  observe,  but 
whose  principle  is  unknoA\Ti  to  us.  Sometimes  the  impulse  overflows 
to  the  brain,  and  seems  to  exhaust  itself  in  sensory  or  psychic  effects 
without  any  immediate  motor  results  ;  at  other  times  it  does  not  end 
in  the  consciousness,  but  without  delay  gives  rise  to  movement.  Be- 
tween these  two  extremes  there  is  room  for  the  most  varied  gradations 
and  combinations.  Anatomy  has  done  the  very  great  service  of  show- 
ing us  the  tracts  in  which  it  is  possible  for  the  impulse  to  become  in- 


TACTILE    INNERVATION 


507 


Collat.  commiss. 


volved,  in  order  that  it  may  realize  acts  as  diverse  and  as  contingent 
as  those  which  we  execute  both  internally  and  externally.  For  the 
verification  of  this  purely  static  state,  we  are  not  in  a  position  to  super- 
pose the  dynamic  conditions  answering  to  each  of  the  changes  of  which 
some  alone  are  visibly  and  externally  revealed  to  our  ej^es. 

Function  of  direction  or  of  shifting  of  the  points  [aiguillage). — The  obvious 
conception  of  these  changes  imphes,  as  regards  some  of  them,  the  existence  in 
the  nervous  system  of  a  function  of  direction  or  of  shifting  of  the  jDoints,  to 
employ  a  comparison  which  exactly  expresses,  but  in  metaphorical  terms,  the 
idea  required.  We  may  admit  this  in  jDrinciple  ;  only,  with  regard  to  the 
mechanism  of  this  function,  as  well  as  the  conditions  which  determine  its  execu- 
tion, positive  facts  are  at  present  altogether  lacking. 

The  determining  conditions  of  this  phenomenon  of  direction  are  not  all  in 
relation  to  the  actual  stimulus  (nature,  form,  intensity)  ;  some  of  them  are  in- 
ternal to  the  nervous  system  (at  the  moment  when  it  receives  the  stimulus)  ;  and 
thsse  conditions  seem  to  be  of  the  same  nature  as  those  which  take  part  in  the 
phenomenon  of  attention. 

4.  Short  circuit  ;  reflex  action. — When  the  impulse  brought  by  the 
long  collaterals  to  the  motor  nuclei  of  the  anterior  horn  finds  a  road 
for  going  to  the  muscles,  it  accomplishes  one  of  the  shortest  and  most 
simple  j  o  u  r  - 
neys  that  it 
can  perform  in 
the  nervous 
system.  The 
name  of  reflex 
collaterals  has 
been  given  to 
those  termina- 
tions of  the 
posterior  radi- 
cular neurons,  \  Motor  ce:t. 
which,  speak- 
ing generally, 
associate  the 
two  corre- 
sponding roots 
of  a  nerve  pair 
for  the  p  e  r- 
formance  of  a 

sensori-motor  act  of  the  most  simple  form.  That  the  impulse  really 
follows  this  route  maybe  demonstrated  by  isolating  the  metameric  seg- 
ment corresponding  to  the  nerve  pair  from  the  rest  of  the  spinal  cord  by 


Roland,  collat. 
Plexus  of  the  nucleus 

CoHa  .  of  Clarke 


Collat.  reflexes 


Fig.   "214. — Collateral  fibres  of  the  spinal  cord  (after  Cajal). 

Collaterals  of  the  columns  and  of  the  roots  seen  in  a  transverse  section 
of  the  thoracic  spinal  cord.     New-born  dog  (method  of  Golgi). 


508  SPECIAL    INNERVATIONS 

means  of  a  double  section  made  above  and  below  it.  But  it  must  not 
be  imagined  that  these  collaterals  are  the  only  reflex  paths  ;  all  the 
other  ramifications,  both  collateral  and  terminal,  of  the  posterior 
radicular  neuron  may  involve  the  impulse  in  circuits  which,  though 
more  unequal,  are  none  the  less  reflex  circuits. 

The  expression  "  reflex  act  "  is  generally  synonymous  with  an  un- 
conscious-voluntary act.  With  regard  to  this,  it  must  not  be  forgotten 
that  the  participation  of  the  brain  and  of  the  cortex  by  no  means 
necessarily  implies  a  conscious  element  in  the  sensory  and  voluntary 
manifestation  of  the  motor  phenomenon.  There  are  reflex  actions 
which  have  their  seat  in  the  cortex.  The  depth  of  its  penetration  is 
not  the  only,  or  the  determining,  condition  for  the  appearance  of 
consciousness  :  the  association  of  different  cortical  areas,  on  the 
contrary,  plays  here  a  part  of  the  first  importance. 

From  the  rudimentary  sensori-motor  phenomenon  which  operates 
in  the  isolated  medullary  segment,  up  to  the  phenomenon  of  ideation 
which  correlates  the  different  sensorial  systems  with  their  motor 
dependencies,  the  gradation  is  progressive  and  uninterrupted. 

5.  Long  circuit  ;  conscious  action. — When  stimulation  terminates 
in  a  conscious  phenomenon,  in  sensation,  the  latter,  as  already  men- 
tioned, may  present  three  modalities.  It  may  be  a  sensation  of  contact 
(cesthesia),  a  sensation  of  temperature  {thermo-oesthesia),  or  a  sensation 
of  pain  {algesia).  So  far  as  concerns  the  primary  paths  of  the  system 
(radicular  elements),  the  localization  of  the  stimuH  giving  rise  to  these 
three  sensations  into  three  orders  of  conductors  distinct  the  one  from 
the  other  has  been  given  up.  But,  starting  from  the  grey  medullary 
matter,  and  considering  the  somewhat  decided  morphological  differ- 
ences of  the  fasciculations  which  prolong  the  system  towards  the  en- 
cephalon,  it  has  often  been  hoped  that  a  distinct  functional  action  for 
each  of  these  might  be  found,  by  appropriating  it  to  the  isolated  trans- 
mission of  one  or  the  other  of  these  sensory  modalities.  And  not  only 
the  tracts,  but  also  the  grey  matter  has  been  compared  to  a  conductor, 
and  the  question  has  been  mooted  as  to  the  conducting  attributes  of 
the  grey  matter,  compared  with  those  of  the  tracts. 

Syringomyelic  dissociation  of  the  different  sensations. — The  most 
cogent  argument  that  can  be  brought  forward  in  favour  of  the  specific 
conduction  of  each  of  the  sensations  arising  in  the  skin  is  the  dissocia- 
tion which  they  undergo  from  the  presence  of  certain  changes  affecting 
the  spinal  cord  in  syri7igo7nyelia. 

This  is  a  disease  of  the  spinal  cord  in  which  disappearance  of  sensi- 
bility to  pain  and  temperature  rnay  be  observed,  tactile  sensibility  being 
retained.     The  lesion  which   causes   the  dissociation  is  a  gliomatous 


TACTILE    INNERVATION  509 

degeneration  which,  invading  the  grey  matter,  destroys  it  for  a  certain 
length,  replacing  it  by  cavities,  but  which  does  not  interfere  with  the 
white  matter. 

6.  Localizing  hypothesis.— This  is  the  reproduction  in  human  beings 
of  an  experiment  of  Schiff,  which  consists  in  cutting  away  (as  far  as 
possible)  the  grey  matter,  while  respecting  the  continuity  of  the  pos- 
terior columns.  The  result  would  be  the  same  in  both  cases  :  abolition 
of  certain  kinds  of  sensation  and  retention  of  others.  In  the  dog  thus 
operated  on,  tactile  sensibiHty  persists,  while  that  to  pain  is  lost. 
Hence  it  has  been  concluded  that  the  posterior  columns  are  those 
which  convey  tactile  impulses  (Schiff),  while  the  grey  matter  would 
be  the  path  for  impressions  of  sensibility  to  pain  (Brown-Sequard). 


Criticism. — This  view  was  for  some  time  very  favourably  regarded.  Clinicians 
found  in  the  experiment  of  Schiff  a  solid  basis  for  the  interpretation  of  the 
symptoms  of  syringomyelic  dissociation,  and  physiologists,  for  their  part,  found 
in  the  clinical  facts  and  those  of  pathological  anatomy,  a  support  for  conclusions 
which  were  not  in  themselves  obvious.  Unfortunately,  a  somewhat  rigorous 
criticism  of  these  facts  allows  hardly  anything  to  remain  of  the  fiindamental 
hypothesis.  Clinical  observations  indisputably  confirm  the  fact  of  the  dissocia- 
tion of  sensibility  to  pain,  to  temperature,  to  contact,  one  may  indeed  add,  to 
pressure,  to  heat,  to  cold  ;  in  a  M^ord,  to  all  the  known  varieties  of  sensation. 
The  sej^aration,  it  is  true,  is  not  always  complete  ;  but  in  most  cases  it  is  ex- 
tremelj'  distinct.  Only,  the  order  according  to  which  these  various  modalities  of 
feeling  group  themselves  or  disappear  is  not  always  the  same  ;  it  is  sometimes 
the  reverse  of  what  we  have  above  said  ;  in  that  case  it  would  be  tactile  sensi- 
bility which  would  be  involved,  without  any  change  in  the  sensibility  to  pain  or 
to  pressure.  Fvirther,  the  sensibility  to  cold  may  be  preserved,  and  that  to 
heat  destroyed. 

Discordance  between  symptoms  and  lesions. — If  to  each  varietj-  of  dissociation 
a  particular  form  of  lesion  of  the  sjiinal  cord  should  correspond,  nothing  would 
be  more  valuable  tlian  the  information  thus  furnished  by  pathologj*.  Unfortun- 
ately, if  the  varieties  of  gliomatous  degeneration  differ  amongst  themselves,  up 
to  the  present  time  no  certain  agreement  between  their  variations  and  those  of 
the  clinical  symptomatology  has  been  observed.  The  law  connecting  the  one 
with  the  other  has  not^been  determined  ;  this  law  is  therefore  not  that  which 
would  localize  the  different  orders  of  sensibility  in  dissociated  conductors,  and 
to  effect  this  would  liken  the  grey  matter  to  a  conductor.^ 

The  results  obtained  by  Schiff  in  the  experiment  in  question  are  not  such  as 
can  be  admitted  without  discussion.  Philippeaux  and  Vuljoian  declare  that 
they  have  seen  nothing  of  the  kind.  Xot  that  the  jiossibilitj-  of  these  results 
can  be  denied.     They  may  be  produced  by  experiments  on  animals,  in  the  same 


1  SjTingomvelia  (spinal  cord  assuming  the  form  of  a  pipe)  is  due  to  a  de\-elopment 
of  the  cells  or  neuroglia  of  the  grey  matter,  which  atrophies  and  disappears,  leaving 
cavities,  or  even  a  single  cavity  extending  the  whole  length  of  the  spinal  cord.  Some- 
times the  lesion  respects  a  portion  of  the  grey  matter,  sometimes  it  also  invades  the 
white  matter.  In  both  cases  it  more  or  less  compresses  the  latter.  It  is  maintained, 
but  without  very  clear  proof,  that  the  posterior  columns  suffer  less  than  the  others 
from  this  compression. 


510  SPECIAL    INNERVATIONS 

way  as  disease  produces  them  in  man  ;  but  the  conditions  ensuring  their  con- 
stancy are  not  exactly  determined  in  either  case. 

Equivocal  formula. — If  it  be  conceded  that  the  conditions  are  those  indicated 
above,  the  formula  indicating  them  is  badly  expressed.  It  places  in  opposition 
to  each  other  the  grey  matter  and  the  white  matter  of  the  spinal  cord,  as  if  tactile 
impressions  had  only  to  do  with  the  first  and  painful  impressions  with  the  second. 
In  reality  both  of  these  penetrate  into  the  spinal  cord  by  posterior  radicular 
elements,  which  form  part  of  its  wliite  matter,  and  by  these  are  necessarily  trans- 
mitted to  its  grey  matter. 

But  this  transmission  is  effected,  as  we  have  seen,  in  very  different  localities 
from  this  last-named  ;  certain  collaterals  reach  the  grey  axis  even  in  the  pro- 
longation of  the  roots,  while  others  reach  it  higher  up,  and  finally  the  terminal 
branches  only  at  the  level  of  the  bulb. 

The  localizing  theory  of  Schiff  and  Brown-Sequard  presupposes  that  impres- 
sions of  pain  find  in  the  grey  matter,  with  regard  to  the  roots  which  convey  the 
impulse,  or  in  their  more  or  less  immediate  neighbourhood,  a  path  of  transmission 
to  the  brain,  and  that  the  tactile  impressions  do  not  follow  this  route  ;  conversely, 
it  assumes  that  tactile  impressions  find  their  path  of  transmission  in  the  bulbar 
nuclei  or  in  their  neighboui'hood,  and  that  impressions  of  pain  do  not.  The  in- 
terruption of  the  grey  matter  between  the  level  of  the  root  under  consideration 
and  the  bulbar  region  will  therefore  suppress  the  conduction  of  painful  impressions 
after  their  penetration  into  the  grey  axis,  but  will  permit  of  the  penetration  of 
tactile  impressions.  Section  of  the  posterior  columns  at  the  same  level  will  sup- 
press the  conduction  of  tactile  impressions  before  their  penetration  into  the  grey 
axis,  but  will  leave  the  field  open  to  imjoressions  of  pain  ;  all  this  being  based  on 
the  hypothesis  of  their  localization  in  distinct  conductors  from  the  spinal  cord 
up  to  the  brain,  a  hypothesis  which  we  reject. 

7.  Bulbar  reflexes. — On  account  of  the  prodigious  extension  of  the 
polar  fields  of  the  posterior  roots,  the  impulse  conveyed  by  the  latter 
undergoes  a  first  dispersion  ;  the  grey  medullary  matter,  by  means 
of  the  fibres,  both  of  projection  and  of  association  arising  from  it  and 
which  follow  such  very  different  directions,  causes  it  to  undergo  a 
second  dispersion.  We  have  seen  that  a  choice  is  offered  it  by  the 
grey  matter  between  the  motor  nerves  which  pass  it  on  directly  to  the 
muscles,  or  the  encephalon  which  exerts  upon  it  a  power  of  conserva- 
tion, and  we  know  that  between  these  opposite  limits  it  has  other 
localities  for  transformation  and  for  reflexion  open  to  it.  The  medulla 
oblongata  is  one  of  the  most  important  of  these.  Rosenthal  describes 
it  as  taking  part  in  a  great  number  of  reflex  actions  which  it  has  been 
the  custom  to  regard  as  being  purely  medullary.  This  intervention 
is  particularly  observable  in  the  reflex  acts  which  react  on  the  great 
sympathetic  (vaso-motor,  secretory,  vaso-dilator  actions,  etc.). 

Experiment. — If  a  sensory  nerve  like  the  sciatic  or  any  other  nerve 
trunk  of  the  same  function  is  stimulated,  this  stimulation,  in  addition 
to  the  internal  or  purely  psychic  phenomenon  of  pain,  gives  rise  to  a 
large  number  of  reflex  manifestations,  both  as  regards  the  muscles  of 
the  skeleton,  including  those  of  respiration,  and  the  organs  discharging 


TACTILE    INNERVATION  511 

nutritive  functions.  In  order  to  appreciate  them  better  it  is  necessary 
to  dissociate  them.  The  most  prominent  of  these  manifestations  are 
suppressed  by  placing  the  animal  under  the  influence  of  curare,  which 
paralyses  the  voluntary  nerves  and  those  of  respiration.  Should 
then  a  phenomenon  of  painful  sensibility  be  provoked,  it  is  noticed 
that  the  heart's  action  is  slackened  (sometimes  it  may  even  be  stopped)  ; 
in  a  large  number  of  organs,  but  especially  in  the  viscera,  the  arterial 
capillaries  contract  and  cause  the  general  arterial  pressure  to  rise  ;  at 
the  same  time  the  cutaneous  capillaries  are  dilated,  and  congest  the 
circulation  in  the  superficial  regions  ;  the  pupil  is  dilated  ;  the  cutane- 
ous glands  secrete,  etc.  If  the  bulb  is  separated  from  the  spinal  cord 
by  section,  the  stimulation  no  longer  has  the  same  effect.  If,  after  a 
certain  interval,  the  experiment  is  recommenced,  it  will  be  seen  that 
the  effects  reappear,  but  are  less  marked.  This  is  a  proof  that,  as 
concerns  all  these  actions  of  organic  life,  the  medulla  oblongata  is  an 
important  centre  of  reflexion,  but  that  it  is  nevertheless,  not  the  only 
one,  although  its  action  in  this  respect  predominates  greatly  over  that 
of  the  spinal  cord. 


B.     TATICLE    CORTICAL    AREA 

The  impulses  received  from  the  surface  of  the  skin  do  not  all  reach 
the  cerebral  cortex  ;  a  large  number  of  them  are  dispersed  or  reflected 
at  variable  altitudes,  from  the  spinal  cord  in  passing  through  the 
cerebellum  and  the  cerebral  ganglia.  Those  which,  after  numerous 
transformations  in  the  subjacent  layers  of  the  grey  matter,  reach  the 
cortex,  there  give  rise  to  the  phenomenon  of  tactile  sensation  called 
general  sensibility,  in  opposition  to  the  other  sensations  which  arise 
from  impressions  of  a  different  nature,  collected  on  more  limited 
surfaces  (special  sensations) . 

1.  Cortical  localization  of  sensation. — It  is  maintained  that  tactile 
sensation  is  developed  in  a  limited  and  determinate  area  of  the  cerebral 
cortex  ;  which  is  as  much  as  to  say  that,  after  the  destruction  of  this 
cortical  area,  the  clear,  distinctly  conscious  sensation  of  touch  will  no 
longer  be  present.  If  the  injury  should  affect  one  of  the  two  hemi- 
spheres, there  will  be  ansesthesia  of  one  of  the  two  sides  of  the  body  ; 
should  both  the  hemispheres  be  injured,  the  ancesthesia  will  be  general- 
ized. 


Tlie  delimitation  of  the  tactile  cortical  area  (tactile  sphere  of  Munck,  centre 
of  tactile  sensation  of  many  authoi's)  has  given  rise  to  much  discussion.  For 
reasons  somewliat  theoretical,  it  was  at  first  located  in  the  i^osterior  part  of  the 


512 


SPECIAL    INNERVATIONS 


brain  behind  the  excitable  motor  area  (doubtless  by  analogy  with  what  is 
observed  in  the  spinal  cord).  Facts,  both  clinical  and  experimental,  compelled 
the  abandonment  of  this  theory,  and  the  area  of  tactile  sensation  is  now  known 
to  be  confounded  with  the  motor  area  itself  ;  or,  to  put  it  otherwise,  is  located 
in  the  central  convolutions  situated  in  the  immediate  neiglibovirhood  of  the 
fissure  of  Rolando. 

Sensori-motor  area. — The  clinical  facts  on  which  this  localization 
has  been  founded  are  due  more  especially  to  the  researches  of  R.  Tripier 
(1880).  From  the  first,  and  in  spite  of  the  predominance  of  a  contrary 
view,  this  observer  has  held  that  motor  paralyses  (hemiplegias),  caused 
by  a  destruction  of  the  Rolandic  area,  are  constantly  accompanied 
with  a  diminution    of    sensation  :    this  hyposesthesia  being,  not  the 


Fig.  215. — Sensori-motoi-  and  sensorial  areas  of  the  external  siu'face  of  the  heniisjihere. 

Sensori-motor  tactile  area  subdivided  into  three  regions. 

MI,  area  for  the  inferior  limb  ;    MS,  area  for  the  superior  limb  ;    F,  area  for  the  face  ;    AC, 
sensorial  area  of  audition  (after  Dejerine). 


exception,  but  the  rule.  The  7notor  area  is  in  reality  a  sensori-motor 
area.  Physiological  facts,  after  the  most  careful  examination,  point, 
as  Luciani  and  Munck  have  found,  in  the  same  direction.  The  destruc- 
tion of  the  motor  area  is  followed  by  effects  recognizable,  not  only  in 
the  domain  of  motricity,  but  also  in  that  of  sensibility  ;  it  must,  how- 
ever, be  borne  in  mind,  that  the  expressions  motricity  and  sensibility 
have  a  meaning  which  is  sometimes  extended  to  every  production  of 
movement  and  to  every  phenomenon  of  reaction  against  external 
stimulation  ;  this  acceptation  may  sometimes,  on  the  contrary,  be 
limited  to  certain  modalities  of  movement  or  of  the  reaction  which 
reveals  sensibility  to  us. 


TACTILE    INNERVATION 


513 


The  destruction  of  the  motor  area  in  an  animal  allows  of  the  per- 
sistence of  a  large  number  of  movements  of  very  varied  functional 
modality  ;  some  of  these  movements  are  simple,  and  others  com- 
plicated ;  all,  however,  are  co-ordinated  and  adapted  to  a  given  end. 
Even  motor  spontaneity  does  not  seem  to  have  disappeared,  which 
fact  proves  that  the  sources  of  stimulation  have  remained  numerous 
and  of  varied  character  ;  but  certain  modalities  of  movement  (especi- 
ally that  executed  by  the  limbs)  have  disappeared  for  ever,  and  the 


Fig.   21G. — Sensori-niotor  and  sensorial  areas  of  the  mesial  sixrface  of  the  hemisphere. 

MI,  paracentral  lobule  forming  part  of  the  sensori-niotor  tactile  area. 
V,  visual  area  ;    O,  olfactory  area  (after  Dejerine). 

corresponding  motor  paralysis  will  only  appear  after  search  for  these 
movements  amongst  others  more  or  less  resembling  them. 

The  destruction  of  the  so-called  motor  area,  which  we  describe  with 
Tripier  as  sensori-motor,  also  allows  of  the  continuance  of  a  certain 
number  of  defensive' or  responsive  movements  on  the  part  of  the 
animal,  these  being  often  considered  as  evidence  of  sensibility  ;  but, 
as  the  author  just  mentioned  has  observed,  it  will  suppress  a  certain 
number  which  will  never  reappear,  both  in  the  dog  and  in  man.  It 
is  for  these  that  search  should  be  made  if  it  be  desired  to  recognize  and 
define  the  sensory  paralysis  following  the  cortical  lesion  thus  produced. 


Progressive  differentiation  in  the  series. — Tlie  sensori-motor  phenomena 
depending  on  the  sensorial  areas  in  general,  and  on  the  tactile  area  in  particular, 
have  an  importance,  and  a  distinct  physiognomy  all  the  greater  in  proportion 
as  to  whether,  in  any  given  individual,  they  correspond  to  a  more  differentiated 
and  more  frequently  exercised  function.     It  is  only  under  these  conditions  that 

P.  •  L  L 


514  SPECIAL    INNERVATIONS 

the  deficiency  will  appear  pennanently,  in  the  domain  both  of  niotricit y  and  of 
sensibility.  It  will  be  much  more  apparent  in  man  than  in  the  monkey,  and  in 
the  monkey  than  in  the  dog  ;  below  the  latter,  it  is  hardly  worth  while  seeking 
it  in  the  case  of  lesions  limited  to  a  circmnscribed  area  of  the  cortex.  It  will 
appear  in  man  much  more  obviously  in  the  arm  than  in  the  leg,  and  in  the  hand 
and  the  fingers  much  more  than  in  the  other  segments.  In  animals,  also,  it  must 
be  sought  in  the  extremities  (Mott). 

Functional  balance. — This  is  one  of  the  exami:)les  of  the  law  to  which  we  have 
already  had  occasion  to  allude.  The  cerebral  functions,  those  which  create 
animality,  and  above  that  again,  humanity,  are  nothing  but  the  primordial 
fmictions  of  the  nervous  system,  slowly,  but  progressively  and  deeply,  differen- 
tiated ;  in  the  same  way  that  the  brain,  which,  to  begin  with,  was  onl\-  some 
sort  of  a  segment  of  the  nervous  axis,  has  assumed  an  adaptation,  a  development 
and  special  connexions,  to  prepare  it  for  the  directive  role  which  it  should  assume 
in  the  superior  species. 

The  ganglia  of  the  great  sympathetic,  the  segments  of  the  spinal  cord,  have 
remained  as  evidence  of  the  jorimitive  organization.  In  spite  of  being  penetrated 
and  invaeled  in  every  layer  by  bundles  of  projection  which  bring  them  into  in- 
dividual subjection  to  the  superior  segment,  now  become  the  brain,  these  organs 
still  preserve  traces  of  their  independence  and  also  of  their  federation.  But 
their  autonomy  (both  individual  and  collective)  has  been  much  diminished  even 
here,  and  has  given  way  to  a  more  pronounced  centralization.  This  is  why  the 
functional  deficiency  following  the  destruction  of  the  cerebral  cortex  in  the 
superior  species,  and  especially  in  man,  is  so  pronounced. 

The  functional  substitutions,  which  are  easily  effected  between  similar  organs, 
or  those  only  slightly  different,  become  impossible  between  organs  which  have 
vmclergone  a  double  inverse  evolution  (retrogressive  for  some,  progressi\-e  for 
others)  which  has  thus  prof  ovindly  differentiated  them.  It  maybe  added  that 
this  differentiation  is  of  unequal  value  for  the  various  cortical  functions,  and 
therefore  for  the  diverse  systems,  areas  and  organs  by  which  these  functions 
are  execiited  ;  this  is  what  causes  the  unequal  disturbances  following  lesions 
which  seem  ecjual  or  equivalent. 

2.  Imperfect  superposition  of  sensory  and  motor  areas. — If  the 
cortical  area  of  tactile  sensibility  is  superposed  to  that  of  the  so-called 
motor  area  of  the  brain,  it  is  well  to  add  that  it  is  not  superposed  to  it 
in  an  exact  manner  ;  or,  to  put  it  better,  we  have  no  absolutely  certain 
criterion  for  tracing  distinct  limits  around  either  one  or  the  other  of 
these  territories.  Further,  we  know  that  these  limits  do  not  exist  in 
a  sharply  defined  condition,  but  that  they  are  formed  by  a  continuous 
degradation.  Apparently  the  sensory  area  extends  far  beyond  the 
motor  area.  This  seems,  at  all  events,  the  conclusion  which  is  deducible 
from  the  following  observations  :  for  equal  lesions  the  sensory  paralysis 
is  less  evident  and  of  less  extent  than  is  the  corresponding  motor  paralysis  ; 
it  is  also  more  transitory  ;  and,  after  having  been  very  distinct,  it 
may  to  a  large  extent  disappear. 

Difficulties  of  comparison. — It  must  also  be  recognized  that  means 
of  comparison  are  too  often  wanting.  Like  sensibility,  motricity  is 
of  various    kinds  :     according  to  the  modality  assumed,    the  motor 


TACTILE    INNERVx\TION 


515 


or  sensory  phenomena  may  be  affected  more  or  less  gravely  by  the 
cerebral  lesion,  or  be  to  a  great  extent  respected  by  it.  Speaking  of 
sensibility  alone,  a  difference  must  be  drawn  between  algesia  and 
thermo-cBsthesia,  which  generally  resist  even  extended  lesions,  and 
touch  properly  so  called,  which,  other  things  being  equal,  is  more  com- 
promised. Again,  we  must  distinguish  between  the  sensation  of  con- 
tact and  that  of  active  touch,  or  the  faculty  we  possess  of  localizing 
objects,  and  of  associating  in  the  same  representation  muscular  and 
tactile  sensations.  This  last  modaHty  is  the  one  which  disappears 
most  readily,  and  in  the  most  persistent  manner. 


F2 


Fl 


Line  corresponds  to 
.  iissure  of  Roland. 


Fig.  217. — Cranio-cerebral  topography. 
Rolandic  line  and  Sylvian  line  (after  Poirier). 


Data  furnished  by  anatomy. — Again,  the  sensori-motor  natiu-e  of  the  Ro'andic 
area  is  demonstrated  by  anatomical  data.  The  fillet  (ruban  de  Reil),  the  pro- 
longation in  the  brain  of  the  sensory  tracts  of  the  spinal  cord,  spreads  itself  out 
in  the  central  convolutions  ;  this  is  demonstrated  by  the  facts  of  embryology 
and  the  study  of  degenerations  made  both  in  man  and  in  animals. 

In  reality  the  fillet  is  composed  of  two  bvmdles  arising,  one  in  the  grey  matter 
of  the  spinal  cord  (lateral  fillet),  the  other  in  the  lower  portion  of  the  bulb  in  the 
nuclei  of  Goll  and  of  Burdach  (mesial  fillet),  which,  on  leaving  this,  are  united 
together  and  then,  following  the  crm'a  cerebri  and  the  internal  capsule,  proceed 
to  the  cortex.     Flechsig  has  followed  the  former  (lateral  fillet)  as  far  as  the  ascend- 

LL* 


516  SPECIAL    INNERVATIONS 

ing  parietal  convolution  and  to  some  neighbom'ing  areas.  The  second  (mesial 
fillet)  also  joins  the  cortex  in  tlie  central  convolutions,  but  the  larger  part  of  its 
fibres  are  interrupted  in  the  optic  thalamus.  From  the  bulb  to  the  optic  thala- 
mus a  hulho-thalamic  neuron  extends,  and  from  the  optic  thalamus  to  the  cortex 
a  thalanio-cortical  neuron.  Destruction  of  the  central  convolutions  involves  a 
retrograde  degeneration  of  this  second  neuron,  and  an  atrophy  of  the  first  with- 
out degeneration  properly  so  called.  However  this  may  be,  the  tactile  area  is 
represented  by  a  territory  of  the  cortex  which  receives  the  terminations  of  the 
sensory  paths  (fillet,  rviban  de  Reil)  and  the  origins  of  the  motor  paths  (pj'ra- 
midal  tract). 

3.  Another  localizing  formula. — When,  according  to  facts  furnished 
chnically  and  experimentally,  the  motor  and  the  sensory  areas  were 
confounded  in  one  single  sensori-motor  area,  the  hope  was  not  on  that 
account  renounced  of  formulating  a  new  theory  which  would  reconcile 
with  these  facts  the  conception  of  a  separate  localization  of  sensibility 
and  motricity.  At  one  time  it  was  thought  to  have  been  found  in  a 
division  in  depth  of  the  so-called  centres  fulfilling  one  or  the  other 
function,  the  most  superficial  lesions  of  the  cortex  being  those  which 
are  often  accompanied  with  insensibility  (Brissaud).  Whether,  with 
Golgi  and  Tamburini,  motricity  and  sensibility  be  represented  as 
cellular  functions,  or  whether,  with  Flechsig,  they  be  considered  as 
functions  of  association,  the  conception  which  still  predominates  in 
many  minds  is  that  of  a  separate  and,  in  some  sort,  absolute  localiza- 
tion, and  of  a  dissociation  of  the  areas  or  fields  of  the  two  functions,  one 
of  these  fields  terminating  at  the  precise  limit  where  the  other  begins. 

Critical  examination. — I  have  already  shown  that  this  conception, 
which  aims  at  the  extension  to  the  deep  masses  and  to  the  cortex  of 
the  brain  of  the  results  of  experiments  made  on  nerve  roots,  is  un- 
tenable. The  radical  distinction  which,  at  the  first  glance,  is  seen  to 
exist  between  movement  and  sensibility,  should  not  lead  us  to  ignore 
the  necessary  link  which  unites  them.  To  less  superficial  examination 
this  link  declares  itself  under  numerous  aspects  ;  it  exists  both  in  the 
partial  or  general  elements  and  systems  as  well  as  in  the  nervous  system 
taken  as  a  whole.  In  the  cell,  whether  considered  in  an  isolated 
manner  or  experimentally  separated,  this  link  is  the  basis  of  what  we 
call  its  irritability.  The  cell  responds  by  a  movement  to  the  stimulus 
coming  from  without,  and  thus  reveals  its  state  of  irritation.  In  the 
nervous  system  and  the  large  component  systems  resembling  it  this 
link  is  quite  as  important ;  but,  on  account  of  the  complexity  of  the 
systems  involved,  it  allows  of  its  principal  methods  of  articulation 
being  better  seen.  To  my  mind  the  error  lies  in  considering  this  arti- 
culation as  single  and  in  locating  it  according  to  a  plane  of  division 
(marked  out  in  the  cerebral  cortex)  which  displaces  the  two  phenomena, 


TACTILE    INNERVATION  517 

the  one  in  front,  and  the  other  behind  it.  The  reciprocal  penetration 
of  the  two  phenomena  is  effected  by  roots  which  are  prolonged  in  the 
two  directions  up  to  the  confines  of  the  nervous  system.  The  cerebral 
cortex  nevertheless  remains  the  most  remarkable  locality  of  this 
system,  but  for  reasons  rather  different  to  those  which  have  been 
assigned.  It  does  not  contain  in  itself  the  boundary  or  surface  of 
demarcation  of  sensory  phenomena,  but  ought  to  be  considered  as  the 
keystone  of  the  systems  giving  to  sensation  its  highest  expression, 
which  preserve  it  under  the  form  of  images,  and  finally  attach  it  in 
time  to  the  movements  by  which  it  always  has  to  manifest  itself. 

If  we  imagine  a  section  made  with  a  sharp  instrument  following  the  ideal 
sxirface  supposed  to  exist  in  the  cortex  between  the  sensory  and  motor  field,  we 
then,  according  to  current  ideas,  should  bring  about  in  an  effective  and  per- 
manent manner  this  dissociation  of  sensibility  and  movement  as  it  is  visually 
conceived  and  as  it  is  considered  to  exist  at  certain  moments  in  the  nervous 
.system. '^  But  such  an  operation  (it  is  vxnnecessary  to  observe  that  it  is  wholly 
unrealizable)  would  not  allow  of  the  subsistence  either  of  sensibility  under  the 
highly  differentiated  forms  which  are  presided  over  by  the  cerebral  cortex,  or  of 
movement  under  the  equally  superior  form  known  as  voluntary.  In  affirming 
this  I  use  as  a  basis  the  conception  which  ought  to  be  held  of  the  partial  systems 
composing  the  nervous  system,  inasmuch  as  these  systems  are  self-sufficing  and 
capable  of  an  independent  function. 

Functional  systems,  their  characteristic. — The  assemblage  of  sensory  roots  is 
a  systematization  bringing  near  together  elements  of  a  definite  type  ;  the  as- 
semblage of  the  motor  roots  is  the  same.  Tlie  first,  surmounted  by  paths  which 
prolong  it  up  to  the  brain,  or  the  second,  surmounted  by  descending  paths  which 
proceed  from  the  cortex,  are  mqre  complicated  systematizations  than  the  pre- 
ceding ones  (they  form  what  in  other  words  is  called  the  sensory  and  the  motor 
field)  ;  but  they  are  not  yet  systems  in  the  proper  sense  of  the  word.  On  the 
other  hand,  a  sensory  root  associated  with  a  motor  root  in  the  execution  of  an 
elementary  reflex  action,  represents  a  fu.nctionally  definite  system.  That,  then, 
which  characterizes  a  system  in  the  physiological  sense  of  the  word,  is,  on  the 
one  hand,  the  association  of  sensibility  with  movement,  and,  on  the  other,  the  cyclic 
form,  which  jilaces  the  two  phenomena  in  mutual  dej^endence  by  causing  them 
to  succeed  and  engender  each  other  reciprocally. 

Typical  form. — The  reflex  cycle  is  thus  the  prototype  of  the  nervous  organiza- 
tion and  it  is  found  from  top  to  bottom  of  this  organization.  Functionally  dis- 
sociated, the  nervous  system  furnishes  cycles  of  this  kind  both  in  its  superior 
and  in  its  inferior  portions  :  some  are  simple  and  rudimentary  ;  others  are  com- 
plex and  formed  by  the  association  of  the  first  ;  neither  of  them,  however,  is 
capable  of  isolated  independent  function,  excepting  in  so  far  as  it  retains  the 
cyclic  form  and  organization,  at  least  in  a  certain  degree. 

1  It  may,  on  the  other  hand,  be  observed  that  such  a  surface  is  not  traceable  in  any 
manner,  not  even  ideally,  if  it  is  intended  to  follow  the  articulations  of  *he  neurons 
(sensory  on  one  hand,  motor  on  the  other)  and  at  the  same  time  to  respect  the  con- 
tinuity of  the  cerebral  elements.  It  must,  indeed,  be  remembered  that  the  terminal 
poles  of  the  one  (axons  of  the  fillet),  and  initial  poles  of  the  others  (dendrites  of  the 
pyramidal  tract),  in  addition  to  the  contacts  which  enable  them  to  transmit  the  impulse 
in  a  direct  manner,  are  further  attached  in  a  secondary  fashion  by  elements  of  associa- 
tion of  all  shapes  and  dimensions,  which  we  cannot  place  exclusively  either  in  the  sensory 
or  in  the  motor  field,  and  which  consequently  will  be  found  in  the  course  of  the  section. 

L  L** 


518  SPECIAL    INNERVATIONS 

4.  Apparent  dissociation  of  sensation  and  motion. — The  dissociation 
of  sensation  and  movement  is  effected  in  an  apparently  very  definite 
manner  in  the  two  following  circumstances  :  (1)  external  stimuli 
applied  to  our  sensory  nerves  provoke  in  us  conscious  sensations  which 
are  not  followed  by  movement,  by  muscular  effort  ;  (2)  movements 
are  produced  in  our  muscles  by  internal  voluntary  stimulation  of  the 
motor  system  apart  from  any  excitation  from  without  by  the  path 
of  the  senses. 

This  double  observation  which  every  one  can  make  on  his  own  person, 
seems  at  first  sight  to  correspond  as  exactly  as  possible  to  the  anatomical 
scheme  which  divides  the  nervous  system  into  two  sub-systems,  one 
devoted  to  the  exclusive  localization  of  sensation,  the  other  to  that 
not  less  exclusive  of  motion. 

But  this  exclusive  localizing  conception,  and  the  absolute  dissociation 
which  it  implies  between  sensibility  and  motricity,  is  in  reality  only 
based  on  outside  show  ;  it  does  not  survive  a  somewhat  searching 
analysis.  Indeed,  as  regards  sensibility,  it  is  easy  to  verify  the  fact 
that  all  sensation,  such  as  that  resulting  from  a  rather  lively  external 
impression,  is  followed  by  a  tendency  to  movement,  if  not  by  actual 
movement  itself.  This  is  a  proof  that  the  nervous  system  is  affected 
in  a  cyclic  manner  in  its  superior  portion  ;  the  impulse  overflows  the 
cortex,  and  becomes  partially  involved  in  the  motor  paths,  since  the 
muscles  themselves  reveal  a  trace  of  it. 

So  far  as  concerns  the  so-called  voluntary  stimulation  of  our  move- 
ments, we  have  also  no  reason  to  believe  that  this  excitation  has  its 
immediate  starting-point  in  the  motor  system,  to  the  exclusion  of  the 
so-called  sensory  elements  of  the  brain.  Will  imphes  memory,  that 
is  to  say,  the  awakening,  the  recalling  to  existence,  of  one  or  many 
anterior  sensations. 

Contrary  to  strong  sensation,  which  is  often  only  followed  by  a  sug- 
gestion of,  or  by  a  tendency  to  movement  without  any  muscular  effort 
properly  so  called,  it  is  a  weak  sensation  coming  on  without  external 
stimulation,  but  followed  by  effective  movements  more  or  less  energetic 
and  complicated.  It  thus  implies  a  cerebral  process  of  a  cyclic  form, 
although  in  certain  respects  differing  from  the  preceding  one. 

Inequality  of  the  cycles. — The  two  cycles,  in  the  examples  thus  arbitrarily 
chosen  for  the  requirements  of  analysis,  are  unusual  in  that  tliey  have,  in  the 
sensory  and  motor  field,  prolongations  which  are  not  equal,  but  inversely  un- 
equal. They  have  a  common  cerebral  sensori-motor  portion  ;  to  this  portion, 
which  is  of  a  strictly  cyclic  form,  we  see  added,  as  regards  the  first,  sensory 
peripheral  paths  from  their  origin,  and  as  concerns  the  second,  motor  paths  up 
to  their  termination  ;  the  motor  peripheral  paths  being,  as  it  were,  abstracted 
from  the  first,  and  the  peripheral  sensory  paths  from  the  second.     In  the  first 


TACTILE    INNERVATION  519 

an  actual  sensation  creates  a  potential  motricity  ;  in  the  second,  it  is  an  actual 
niotricity,  which  has  for  its  origin  potential  stimuli  deposited  in  the  brain  by 
anterior  sensations.  The  link,  in  time,  between  sensation  and  movement 
operates  precisely  through  the  permanent  cyclic  system  which  we  call  cerebral. 

Extension  in  surface  and  depth. — The  extension  in  sm*face  and  in  depth  of 
the  cerebral  cycles  is,  as  may  be  supposed,  infinitelj'  variable,  according  to  the 
nature,  the  importance,  and  the  complication  of  the  nervous  acts  considered  in 
an  isolated  manner.  Tliere  are  some  which  probably  do  not  pass  beyond  its 
thickness  and  remain  confined  in  restricted  areas.  There  are  others  wliich 
mutually  connect  its  different  convokitions,  whether  neighbouring  or  distant, 
at  the  same  time  that  they  connect  them  with  the  corpus  striatum,  the  optic 
thalamus,  the  cerebellum  and  the  spinal  cord  in  co-ordinated  actions. 

In  principle,  it  is  maintained  that  the  most  highly  differentiated  nervous 
functions  are  those  which  demand  the  most  extended  associations,  and  occupy 
the  largest  areas  in  the  brain.  For  all  concerning  the  surface  associations  this 
cannot  be  doubted,  and  the  constitution  of  the  area  for  language  will  furnish 
an  example  of  it  ;  but  for  the  deep  associations  it  is  better  to  speak  much  more 
reservedly  ;  one  thing,  however,  is  certain,  viz.  :  that  intelligence  is  compatible 
with  curtailments  or  extensive  injuries  of  the  spinal  cord,  the  cerebellum  and 
the  cerebral  ganglia. 

The  associations  which  are  affected  in  the  brain  and  its  cortex  arise,  some 
between  the  symmetrical  and  others  between  the  unsymmetrical  portions.  The 
first  duplicate  in  some  way  (and  in  a  symmetrical  manner)  the  execution  of 
the  functional  nervous  act  which  is  represented  in  these  parts  ;  at  the  same 
time  adding  nothing  to  its  complication  or  to  its  value.  It  is,  on  the  contrary, 
the  second  which  give  it  (as  may  be  gathered)  its  functional  differentiation. 
The  area  for  speech  is  also  a  proof  of  this.  The  differentiation  presented  by  it 
is  carried  to  such  a  degree,  that  this  centre  is  confined  to  one  of  the  two  hemi- 
spheres, to  the  exclusion  of  the  other  ;  this  latter,  therefore,  is  unable  to  par- 
ticipate in  the  execution  of  vocal  signs,  nor,  consequently,  can  it  supplv  the 
place  of  the  differentiated  centre,  .should  this  be  destroyed. 

5.  Multiple  connexions. — The  cortical  area,  corresponding  to  these 
limits,  is  then,  by  definition,  the  site  of  the  connexions  between  the 
ascending  and  the  descending  paths  of  the  tactile  system  ;  but  this 
association,  primitive  and  habitual  though  it  be,  is  not  the  only  one 
which  can  be  effected  here.  By  means  of  the  fibres  of  association 
which  connect  it,  through  the  brain,  with  the  other  sensorial  cortical 
areas,  it  can  effect  sensori-motor  combinations  other  than  that  which 
serves  as  a  basis  for  the  present  description.  It  has  the  power  of  plac- 
ing its  motor  paths  at  the  disposition  of  another  sense  (hke  sight  or 
hearing),  or  of  borrowing  those  proper  to  these  senses,  to  attach  them 
to  the  tactile  sensation  in  some  special  act.  For,  in  the  same  way  as 
there  are  on  the  surface  of  the  brain  a  certain  number  of  sensorial  areas 
(as  many  as  there  are  distinct  senses),  there  are  also  a  corresponding 
number  of  motor  areas,  or  zones,  each  of  these  areas  being  sensori- 
motor, just  as  the  tactile  area  is  sensitivo-motor. 

Only,  the  muscular  forces  at  the  direct  disposition  of  the  senses 
other  than  that  of  touch  being  of  such  small  account  (muscles  of  the 


520  SPECIAL    INNERVATIONS 

■ears  and  of  the  eyes)  in  comparison  with  the  number,  the  extent,  and 
the  power  of  the  muscles  attached  to  the  sense  of  touch,  the  name  of 
motor  centre  or  cortical  motor  area  is  in  some  degree  reserved  for 
that  part  of  the  cortex  which  controls  the  latter. 

Effects  of  destruction. — Whatever  may  be  the  realizable  connexions, 
the  destruction  of  the  central  convolutions  severs  at  their  origin  in 
the  cortex  the  cortico-bulbar  and  the  cortico-medullary  conducting 
paths  which  govern  the  voluntary  muscles  of  the  skeleton  ;  hence 
arises  the  special  kind  of  paralysis  by  which  they  are  attacked.  The 
same  lesion  severs  at  their  termination  the  bulbo-cortical  conductors, 
which  convey  the  impressions  received  in  the  skin  ;  hence  arises  the 
anesthesia  which  is  simultaneously  the  consequence  of  it. 

6.  Isolation. — The  sensitivo-motor  tactile  area  in  this  way  presents 
connexions  either  with  the  grey  axis  or  with  the  other  sensorial  areas  ; 
it  is  capable  of  exchanging  impulses  either  with  the  first  or  with  the 
second,  by  fibres  which  are  both  efferent  and  afferent.  Experiments 
have  been  performed  for  the  purpose  of  ascertaining  how  much  subsists 
and  what  disappears  of  its  activity  when  these  connexions  are  inter- 
rupted either  as  regards  depth  or  surface.  Fran9ois-Franck,  Pitres, 
Marique  and  others  have  cut  both  the  radiating  fibres  of  projection 
which  go  to  the  grey  axis  (by  a  deep  section  perpendicular  to  their 
direction)  and  the  tangential  fibres  of  association  (by  a  circular  incision 
effected  around  the  tactile  so-called  motor-area). 

There  is  one  point  on  which  these  authors  are  entirely  agreed  ;  that 
is  concerning  the  results  of  stimulation  of  the  tactile  area  effected  in 
both  cases  immediately  after  these  sections.  Section  of  the  tangential 
fibres  alone  does  not  prevent,  hut  that  of  radiating  fibres  causes  the  dis- 
appearance of  the  motor  effects  produced  by  the  stimulation  of  the  sensori- 
motor tactile  area.  This  is  a  proof  that  an  impulse  when  originating  in 
the  tactile  area  follows  the  course  of  the  radiating  fibres,  and  not  a 
round-about  route,  when  going  to  the  grey  axis  which  transmits  it  to 
the  muscles  by  its  motor  nerves  ;  in  other  words,  its  action  on  the 
grey  axis  is  a  direct  one,  and  this  result  is  in  entire  accord  with  the 
teachings  of  anatomy. 

There  is  less  unanimity  as  regards  the  functional  modifications  which 
ensue  consecutively  to  these  operations.  It  is  true  that  for  both, 
section  of  the  fibres  of  projection  paralyses  the  sensori-motor  area,  and 
that  of  the  fibres  of  association  allows  of  something  of  its  activity  being 
retained  ;  but  while  FranQois-Franck  and  Pitres  are  especially  im- 
pressed by  the  preservation  of  functions  in  the  isolated  area,  to  which, 
according  to  their  view,  a  certain  directive  action  over  movement  is 
still  attached,  Marique,  Exner  and  Paneth,  on  the  contrary,  insist  on 


TACTILE    INNERVATION  521 

the  deficiency  following  such  an  isolation,  which  deficiency  they  com- 
pare to  that  observed  after  the  ablation  of  the  sigmoid  gyrus,  though 
at  the  same  time  recognizing  that  it  is  less  marked. 

The  points  of  view  taken  by  these  authors  are  different,  but  the  results  are 
not  contradictory.  The  isolation  of  the  tactile  area  from  the  rest  of  the  cortex 
allows  the  persistence  of  a  system  (the  tactile  system  properly  so  called)  lohich 
may  still,  once  isolated,  act  in  an  autonomous  manner,  its  functions  being  neces- 
sarily imperfectly  performed. 

For,  as  Exner  has  remarked,  if  the  sources  of  motor  stimulation  are  situated 
partly  in  the  organs  of  touch,  they  exist  to  a  still  gi-eater  extent  in  the  other 
different  senses,  which  exercise  a  conscious  control  over  movements.  Once 
isolated  from  all  these  senses,  the  tactile  system,  reduced  to  its  own  resources, 
will  every  moment  reveal  its  inability  to  execute,  by  itself  alone,  the  functions 
which  were  previously  performed  in  concert  with  all  the  others.  It  performs 
its  functions,  but  in  an  imperfect  manner. 

Primary  and  secondary  sensations. — Sensibility  is  at  the  foundation  of  move- 
ment ;  but  movement,  in  its  turn,  reacts  on  the  nervous  system  under  the 
form  of  sensation.  There  are,  as  Bastian  remarks,  primary  sensations  which 
give  rise  to  movement,  and  secondary  sensations  which  are  caused  by  it,  and 
which,  lodged  in  the  nervous  system,  will  serve  as  gviides  for  a  fresh  perform- 
ance of  a  similar  movement.  The  first  can  only  arise  from  the  organs  by 
which  we  are  placed  in  relation  with  the  exterior,  that  is  to  say,  the  organs  of 
the  senses,  properly  so  called  ;  the  second  come  to  us  from  our  own  organs. 
In  fact,  not  only  the  skin,  but  also  the  muscles,  the  tendons,  the  ligaments,  and 
the  sm-faces  of  the  articulations  are  provided  with  sensory  nerves,  which  gather 
together  and  convey  towards  the  brain  the  internal  impulses  dvie  to  movement 
itself.  From  this  result  post-motor  sensations,  which  have  been  called  ccena^s- 
thetic.  Like  those  arising  from  all  the  other  senses,  these  impressions  are  stored 
v^p  in  the  brain  in  the  state  of  images  or  memories.  They  wull  be  revived  more 
and  more  easily  vmder  the  influence  of  the  same  causes,  that  is  to  say,  the  same 
movements,  by  which  they  were  called  into  being.  Their  connexions  with 
tliese  movements  will  facilitate  them,  and  will  allow  in  the  long  run  of  the 
rapid  and  precise  performance  of  the  most  complicated  actions.  Thanks  to 
the  generally  cyclic  arrangement  of  the  nervous  system,  the  stimuli  originally 
received  by  it  find  in  it  numerous  echoes,  whose  duration  is  prolonged  there  in 
a  manner  which  wovild  not  be  suspected  at  first  sight  ;  at  the  same  time,  they 
confer  a  genuine  organization  on  tlie  stimuli,  using  the  word  in  the  dynamic 
sense  wliich  is  essential  in  the  case  of  the  living  being. 

7.  Exteriorization  of  the  sensation — The  sensations  arising  from 
impressions  made  on  the  skin,  sensations  which  physiological  analysis 
shows  us  to  be  dependent  on  the  integrity  of  a  determinate  region  of 
the  cerebral  cortex,  are  said  to  be  exteriorized,  that  is  to  say,  brought 
back  to  their  original  cause  which  has  acted  on  the  surface  of  the 
integument. 

The  exteriorization  of  sensation  is  a  fact  common  to  all  the  senses. 
It  is  evident  of  itself,  and  allows  of  no  really  satisfactory  rational 
explanation. 

Illusions  of  those  who  have  been  subject  to  amputation,  errors  of  exterioriza- 
tion.— Those  who  have  had  a  limb  amputated  have  often  a  persistent  sensation 


522 


SPECIAL    INNERVATIONS 


of  the  missing  member  (A.  Pare),  this  sensation  being  locaHzed  by  preference 
in  the  extremity  (fingers)  of  the  lost  segment,  which  seems  to  be  smaller  and 
approximating  to  the  cicatrix.  The  sensation  of  temperatvire  in  the  imaginary 
limb  varies  with  the  real  temperature  of  the  cicatrix.  Electricity  applied  to 
the  stump  exaggerates  these  sensations  and  renders  them  painful  (Weir- 
Mitchell)  ;  a  prick  on  the  cicatrix  is  localized  in  the  extreinity  of  the  amputated 
limb.  The  patient  frequently  executes  imaginary  movements  with  his  "  phan- 
tom limb,"  and  the  illusion  may  be  so  strong,  that  serious  falls  may  sometimes 
result  from  it.  These  illusions  which,  however,  gradually  diminish,  may  some- 
times last  for  years. 

These  sensations,  the  first  of  contact  (tactile),  the  second  of  movement 
(cinsesthetic),  have  all,  as  a  starting  point,  the  irritation  of  the  nerves  in  the 
cicatrix  of  the  stump,  which  irritation  is  inaccurately  exteriorized  by  the  con- 
sciousness. The  proof  of  this  is  that,  if  the  cicatrix  be  cocainised,  these  sensa- 
tions will  disappear  (after  a  short  period  of  exacerbation  at  the  instant  the 
prick  is  made),  to  reappear  after  the  elimination  of  the  drug  (Pitres). 

8.  Localization. — Not  only  are  tactile  sensations  exteriorized,  that 
is  to  say,  referred  by  the  consciousness  to  a  cause  external  to  the  body 
acting  on  its  surface,  but  we  can,  the  eyes  being  shut,  locate  them 
exactly  at  the  point  on  this  surface  where  the  cause  acts  ;  we  can  dis- 
tinguish between  impressions  made  on  one  or  other  limb,  one  or  other 


Fig  218. — The  cortical  motor  area  in  man  as  determined  by  the  researches  of  English 
and  American  surgeons.  Keen,  Mills,  Nancrede,  Horsley,  etc.  (copied  from  Dejerine). 

finger,  or  segment  of  these  parts.  This  distinction  has  its  origin  in 
the  fact  that  the  stimulation  affects,  in  these  various  localities,  different 
nervous  elements.  These  impressions  arrive  at  the  cerebral  cortex  in 
different  areas,  which  areas  reproduce  to  a  certain  extent  the  topo- 
graphy of  the  skin.  Doubtless  the  projection  from  the  skin  to  the 
cortex  is  not  direct  ;  the  initial  stimulation  is  made  on  a  network  ;  in 
the  spinal  cord  the  impulse  traverses  a  network  once  again  ;  the  cortex 


TACTILE    INNERVATION 


523 


itself  is  a  network  (not  vague  and  indefinite  as  was  formerly  thought, 
but  still  a  network).  In  spite  of  all  these  complications,  it  is  undeniable 
that  the  impulses  received  in  different  areas  undergo  a  localization 
which  is  prolonged  in  the  nervous  system  and  affects  the  consciousness 
in  various  ways.  The  proof  of  this  localization  is  easily  found,  but  its 
exact  formula  has  still  to  be  discovered.  It  allows  of  gradations  of 
whose  nature  we  are  ignorant.  To  deny  it  is  to  go  against  evidence, 
to  push  it  to  an  extreme  is  to  destroy  the  unity  of  the  ego.  It  is  marked 
by  contrasts  between  things  fundamentally  the  same.  It  has  for  a 
support  such  or  such  a  strongly  united  system,  which  on  this  account 
has  not,  however,  abandoned  all  connexion  with  other  systems.  A 
prick  on  the  finger  produces  a  sensation  locahzed  to  the  finger  ;  but, 
however  strong  this  sensation  may  be,  it  does  not  prevent  the  individual 
having  consciousness  of  the  rest  of  his  being,  and  this  is  why  the  linger 
is  distinguished  and  the  cause  of  the  sensation  localized  in  it. 


C.     TACTILE  AREA  FROM  A  MOTOR  POINT  OF  VIEW 
The  tactile  sensory  area  of  the  cerebral  cortex  receives  impulses 
coming  to  it  from  the  skin,  which  is  the  initial  organ  of  touch  ;  it  itself 


Fig.  2 19. — Cortical  motor  centres  of  the  ovirang-outang  (Simia  satyrus)    (after  Beevor 
and  Horsley.     Philos.  Trans.,  1890). 
Determination  of  the  cortical  areas   corresponding  to   tlie  principal  organs  of  movement. 
MI,  inferior  limb  ;    MS,  MS,  superior  limb  ;    tongue,  mouth,  eyelid  and  head  ;    special  areajor 
the  associated  movements  of  the  two  eyes. 

distributes  them  to  the  muscles  wMch  perform  those  varied  and  con- 
tingent movements  brought  into  being  by  our  external  relations. 
This  area  is,  as  we  have  already  observed,  motor  as  well  as  sensory  ;  it 
is  one  or  the  other  according  to  whether  it  is  receptive  of  the  impulses 


524  SPECIAL    INNERVATIONS 

which  come  to  it  from  without  through  the  grey  bulbo-meduUary 
axis,  or  whether,  conversely,  it  distributes  these  impulses  to  this  same 
grey  axis,  which  transmits  them  to  the  muscles  attached  to  the  different 
parts  of  the  skeleton.  It  is  therefore  both  a  guardian  and  also  a 
modifier  of  these  impulses,  which  have  already  been  profoundly  trans- 
formed and  retouched  before  reaching  it,  and  of  which  none  will  attain 
the  muscles  without  undergoing  fresh  transformations  and  fresh  re- 
touchings. 

The  destruction  of  this  area  involves  a  paralysis  of  the  muscles  of 
the  skeleton  ;  its  stimulation  causes  these  muscles  to  become  func- 
tionally active.  The  paralysis  thus  produced  is  not  absolute  as  in  the 
case  of  section  of  the  anterior  roots,  when  all  motricity  becomes  im- 
possible ;  it  affects  certain  modalities  of  movement,  which  will  be 
suppressed,  while  others  will  persist  ;  all  movement  preceded  by  a 
mental  representation  of  the  act  to  be  performed  will  have  disappeared. 
The  stimulus  will  no  longer  produce  the  abortive  contraction  obtained 
by  acting  on  the  roots,  but  will  arouse  a  co-ordinated  muscular  effort 
appropriate  to  a  particular  end.  Distinctions  of  the  same  kind  have 
been  made,  from  the  sensory  point  of  view,  between  the  tactile  area 
and  the  posterior  roots  ;   they  are  essential. 

A.  Limitation. — From  the  point  of  view  of  movement  even  more 
than  from  that  of  sensibility,  the  tactile  area  is  confined  to  a  limited 
territory  on  the  surface  of  the  cortex.  This  area  occupies  the  region 
called  Rolandic,  formed  by  the  central  convolutions,  namely  :  the 
ascending  jroyital,  the  ascending  parietal,  and  the  paracentral  lohide, which. 
is  a  prolongation  of  the  last-named  on  the  mesial  surface  of  the  cerebral 
hemisphere  ;  it  slightly  encroaches  on  the  portions  which  are  nearest 
to  the  frontal  or  parietal  convolutions. 

Divisions. — In  the  brain  itself,  and  including  its  surface,  something 
of  the  same  metameric  disposition  which  has  been  noticed  with  regard 
to  the  roots  of  the  spinal  cord  may  be  observed.  Primarily,  the 
Rolandic  region  is  divisible  into  four  large  areas  which  correspond  to 
the  inferior  limb,  to  the  trunk,  to  the  superior  limb,  to  the  larynx,  and 
to  the  head.  These  areas  succeed  each  other  in  the  order  just  indicated  ; 
they  are  arranged  in  stages  alongside  the  fissure  of  Rolando,  from  its 
superior  to  its  inferior  extremity,  extending  as  far  as  the  vicinity  of 
the  fissure  of  Sylvius. 

There  is,  then,  on  the  surface  of  the  brain  a  supero-posterior  region 
which  corresponds  to  the  abdominal  member,  a  supero-anterior  corre- 
sponding to  the  trunk,  a  median  region  corresponding  to  the  thoracic 
limb,  and  an  inferior  region  answering  to  the  head  and  to  the  larynx. 

Subdivisions. — Each  of  these  regions  is  subdivided  in  the  same  way 


TACTILE    INNERVATION  525 

as  the  segments  of  the  parts  with  which  it  is  in  functional  relationship. 
This  division  is  most  marked  as  regards  the  limbs  and  the  head,  these 
being  made  up  of  organs  which  are,  functionally,  more  differentiated 
than  the  trunk.  Quite  at  the  superior  limit  of  the  fissure  of  Rolando, 
a  cortical  area  exists  which  is  functionally  connected  with  the  great 
toe  ;  immediately  beneath  it  is  another  area  allied  to  the  foot  and  the 
other  toes,  then  to  the  leg,  the  thigh,  the  knee.  The  median  region 
may  be  divided  into  consecutive  areas  functionally  related  to  the 
shoulder,  the  arm,  the  hand  and  the  fingers  ;  the  thumb,  on  account 
of  its  great  importance,  has  a  special  area  situated  in  the  inferior 
portion  of  the  ascending  parietal. 

Between  the  inferior  extremity  of  the  fissure  of  Rolando  and  the 
fissure  of  Sylvius  are  located  in  graduated  stages  the  areas  of  the  face, 
the  tongue,  the  pharynx  and  of  the  upper  jaw.  That  of  the  larynx 
is  at  the  inferior  extremity  of  the  ascending  frontal,  in  the  immediate 
neighbourhood  of  the  so-called  motor-centre  of  speech  situated  at  the 
base  of  the  third  frontal  convolution. 

Nape  of  the  neck  and  trunk. — The  determination  of  the  motor  areas 
of  the  nape  of  the  neck  and  of  the  trunk  has  given  rise  to  many  investi- 
gations and  discussions.  From  the  clinical  standpoint  there  is  not 
much  evidence  on  this  matter  because  hemiplegic  patients  are  kept 
immobile  in  the  recumbent  attitude,  and  the  paralysis  of  these  parts 
attracts  no  attention,  and,  indeed,  is  not  usually  sought  for.  Munck, 
and  later  Grosglick  and  Rothmann,  located  these  motor  areas  in  the 
marginal  convolution  (first  frontal),  consequently  in  front  of  the  pre- 
central  or  pre-Rolandic  sulcus  which  separates  it  from  the  ascending 
frontal.  It  is  also  very  much  on  the  faith  of  physiological  experiments 
that  a  centre  for  the  conjugated  deviation  of  the  eyes  is  maintained  by 
certain  authors  to  exist,  this  centre  being  situated  below  the  preceding, 
in  the  frontal  lobe.  These  results  are  based  on  ablations  and,  more 
particularly,  on  stimulation  of  these  different  areas,  principally  on  the 
brain  of  the  monkey. 

B.  Stimulation. — Artificial  stimulation  of  the  cerebral  cortex  gives 
rise  to  an  impulse  which,  after  leaving  the  latter,  is  conveyed  to  the 
muscles  and  passes  through  numerous  halting  places.  The  first  of  these 
is  the  cortex  itself,  and  the  question  arises  as  to  whether  it  modifies 
the  impulse,  or  whether  the  latter  only  traverses  it  in  order  to  proceed 
to  the  subjacent  white  matter.  This  matter  is  itself  excitable  ;  it 
contains  the  fibres  of  projection  which  descend  from  the  cortex  to  the 
basal,  bulbar  and  medullary  centres  which  are  more  or  less  immediately 
connected  with  the  muscles.  And  being  such,  it  also  presents  func- 
tional localization  recalling  more  or  less  nearly  those  of  the  cortex  itself. 


526  SPECIAL    INNERVATIONS 

Excitability  of  the  white  cerebral  matter. — Formerly  the  white  matter  of  the 
brain  was  recognized  as  being  as  inexcitable  artificially  as  the  cortex  itself.  Bur- 
don-Sanderson,  Carville,  Diu'et  and  many  other  observers  found  that  it  responded 
to  stimvili,  as  did  the  grey  matter  covering  it  in  the  localities  where  this  latter 
is  excitable  (motor  area),  and  that  it  gave  rise  to  reactional  manifestations  of 
the  same  nature.  Frangois-Franck  and  Pitres  undertook  a  comparative  study 
of  the  motor  reactions  of  the  two  substances.     Here  are  the  results  : — 

Comparison  between  the  excitability  of  the  grey  and  the  white  matter. — Tlie 
grey  is  more  excitable  than  the  ivhite  tnatter  which  lies  immediately  beneath  the 
cortex  ;  with  an  ecjual  intensity  of  stimulation  the  motor  reaction  is  stronger 
in  the  first  than  in  the  second.  The  gi'ey  niatter,  even  in  the  case  of  artificial 
stimvilation,  would  thus  possess  a  power  of  organizing  the  impulses  which  does 
not  appertain  to  the  white  matter. 

The  grey  matter  impresses  on  the  impulses  traversing  it  a  sensible  delay, 
which  notably  prolongs  the  latent  period  intervening  between  the  moment  of 
stimulation  and  the  resulting  motor  effect.  This  delay,  which  is  6  J  hvmdredths 
of  a  second  for  a  cortical  stimulation,  falls  to  4J  hundredths  of  a  second  for 
stimulation  of  the  corona  radiata.  It  must  be  observed  that  the  total  delay 
in  both  instances  is  much  longer  than  in  the  case  of  stimulation  of  a  motor 
nerve,  the  latter  being  of  the  same  length  as  the  course  to  be  traversed,  about 
four  tunes  greater.  The  reason  is  that  the  impulse  in  this  course  must,  as  has 
already  been  observed,  pass  through  other  relays,  which  retard  it  on  their  own 
account  ;  the  delay  is  mvich  greater  as  regards  direct  movements  than  for  those 
which  are  crossed. 

The  tetanus  resulting  from  cortical  stimulation  has  a  certain  tendency  to 
persist  after  the  stimulation  has  ceased,  this  tendency  being  much  gi'eater  than 
in  the  case  of  tetanus  due  to  stimulation  of  the  corona  radiata.  If  exaggerated, 
this  tendency  to  persistence  of  the  motor  effect  will  become  that  form  of  epilepsy 
which  is  provoked  by  excitation  of  the  cortex  and  of  the  cortex  alone. 

Stimulation  of  the  corona  radiata  has  different  motor  effects  (but  only  as 
regards  intensity)  when  approaching  the  internal  capsule.  This  is  obviously 
due  to  the  greater  density  of  the  conducting  paths,  in  proportion  as  the  dis- 
tance from  the  cortex  is  increased,  on  account  of  the  fan  or  cone-shaped 
(base  uppermost)  form  of  the  motor  area  in  the  brain. 

Variations  of  the  excitability  of  the  cortex  ;  its  conditions.^ — Many  toxic  agents 
modify  the  excitability  of  tlie  cerebral  cortex.  The  anaesthetics  must  be  men- 
tioned first  :  chloroform,  ether  (Hitzig),  chloral  (Richet),  morphine  (Bubnoff 
and  Heidenhain)  have  a  truly  elective  action  on  the  cortical  layer,  whose  ex- 
citability they  abolish,  while  that  of  the  white  sub-cortical  tracts  still  persists. 
Local  refrigeration  acts  in  the  same  manner  as  also  do  cocaine  (Carvalho)  and 
bromide  of  potassium,  which  exert  more  general  effects  ;  essence  of  absinthe 
paralyses  the  brain  and  allows  of  the  persistence  of  the  reflex  power  of  the 
subjacent  centres,  to  which  the  convulsions  produced  by  this  poison  bear 
witness  (FranQois-Franck). 

On  the  contrary,  strychnine  increases  the  cortical  excitability  ;  local  inflam- 
mation of  the  surface  of  the  brain  develops  it  to  its  highest  point.  Anaemia 
of  the  brain,  according  to  its  phases,  first  augments  and  afterwards  destroys  it. 

1.  Delimitation  of  the  motor  areas  by  stimulation. — Stimulation  of 
the  cerebral  cortex  has  been  practised  on  all  animals,  from  the  batra- 
chia  up  to  the  monkey,  and  even  on  man  himself.  It  is  this  excita- 
tion which,  when  methodically  applied,  enables  us  to  define  an  area  in 
the  cortex  which  is  related  to  external  visible  movements  and  is  situ- 


TACTILE    INNERVATION 


527 


ated  in  the  midst  of  areas  called  inexcitable,  because  their  stimulation 
causes  no  appreciable  external  manifestation.  This  motor  or  excitable 
region  is  divided    and    subdivided  into  areas  which    are  sometimes 


Fig.  220. — Fibres  of  pro- 
jection of  the  cortex, 
their  course,  and  rela- 
tive situation  in  tlae 
cortex  (upper  fig.),  in 
the  thalamic  and  sub- 
thalamic regions  of  the 
internal  capsule  (the 
two  middle  figs.),  in 
the  cms  cerebri  (lower 
fig.).  Cortex  is  divided 
into  tliree  sectors  (an- 
t  e  r  i  o  r,  posterior, 
middle). 

The  anterior  or  frontal 
sector  of  the  cortex  sends  its 
fibres  into  the  anterior  seg- 
ment (Cia)  of  the  internal 
capsule  and  the  anterior 
portion  of  the  optic  thal- 
amus {Th).  The  posterior 
or  occipito-parietal  sector 
sends  its  fibres  into  the  re- 
trolenticular  {Cirl)  and  sub- 
lenticular segment  {Cisl)  of 
tlie  internal  capsule  ;  the 
pulvinar  (Pul),  the  external 
geniculate  bodj'  {Cge),  and 
the  anterior  corpus  quadri- 
geminum  (Cla)  receive  those 
of  the  occipital  lobe  ;  the 
posterior  portion  of  the 
external  nucleus  of  the 
thalamus  and  the  red  nucleus 
(NR)  receive  those  of  the 
parietal  lobe. 

The  middle  sector  of  the 
cortex  sends  its  fibres  into 
the  knee  and  the  posterior 
segment  of  the  internal 
capsule  with  radiations  into 
the  optic  thalamus  and  forms 
by  its  fibres  alone  the  crusta 
(pied)  of  the  crus  cerebri. 
This  middle  sector  comprises 
an  inferior  temporal  or  sub- 
syUdan  segment  and  a 
superior  fronto-parietal  or 
supra-sylvian  segment.  The 
sub-sylvian  segment  sends 
its  fibres  into  the  sub-lenti- 
cular segment  {Cisl)  of  the 
internal  capsule  with  radia- 
tions into  the  internal  geni- 
culate  body    [Cgi]    and    the 

ventral  region  of  the  thalamvLS  :  it  forms  the  posterior  sixth  of  the  posterior  segment  of 
the  internal  capsule  and  tlae  external  sixth  of  the  crusta  of  the  crus  cerebri  or  column  of  Tiirck 
(FT).  The  supra-syhian  or  superior  segment  sends  its  fibres  into  the  knee  and  the  posterior 
segment  of  the  internal  capsule  (thalamic  region),  then  into  the  anterior  five-sixths  of  the 
sub-thalamic  region  and  into  the  internal  four-fifths  of  the  crusta  of  the  crus  cerebri  (after 
Dejerine). 


528  SPECIAL    INNERVATIONS 

extremely  small  and  which  correspond  in  an  isolated  manner  to  distinct 
muscular  regions,  as  well  as  to  special  and  adapted  movements,  recall- 
ing those  which  the  animal  is  seen  to  execute  in  the  exercise  of  its 
voluntary  motor  functions.  These  subdivisions  of  the  motor  area, 
which  are  further  superposed  to  similar  subdivisions  of  the  cutaneous 
sensibility,  are  numerous  in  proportion  to  the  elevation  in  the  series 
of  the  animal  on  which  the  experiment  is  made. 

Another  reason  why  the  results  obtained  througli  stimulation  of  the  cortex 
in  the  monkey  are  of  great  value  is  that  the  homology  of  the  furrows  and  con- 
volutions between  its  brain  and  that  of  man  is  relatively  easy  to  trace,  while 
the  type  of  brain  in  the  carnivora  is  considerably  different  from  our  own.  It 
is  stimulation  of  the  cortex  in  the  monkey  which  has  so  far  yielded  the  most 
definite  results  concerning  cerebral  motor  localization.  The  relative  ^Dosition 
of  the  cortical  areas  possessing  a  differentiated  motor  function  has  been  con- 
sidered above,  and  in  part  according  to  the  information  fiirnished  by  these 
stimulations.  It  only  remains  to  complete  this  information  on  several  details 
as  follows  : — 

Cerebral  metamerism. — The  motor  tactile  area  may  be  rej^resented  as  a 
projection  of  the  muscular  system  on  the  cortex  of  the  brain  ;  nevertheless, 
the  arrangement  of  the  differentiated  areas  constituting  it  is  not  thereby  meta- 
meric,  but  is  also  governed  by  functional  relations.  It  may  be  observed  that, 
for  a  given  limb  the  most  powerful  articulation,  as  the  thigh  and  the  shoulder, 
is  located  in  front  ;  the  smaller  articulations  and  those  more  differentiated  as 
regards  movement  (great  and  small  toes,  thumb  and  fingers)  are  located 
posteriorly. 

In  the  area  corresponding  to  the  movements  of  a  given  articulation,  the 
stimulus  selects  those  centres  which  corresj^ond  to  its  principal  movements, 
such  as  extension  or  flexion.  The  fu'st,  representing  less  differentiated  move- 
ments, are  in  front,  the  others  behind. 

Indeterminate  boundaries  ;  gradual  passage  from  one  cortical  area 
to  another. — These  motor  areas,  however  restricted  they  may  be,  have 
not,  between  themselves,  continuous  and  fixed  limits  which  would 
render  it  impossible  to  leave  one  without  passing  into  another  and 
bringing  its  special  effects  into  action.  On  the  contrary,  in  each  of 
them  there  is  a  central  point  whose  stimulation  gives  the  maximum 
motor  effect,  a  point  starting  from  which  the  effects  of  the  stimulus 
continue  to  diminish,  to  disappear,  to  be  modified  and  to  change  direc- 
tion, when  the  stimulus  begins  to  penetrate  into  one  of  the  neighbouring 
motor  areas.  The  term  "  centre,"  often  applied  to  these  areas,  here 
retains  something  of  its  etymological  meaning. 

2.  Character  of  the  movements. — The  movements  which  are  caused 
by  stimulation  of  the  cerebral  cortex  are  easily  distinguishable  from 
those  which  may  be  provoked  by  stimulation  of  the  other  parts  of  the 
nervous  system  ;  they  display  in  an  eminent  degree  the  character  of 
co-ordinated  and  adapted  movements.  This  character  will  be  most 
apparent  if    it  is  compared  with  that  of  the  movements  evoked  by 


TACTILE  INNERVATION 


529 


stimulation  of  the  motor  nerve  roots,  or  of  the  spinal  cord.     If,  for 
instance,  the  motor  nerves  of  a  limb  are  stimulated,  movement  arises 


.-'^      MvU-of    Ft> 


<"/ 


the  Alice     JJrln.  of  ;  ^--^^^ 

the  hip  ;  ^~v^ 

IjEG    (ijUttxu)i       MvU.of   "~~-,^^ 

/     the  jifh-ig,  ^"^V^ 

TRUNK 'iK^f- 

of  the   1°/""=  , 


Fig.   221. — The  motor   centres  of   the  Macacus  sinicus   (after  Horsley  and   Schaffer.. 

Philos.  Trans.,  1887). 
Upper  fig.,  external  surface  of  the  brain.     Lower  fig.,  mesial  siirface. 
F,  frontal  lobe  ;    P,  parietal  lobe  ;    O,  occipital  lobe  ;    T,  temporal  lobe. 

in  the  latter  suddenly,  but  the  limb  is  immediately  fixed  in  a  rigid 
position,  becoming  motionless  through  the  tetanic  efforts  of  antagon- 
istic muscles,  its  position  being  given  to  it  by  the  most  powerful  of 
them  :  when  the  stimulus  ceases,  this  rigidity  also  suddenly  yields. 
Stimulation  of  the  motor  area  of  a  limb  has  very  different  effects  : 
instead  of  the  impulsive  simultaneousness  which  follows  stimulation 

P-  MM 


530 


SPECIAL  INNERVATIONS 


of  the  spinal  cord  or  of  its  nerve  roots,  the  muscles  of  the  limb  present 
a  continuous  succession  of  positio7is,  passing,  for  example,  from  flexion 
to  extension  or  reciprocally,  by  delineating  a  definite  movement,  of  the 
same  voluntary  nature  as  those  which  are  controlled  by  the  will. 

Primary  and  secondary  movements. — The  duration  of  the  stimulation 
is  an  important  factor  in  the  question  ;  however  short  a  time  it  lasts, 
new  motor  phenomena  will  be  added  to  the  initial  movements.  Hence 
a  distinction  has  been  made  between  primary  movements  (those  which 
are  first  produced,  and  are  in  some  way  directly  related  to  the  point 
stimulated),  and  secondary  movements  (being  those  which  only  appear 
after  a  time,  and  in  segments  removed  successively  from  that  corre- 
sponding to  the  stimulated  spot).  From  the  spot  receiving  the  stimulus 
the  latter  seems  to  propagate  itself  little  by  little  (by  physiological 


Retraction  of  the  corner  «/' 
the  tnoiuh  of  the  opposite  siUe 


Compression  of  the  lips 

Opening  of  the  month 

Pouting 


.   Contraction  of  the 
ysuperinr  half  of  the 
orbiciitnris  oris  of  the 
opposite  side 


^si'i,/  of  the  et/eiids,  ynorc 
narked  ou  the  opposite  side 


Fig.  222. — Cortical    motor  centres  of    the  orang-outang  [Simia  satyrus)  (after  Beevor 
and  Horsley,  Philos.  Trans.,  1890). 

Precise  location  of  the  movements  of  the  principal  segments  (Wp,  shoulder,  elbow,  wrist, 
fingers,  thumb,  forefinger,  etc.).  Co-ordinate  or  expressive  movements  especially  of  the  head 
^eyes,  eyehds,  lips,  mouth,  etc.). 

paths)  to  the  neighbouring  regions  of  the  cortex,  whose  functional 
activities  are  thus  involved  by  it.  This  concatenation  is  not  arranged 
haphazard,  but  is,  on  the  contrary,  harmonious,  and  somewhat  striking 
motor  acts  may  result  from  it  :  extension  of  the  arm  and  hand  to  reach 
an  object  (ascending  frontal  at  the  origin  of  the  first  frontal) ;  flexion 
and  supination  of  the  forearm  with  elevation  of  the  hand  to  the  mouth 
(middle  third  of  the  ascending  frontal  towards  the  knee  of  the  pre- 
central  fissure) ;  closing  of  the  fist  (middle  third  of  the  ascending  pari- 
etal) ;  movements  of  the  posterior  limb  adapted  to  seize  an  object 
with  the  foot,  or,  again,  to  scratch  the  chest  or  the  abdomen  (superior 
portion  of  the  frontal  and  of  the  ascending  parietal)  ;   opening  of  the 


TACTILE  INNERVATION 


531 


mouth  with  protrusion  and  retraction  of  the  tongue  (inferior  extremity 
of  the  ascending  frontal)  ;  rhythmical  movements  of  mastication  (the 
same  locality  a  little  farther  forward)  ;  movements  of  swallowing 
{same  locality,  still  farther  forward). 

The  inferior  portion  of  the  ascending  frontal  contains,  further,  the 
motor  area  for  adduction  of  the  vocal  cords  of  the  larynx.  In  the  dog 
this  area  is  situated  in  the  anterior  region  of  the  sigmoid  gyrus  (over 
the  isthmus  of  the  so-called  pre-crucial  or  pre-frontal  gyrus)  ;  it  is 
thus  in  the  immediate  neighbourhood  of  the  centre  for  the  pharynx 
(that  of  which  the  vohmtary  exercise  induces  the  automatic  movement 
of  swallowing),  and  is  also  in  a  sense  included  in  the  general  area  of 
the  muscles  of  the  neck  and  of  the  trunk  (Munck).  The  bilateral  abla- 
tion of  the  centre  of  the  larynx  suppresses  the  emission  of    sounds 


Fig.  223. — Sensori-motor  areas  of  the  cerebral  cortex  of  the  Macacus  sinicus  (after 
Beevor  and  Horsley,  Philos.  Trans.,  1890). 

Determination  of  the  cortical  areas  corresponding  to  the  principal  regions  of  the  body  or 
segments  of  the  Umbs.  Indication  of  the  movements  aroused  by  stimulation  of  certain  of  these 
areas,  especially  as  regards  tlie  muscles  of  the  head  (eyes,  eyeUds,  mouth,  jaw). 

(barking),  and  only  allows  of  the  persistence  of  some  feeble  cries  like 
those  of  a  new-born  animal.  It  is  followed  by  a  secondary  degeneration 
of  slight  extent,  but  still  recognizable,  in  the  crura  cerebri  (and  also 
in  the  peduncle  of  the  mamillary  body  of  the  same  side)  ;  hence 
there  must  be  fibres  of  projection  which  extend  from  this  area  to  the 
medulla  oblongata. 

3.  Motor  centre  of  language. — In  man  the  posterior  portion  of  the 
third  frontal  contiguous  to  the  inferior  extremity  of  the  ascending 
frontal  convolution  (convolution  of  Broca)  contains  an  area  of  extreme 
importance,  that  which  is  named  the  motor  area  of  speech.     It  answers 


532 


SPECIAL  INNERVATIONS 


to  what  is  called  a  centre  of  association,  and,  in  so  far  as  the  expression 
of  the  instincts  in  animals  can  be  equivalent  to  the  language  of  man, 
it  has  also  its  counterpart  in  them.  In  the  dog,  the  motor  area  of 
barking  is  situated,  according  to  Ferrier,  at  the  point  of  anterior  union 
of  the  third  and  fourth  external  convolution.  Stimulation  of  this 
region  causes,  according  to  this  author,  a  co-ordinated  assemblage  of 
movements,  giving  rise  to  vocal  sounds,  attempts  at  barking,  also 
indeed  to  a  distinct  bark  ;  in  this  Bechterew  agrees.  Duret  has  also 
obtained  similar  results.  The  preceding  area  has  by  him  been  identified 
with  the  convolution  of  Broca,  by  comparing  the  distribution  of  the 
arteries  in  man  and  animals.  The  removal  of  this  area  in  a  dog  sup- 
pressed barking  for  two  months,  and  the  animal,  like  a  man  who  has 
become  aphemic,  was  forced  to  undergo  a  second  apprenticeship  in 
order  to  regain  his  lost  vocal  function. 

Duret,  by  lightly  compressing  this  area,  has  also  been  able  to  pro- 
voke distinct  barking.  The  stimulation  due  to  the  compression  is  no 
doubt  caused  by  the  temporary  anaemia  following  the  effacement  of 
its  vessels. 

The  grey  medullary  axis  and  the  cerebral  cortex. — Stimulation  of  a  portion  of 
the  cortex  may  thus  bring  into  i)lay  a  co-ordinated  system  of  nerves  and  of 
mviscles,  so  as  to  elicit  complex  and  definite  acts.  Where  is  the  co-ordination 
effected  ?     In  what  locality  of  the  grey  matter  ?      Obviously  the  spinal  cord 


Fig.  224. — The  excitable  regioji  of  tlie  internal  capsule  of  the  Macacus  sinicus  (after 
Beevor  and  Horsley,  Phil.  Trans.,  1890. 

Eight  sections  of  the  capsule  arranged  in  stages  from  above  downwards,  showing  the  site' 
and  the  boundaries  of  its  excitable  area.  This,  at  first  very  extensive,  becomes  restricted,^at 
first  to  its  anterior  portion,  is  again  increased  in  this  direction,  once  again  restricted,  and  ends 
by  occupying  at  its  inferior  portion  (svib-thalamic)  merely  the  knee  and  part   of   its    posterior 


takes  one  share  in  it  and  the  cerebral  cortex  another.  In  movement  called 
primary  (movement  limited  to  a  segment  of  a  limb  and  directly  dejoendent  on 
the  stimulated  spot,  therefoi-e  restricted  and  in  a  sense  elementary)  it  seems  as 
if  it  were  especially  the  grey  matter  of  the  spinal  cord  which  takes  part  in  regu- 
lating the  motor  neurons,  and  by  them  the  muscles  executive  of  this  movement. 
But  when  the  neighboviring  segments  participate  in  the  movement,  by  giving 
it  a  more  and  more  complicated  form,  it  must  be  admitted  that  the  cortex  in 
its  turn  takes  its  share  in  co-ordinating  these  different  systems  and  elementarj; 


TACTILE  INNERVATION 


533 


movements  into  a  motor  act  of  a  more  complex  adaptation.  Localized  in  a 
limited  area  of  the  cortex,  the  stimulus  invades  the  motor  field  in  two  principal 
dii'ections.  It  extends  in  depth  so  as  to  reach  in  the  first  instance  the  muscles 
wliich  are  in  the  most  direct  relationship  with  the  excited  area.  Further,  it 
extends  laterally,  bringing  into  action  new  regions  of  the  cortex,  Avhich, 
secondarily,  send  impulses  to  the  muscles  with  which  they  are  in  connexion. 
The  conflicts  of  these  impulses,  which  are  at  the  same  time  both  motor  and 
inhibitory,  determine  the  direction  and  the  particular  form  of  the  movement. 
But,  on  the  other  hand,  when  localized  in  a  limited  area  of  the  corona  radiata 
or  of  the  internal  capsule, 

the      stimulus      extends  collat.  C.  call. 

only  in  dejjth,  following 
tlie  course  of  the  fibres 
excited,  and  finds  pos- 
sible associations  in  the 
grey  subcortical  masses 
in  which  tliese  fibres 
end  ;  whence  arises  the 
difference  in  certain 
cases  between  the  effect 
of  stimulation  of  the  cor- 
tex or  of  the  fibres  of 
projection. 

Corpus  callosum. — The 
part  played  by  the  cor- 
pus callosum  and,  in 
fact,  that  played  by  all 
the  other  inter-hemi- 
spherical commissures, 
is  far  from  being  understood.  In  principle  it  is  admitted  that  the  coi'pus 
callosiun  associates  the  functions  of  the  two  hemispheres  for  the  performance 
of  bilateral  actions.  According  to  Cajal,  the  same  neuron  (a  pyramidal  cell), 
which  gathers  together  the  impulses  in  the  corresponding  hemisphere,  distri- 
butes these  not  only  bj^  the  descending  fibres  jDroceeding  from  it,  but  also 
by  the  collaterals  which,  arising  from  the  axis  cylinder  near  to  the  cell,  dis- 
tribute them  partially  to  the  opposite  hemisphere,  by  following  tlie  route  of 
the  corpus  callosum  ;  whence  the  solidarity  which  is  established  between  the 
motor  elements  of  the  two  sides  by  this  transmission  of  the  impulse  from  one 
to  the  other. 

Mott,  by  stimulating -^he  corpus  callosum,  has  obtained  bilateral  movements 
of  the  head,  the  eyes,  the  fingers,  the  shoulder,  the  trunk,  the  leg,  and  the  pelvis, 
but  not  of  the  face.  If,  after  the  removal  of  one  hemisphere  or  of  the  motor 
area,  the  longitudinal  section  of  the  corpus  callosum  is  stimulated,  the  move- 
ments are  vmilateral. 

Muratoff  has  observed  that  section  of  the  corpus  callosmn  was  followed  by 
]3aralytic  symptoms  similar  to  those  arising  from  destruction  of  the  motor  area. 
But  other  observers  (Koranyi,  Lo  Monaco)  have  denied  the  occurrence  of  these 
effects.  It  may  be  understood  that,  strictly  speaking,  section  of  this  com- 
missure is  not  attended  wdth  any  very  apparent  paralysis,  while  stimulation 
causes  positive  effects  revealed  by  movements.  The  same  may  be  said  with 
regard  to  experiments  carried  out  on  the  motor  area  itself. 

Co-ordinated  sensori-motor  systems. — The  co-ordinated  action  of 
muscular  movement  is  therefore  of  two  degrees.     In  the  first  degree 


f  Ant.  cunimiis. 


Pyr.  fibre 

-The  components  of  the  corpus  callosiun  and 
the  anterior  commissure. 

Diagram  of  a  transverse  section  of  the  brain  (aftrr  Cajal). 


534  SPECIAL  INNERVATIONS 

this  co-ordination  acts  in  the  inferior  systems,  of  which  the  spinal  cord 
is  the  keystone  ;  above  this,  in  a  second  degree,  it  operates  in  the 
superior  systems,  of  which  the  cerebral  cortex,  in  its  turn,  forms  the 
most  differentiated  portion.  A  very  interesting  experiment  of  Toma- 
sini  enables  us  to  obtain  a  glimpse  of  the  mechanism  of  this  co-ordina- 
tion. 

Experiment. — Before  stimulating  the  motor  area  of  a  limb,  the 
posterior  roots  of  this  limb  are  uncovered  and  cut.  Thus  the  effects 
of  the  excitability  of  the  cortex  are  profoundly  modified.  The  excita- 
bility seems  changed  :  it  undergoes  a  first  phase  of  exaltation,  then  a 
second  one  of  depression  ;  but,  what  is  most  important,  the  movements 
which  were  co-ordinated  become  inco-ordinated. 

At  first  sight  it  seeins  as  if  the  posterior  roots  have  nothing  to  do  with  the 
apparently  j^urely  motor  phenomenon  resuking  from  stimnlation  of  the  cortex. 
But,  in  reahty,  they  jJartly  contribute  to  give  to  it  its  essential  character.  In 
fact,  it  is  not  sufficient  that  the  grey  medullary  matter  remains  in  its  place  for 
the  co-ordination  to  be  effeci:ed  ;  it  is  also  necessary  that  it  should  have  pre- 
served the  connexions  by  means  of  which  it  obtains  information  concerning 
the  movement  which  it  itself  produces.  The  impulse,  after  its  descent  from 
the  brain,  falls  into  a  cyclic  system,  in  which  it  circulates  in  the  true  sense  of 
the  word.  This  circulation,  once  interrupted,  there  is  no  longer  any  association 
between  sensibility  and  movement,  and  therefore  no  more  possible  co-ordination. 
It  is  necessary,  in  fact,  for  the  imptilse  to  reascend  to  the  spinal  cord,  and  even 
to  the  brain,  from  the  contracted  muscles  ;  by  cutting  the  sensory  roots,  the 
ascending  paths  are  interrupted,  and  the  cyclic  spino-muscular  and  also  the 
cortico-muscular  system  are  broken,  whence  arises  the  ataxy  of  movement 
observed  by  all  those  who  have  performed  this  section  of  the  posterior  roots 
in  animals  which  have  afterwards  been  left  to  themselves. 

4.  Direct  and  crossed  action. — It  has  long  been  known  that  a  lesion 
attacking  one  of  the  two  cerebral  hemispheres  is  revealed  by  a  paralysis 
of  the  muscles  of  the  opposite  side  of  the  body,  and  anatomy  has  pointed 
out,  in  addition  to  the  decussation  of  the  bulbar  pyramids,  that  there 
are  other  numerous  paths  in  which  the  conducting  fibres  cross,  and 
this  may  explain  the  occurrence  of  the  hemiplegia.  This  simple  state- 
ment also  requires  important  corrections.  It  was  suggested  by  the 
observation  of  hemiplegics,  in  whom  paralysis  attacks  (on  the  opposite 
side  to  the  cerebral  lesion)  portions  of  the  body  which  are  immediately 
obvious,  such  as  the  face  and  the  limbs.  The  features  are  twisted, 
the  loss  of  power  in  the  limbs  may  be  complete  (the  arm  being  a  more 
differentiated  organ  is  generally  more  paralysed  than  the  leg). 

Paralysis  does  not,  however,  respect  the  side  which  is  supposed  to 
be  immune,  because  this  side  is  obviously  weakened,  and  may  even 
be  the  seat  of  paresis  ;  but  the  difference  of  power  between  the  two 
sides  is  so  great  that  this  weakening  is  often  unnoticed. 


TACTILE  INNERVATION  535 

Thus  the  hemisjphere  of  one  side  in  reality  governs  the  muscles  of  both 
sides,  hut  generally  very  unequally,  and  much  more  those  of  the  opposite 
side  :  its  action  is  what  is  called  bilateral.  It  is  quite  the  exception 
for  this  action  to  be  distinctly  unilateral.  But  this  bilateral  quality 
allows  of  gradations,  and  at  the  same  time  of  variety  in  form.  There 
are  muscles  as  regards  which  the  action  of  a  hemisphere  is  distinctly 
bilateral,  that  is  to  say,  equal  on  both  sides  of  the  body,  as,  for  example, 
the  muscles  of  the  nape  of  the  neck  and  of  the  trunk,  and,  above  all,  of 
the  vocal  cords. 

Movements  of  the  eyes. — The  action  of  a  single  hemisphere  on  the 
movements  of  the  eyes  is  bilateral,  in  the  sense  that  it  is  exercised 
simultaneously  on  the  muscles  belonging  the  one  to  the  eye  of  the  one 
side,  and  the  other  to  that  of  the  other  side  ;  but,  the  parallelism  of 
the  visual  axis  necessary  for  distinct  vision  being  granted,  the  co- 
operating muscles  which  are  controlled  by  one  hemisphere  are  the 
external  rectus  of  the  opposed  side  and  the  internal  rectus  of  the  same 
side  ;    that  is  to  say,  they  are  unsymmetrical  muscles. 

But  there  are  also  contractions  of  the  symmetrical  muscles  of  the 
eyes  which  govern  their  movements  of  convergence,  which  is  another 
very  important  function  of  these  muscles  in  the  association  of  the  two 
eyes  for  binocular  vision. 

Movements  of  the  tongue. — The  tongue,  which  is  an  apparently 
median  and  single  organ,  presents  movements  responding  to  various 
functions  and  which,  to  a  certain  degree,  are  analogous  to  those  of  the 
eyes.  Some  of  them  are  the  result  of  muscular  symmetrical  actions, 
such  as  the  protrusion  of  the  tongue  or  its  retraction  within  the 
mouth,  and  are  provoked  by  the  excitation  of  a  single  hemisphere. 
These  are  those  Avhich  are  called  bilateral,  that  is  to  say,  which  are 
bilaterally  represented  in  each  hemisphere.  There  are  others,  the 
result  of  muscular  actions  which  are  indeed  bilateral,  but  no  longer 
symmetrical  ;  such, -for  instance,  is  the  twdsting  of  the  tongue  to  the 
right,  which  is  produced  by  a  combined  action  of  the  protrusor  muscle 
(genio-hyoid)  on  the  right  side,  and  of  the  retractor  muscle  (lingual) 
on  the  left,  which  is  obtained  by  the  stimulation  of  a  single  hemisphere 
in  a  slightly  different  point  from  that  which  produces  the  preceding 
movement.  In  this  lateral  movement,  which  recalls  the  conjugated 
deviation  of  the  eyes,  the  retractor  muscle  is  the  equivalent  of  the 
external  rectus  of  one  side  and  the  propulsor  of  the  internal  rectus, 
of  the  opposite  side. 

In  order  to  dissociate  experimentally  these  two  opposite  actions, 
which  terminate  in  a  lateral  movement,  it  is  necessary  to  separate  the 
two  halves  of  the  tongue  by  a  median  longitudinal  section  (Horsley 


536  SPECIAL  INNERVATIONS 

and  Beevor)  ;  it  will  be  seen  that,  at  the  moment  of  stimulation,  one 
of  the  halves  will  protrude  and  the  other  will  be  retracted. 

In  hemiplegia  patients  the  tongue  deviates  to  the  side  of  the  injured 
hemisphere.  This  deviation,  as  is  well  known,  is  not  entirely  due  to 
paralysis  of  the  retractor  muscle  of  one  side,  but  also  to  that  of  the 
protrusor  muscle  of  the  other  side. 

The  motor  cortical  area  of  the  tongue  contains  a  certain  number  of 
points  whose  isolated  stimulation  produces  these  different  movements. 
At  the  superior  part  of  this  area  the  movement  produced  is  that  of 
protrusion  with  lateral  deviation  ;  at  the  middle  part  a  movement  of 
torsion  of  the  tongue,  the  lingual  being  directed  to  the  cheek  of  the 
corresponding  side  ;  at  the  inferior  part,  a  movement  of  retraction. 
These  centres  are  arranged  in  graduated  stages  along  the  fissure  of 
Rolando,  from  its  knee  (in  the  monkey)  as  far  as  its  inferior  extremity. 

The  mouth  and  the  lips  also  present  various  movements  of  the  same 
kind,  often  associated  with  those  of  the  tongue. 

Mastication. — Stimulation  of  a  region  of  the  cortex  situated  at  the 
inferior  part  of  the  ascending  frontal  causes  regular  and  rhythinical 
movements  of  mastication  (alternate  lowering  and  raising  of  the  lower 
jaw  with  combined  movement  of  the  tongue),  lasting  as  long  as  the 
stimulation  continues,  and  ceasing  with  it. 

Swallowing. — Stimulation  of  a  neighbouring  area  (in  front  of  the 
preceding  one)  provokes,  one  might  almost  say,  attracts  a  movement 
of  swallowing.  It  is  known  that  this  act  is  voluntary,  in  the  sense  that 
we  can  bring  it  about  in  ourselves  Avith  the  mouth  empty,  but  once 
started  w^e  cannot  stop  it  in  any  one  of  its  phases.  Stimulation  of  the 
cortex  seems  to  correspond  to  this  initial  provocation,  acting  as  a  sort 
of  unlatching  of  the  automatic  mechanism,  and  this  as  nmch  for 
mastication  as  for  swallowing. 

Laryngeal  movements. — The  movements  of  the  larynx  also  corre- 
spond to  various  functions  and  thus  enter  into  numerous  associations. 
Certain  of  these  movements,  resulting  especially  in  the  adduction  and 
tension  of  the  vocal  cords,  are  vocal ;  they  are  respiratory  as  regards 
certain  others  which  ensure  their  abduction,  and  in  both  cases  are 
associated  in  their  turn  with  different  movements  of  the  thorax  which 
stimulation  of  determinate  points  of  the  cortex  also  elicits.  In  the 
dog  the  centre  of  these  respiratory  movements  is  in  the  inferior  third 
of  the  pre-crucial  gyrus,  and  that  of  the  vocal  movements  lies  below 
the  preceding  (Frangois-Franck,  Lepine,  Bochefontaine,  etc.).  Move- 
ments of  the  larynx  (its  elevation)  are  also  associated  with  those  of 
swallowing  when  the  area  of  these  movements  is  stimulated  (Semon 
and  Horsley). 


TACTILE  INNERVATION  537 

Remark. — That  which  characterizes  the  degi-ee  of  differentiation  of  a  move- 
ment, from  the  point  of  view  of  its  cortical  representation,  is  not,  as  will  be 
obvious,  its  complexity  (there  are  very  complicated  movements  which  are  aiito- 
matic  ;  there  are  very  simple  ones  which  are  voluntary)  ;  it  is  rather  its  co^i- 
tingency,  that  is  to  say,  its  realization  independently  of  that  of  other  movements, 
with  which,  however,  it  may  sometimes  be  associated,  according  to  circiun- 
stances.  The  movements  of  the  thumb,  compared  to  those  of  the  fingers  and 
the  toes  of  the  foot,  are  a  striking  example  of  this  :  they  liave  a  cortical  repre- 
sentation which  is  obviously  advantageous  compared  witli  otlier  movements. 

Bulbar  and  pseudo-bulbar  paralyses. — When  the  motor  paralysis  is  complete, 
and  affects  the  two  sides  of  the  body  equally,  it  is  possible  that  the  lesion  which 
has  produced  it  is  seated  in  the  medulla  oblongata  or  the  spinal  cord,  localities 
in  which  the  motor  paths  of  the  two  sides  of  the  body  are  approximated  and 
condensed,  so  as  to  render  them  liable  to  be  involved  by  a  single  destructive 
lesion  (labio-glosso-laryngeal  paralysis)  ;  while  the  brain,  owing  to  its  size  and 
to  its  division  into  two  liemispheres,  is  usually  the  seat  of  lesion  on  one  side 
■only.  But  it  may  happen  tliat  very  localized  cerebral  lesions,  which  are  at  the 
same  time  both  double  and  symmetrical,  occasionally  jn-oduce  jjaralyses  affect- 
ing both  sides  of  the  body  :  these  are  the  pseudo-bulbar  paralyses.  They  may 
result  from  various  combinations  of  cerehral  lesions,  affecting  in  the  two  hemi- 
spheres conducting  fibres  of  similar  function,  but  which  are  injxired  at  variable 
points  of  their  course,  either  on  one  or  the  other  side  (cortex,  corona  radiata, 
corjous  striatum,  corpus  callosum,  etc.)  (Brissaud).  It  must  be  understood  that 
somewhat  marked  differences  separate  bulbar  i^aralysis  proper  and  that  known 
as  pseudo-bvilbar,  botli  as  regards  theii"  clinical  course  and  also  as  concerns 
symiitomatology.  The  most  essential  distinction  between  them  is  that  the 
first  abolishes  the  reflex  movements  necessary  for  the  performance  of  the  j^ri- 
mordial  functions,  from  which  arises  its  special  gravity  ;  and  the  second  abolishes 
the  voluntary  movements. 

Epileptiform  attacks. — After  the  stimulation  has  been  several  times  renewed, 
the  cortex,  like  all  cyclic  systems',  especially  when  of  a  comjDlex  natiu-e,  retains 
something  of  the  stimulus  after  each  renewal  ;  and  its  highly  augmented  irri- 
tability is  soon  manifested.  The  stimulation  may  then  cause  the  appearance 
•of  veritable  epileptic  crises,  resembling  attacks  of  haut  mal. 

All  animals  are  not  equally  liable  to  manifest  this  phenomenon.  The  dog, 
the  cat  (Frangois-Franck),  and  the  monkey  (Ferrier)  are  the  most  suitable. 
The  rabbit,  the  horse,  the  ass,  the  sheep,  the  goat  do  not  display  an  epileptic 
reaction  (Albertoni)  ;  the  guinea  pig,  which  yields  it  so  easily  under  the  influ- 
■ence  of  jjeripheral  stimulations,  is  not  liable  to  any  crisis  as  the  result  of  the 
•direct  stimulation  of  tlie  brain. 

The  most  efficacious  excitant  is  the  alternating  induced  electric  ciu-rent. 
Mechanical  stimulation  is  but  little  adapted  for  provoking  the  activity  of  the 
brain.  It  is  nevertheless  efficacious  in  certain  conditions  (Luciani),  which  are 
indeed  those  facilitating  the  development  of  the  epileptiform  attacks. 

The  most  favourable  condition  is  that  of  an  inflammatory  state  of  the  cerebral 
surface  under  stimulation. 

Characters. — The  epileptiform  attack  is  distinguished  from  the  ordinary 
tetanic  attack  by  the  following  characteristics  :  (1)  it  svirvives  the  stimvilation 
after  the  latter  has  ceased  ;  sometimes,  indeed,  it  increases  in  intensity-  after 
the  cessation  of  the  stimulus,  as  if  the  latter  had  brought  certain  arresting 
influences  into  play  which  at  first  moderated  its  motor  effect  ;  (2)  it  has  a 
tendency  to  be  propagated  to  the  muscular  gi'oups  near  to  those  directly  de- 
pendent on  the  stimulated  area,  and  even  to  sjDread  to  the  whole  of  the  muscular 
system  of  the  animal.     This  propagation  ensues  gradually  according  to  certain 


538 


SPECIAL  INNERVATIONS 


laws  which,  however,  are  not  always  respected,  and  from  above  downwards  or 
below  upwards,  according  to  the  point  of  departure.  It  no  doubt  acts  through 
the  cortical  and  cerebral  paths  themselves,  rather  than  through  some  convulsive 


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Fig.   22(i. — Motor   capsular   localizations   in   the   Macacus   sinicus   (after   Beevor   and) 
Horsley,  Philos.  Trans.,  1890). 

Successive  sections  of  the  internal  capsule  from  above  downwards. 


centre,  as  has  been  sometimes  supposed.  We  may  add  that  the  epileptic  attack 
arises  exclusively  from  the  stimulation  of  the  cortex,  and  in  no  sense  fron:i  that 
of  the  white  matter  whenever  the  first  has  been  carefully  removed  (Fran^ois- 
Franck). 

Tliis  character  may  be  likened  to  that  rendered  evident  by  clinical  observa- 


TACTILE  INNERVATION 


539 


tion  in  idiopathic  epilepsj-,  in  which  the  attack  is  usually  preceded  by  an 
aura  seated  in  some  locality  of  the  body,  which  serves  as  a  point  of  departure 
for  the  con\-ulsions.  In  man  partial  epilepsies.  liemipJegic  epilepsies  and 
generalized  epilepsies  may  be  observed. 


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Fig.  226  {continued). — Motor  capsular  localizations  in  the  Macactis  sinicus  (after  Beevor 
and  Horlsey,  Philos.  Trans.,  1890). 

Successive  sections  of  the  internal  capsule  from  above  downwards. 


The  comatose  condition  which  follows  the  attack  in  man  may  also  be  observed 
in  animals.  And  also,  as  in  man,  the  attack  may,  after  a  time,  be  renewed 
without  direct,  or  at  least  apparent,  provocation. 


540  SPECIAL  INNERVATIONS 

Wlien  animals  are  kept  alive  after  certain  superficial  injvu'ies  of  the  cortex, 
attacks  of  this  nature,  arising  quite  spontaneously,  may  sometimes  be  observed 
(Hitzig). 

Progress  and  phases  of  the  attack. — The  attack  thus  provoked  displays  the 
two  classic  phases  :  the  one  of  tonic  contraction  maintained  with  slight  rein- 
forcements ;  the  other  of  clonic  contraction  presents  dissociated  convulsions, 
which  decrease  and  occur  at  longer  intervals.  Sometimes  the  first  of  these 
phases  is  wanting,  and  varieties  may  be  noticed  as  regards  the  course  of  the 
attack.  A  return  to  repose  is  the  rule  ;  but  according  to  the  intensity  of  the 
sti^iiulation,  its  more  or  less  frequent  repetition,  the  susceptibility  of  the  animal, 
and  the  state  of  the  cortex  itself,  the  number  of  consecutive  attacks  may  be 
increased  ;  they  may  become  subintrant,  and  death  may  supervene  diiring  the 
fit.  Stimulation  of  the  cortex  in  animals  which  are  kept  alive  seems  to  create 
in  them  an  epileptic  tendency. 

When  once  the  attack  has  commenced,  if  the  hemispheres  be  separated  from 
the  sub-cortical  centres  of  the  cord  the  effects  are  the  same.  Hence  it  results 
that  the  cortex  creates  and  propagates  the  initial  stimulation  into  its  substance, 
but  that  the  associations  which  bring  it  about  are  external  to  it.  This  fact 
resembles  many  others  of  the  same  kind  tending  to  the  same  conclusion. 

Internal  epilepsy. — The  epileptiform  reaction  thus  initiated  reverberates  on 
the  functions  of  organic  life  :  there  is  an  internal  eqnle'psy  which  may  be  dis- 
sociated from  the  other  type  of  the  malady,  by  suppressing  the  motor  effects 
of  the  life  of  relation  with  curare.  Thus  dissociated,  the  internal  manifestation 
is  a  characteristic  one  (Fran9ois-Franck). 

Respiration. — Cerebral  stimulation  usually  has  different  effects  on  respiration, 
and  manifests,  according  to  circumstances,  two  tendencies  :  one  to  inspiration, 
the  other  to  expiration,  but  with  concordance  of  the  glottic  or  other  phenomena 
which  assvire  the  performance  either  of  the  first  or  the  second  of  these 
actions.  Stimulation  followed  by  an  epileptic  attack  has,  on  the  contrary,  dis- 
cordant effects,  which  are  rendered  evident  by  the  closing  of  the  glottis,  the 
energetic  contraction  of  the  muscles  of  the  thorax  and  of  the  diaphragm,  the 
augmentation  of  the  intrathoracic  pressure,  and  the  imminence  of  asphyxia 
(mechanism  of  prolonged  effort).  This  arrest  of  breathing  is  interrupted  by 
respirations  during  the  clonic  phase.  The  two  jDhases  are  not  necessarily  or 
regularly  concordant  with  similar  phases  as  regards  the  muscles  of  the  skeleton. 
In  jDartial  attacks  an  expiratory  condition,  without  complete  closing  of  the 
glottis,  is  most  usually  observed. 

Circulation. — During  a  severe  attack  the  tonic  phase  is  manifested  by  a 
slowing  of  the  heart's  action,  and  the  clonic  phase  by  an  acceleration  of  its 
movements  ;  the  reaction  being  prolonged,  however,  in  a  noteworthy  manner 
after  the  end  of  the  stimulation.  During  the  whole  of  the  attack,  the  vessels 
undergo  an  energetic  contraction.  This  state  of  the  vessels,  combined  with 
the  preceding  changes  and  with  opposite  phases  of  the  activity  of  the  heart, 
often  causes  the  pressure  to  be  augmented,  but  it  may  undergo  converse  varia- 
tions, in  spite  of  the  generally  contracted  state  of  the  circulatory  system. 

Pupil  of  the  eye. — The  artificially  excited  epileptic  attack  in  animals  is  attended 
by  two  symptoms  which  are  very  characteristic  of  the  attack  as  observed  in 
man  :  the  first  of  these  is  the  alteration  in  the  diameter  of  the  pupil  which,  in 
epilepsy,  is  invariably  in  the  direction  of  dilatation. 

Salivary  secretion. — The  second  symptom  is  the  secretion  of  saliva,  which 
occurs  at  the  beginning  of  the  clonic  phase  of  the  attack  (Fran5ois-Franck). 

Bladder. — There  is  at  the  same  time  contraction  of  the  muscles  of  the  bladder, 
and  sometimes  expulsion  of  urine. 

The  epilepsy    known    as  Jacksonian. — Limited    foci  of  haemorrhage  and    of 


TACTILE  INNERVATION  541 

softening  of  the  brain  often  induce  reactions  of  an  inflanimatorj-  nature  in  the 
cerebral  cortex,  which,  by  local  stimulation  of  the  cortex,  give  rise  to  partial 
attacks  of  epile})sy  (Huglings  Jackson).  These  attacks,  according  to  the  nature 
of  their  situation,  may  be  rendered  evident  by  convulsions  of  the  face,  con- 
jugated deviation  of  the  eyes,  etc.  The  deviations  thus  produced  in  the  posi- 
tion of  the  limbs  or  of  the  areas  affected  are  naturally  the  oj^posite  of  those 
which  resulted  in  the  first  instance  from  theu-  paralysis.  Thus  a  lesion  of  the 
left  hemisphere  which  involves  by  paralysis  a  deviation  of  the  eyes  to  the  left 
would,  if  this  lesion  induces  epilepsy,  bring  about  a  deviation  of  the  eyes  in 
the  oj^posite  direction,  that  is  to  say,  to  the  right  ;  according  to  the  mnemo- 
teclmical  formula  adopted  in  the  one  case,  the  patient  looks  at  his  lesion  ;  in 
the  other,  at  his  convulsed  limbs. 

These  joartial  attacks  may  also  be  generalized  to  a  certain  extent  :  in  this 
case  the  invasion  proceeds  from  the  cortical  area  which  controls  the  muscles 
convulsed  to  the  neighbouring  areas  which  are  progressively  affected. 

Epilepsy  caused  by  absinthe. — Essence  of  absinthe,  when  injected  in  the  blood 
of  animals,  gives  rise  to  epileptic  attacks  in  them  (Magnan).  The  convulsions 
are  then  of  medullary  origin,  as  in  this  case  the  poison  suppresses  the  cerebral 
activity  and  excitability,  while  exaggerating  that  of  the  medullary  centres 
(Frangois-Franck). 

D.  MUSCULAR  SENSE.— CIN^STHESIC  IMPRESSIONS 
The  organs  receptive  of  the  stimulus  in  general  sensibility  are  not 
altogether  confined  to  the  skin,  and  the  sensation  of  contact  of  external 
objects,  with  their  qualities  of  form  or  of  temperature,  is  not  the  only 
one  which  characterizes  the  tactile  sense.  The  muscles  receive  imjmlses 
from  the  nervous  system  which  j^rovoke  them  to  movement  ;  in  their  turn, 
by  their  oum  movements,  they  comyniinicate  impulses  to  the  nervous  system. 
Thus  is  made  evident  the  reciprocal  influence  of  sensation  on  move- 
ment, and  of  movement  on  sensation. 

We  thus  see  that  the  tactile  system  receives  impulses,  some  external, 
by  the  cutaneous  surface,  others  internal,  by  the  muscular  apparatus. 
Not  only  the  muscles,  but  also  their  immediate  prolongations,  the 
tendons  and  the  other  passive  parts  of  the  motor  apparatus,  furnish 
impulses,  amongst  which  distinctions  have  still  to  be  made.  The 
hones  possess  a  sensibility  of  an  obscure  nature  ;  the  ligaments,  the 
membranes  of  the  joints,  and  all  those  parts  which  are  more  immediately 
submitted  to  the  movement  of  the  levers  of  the  skeleton,  are  sensor}^ 
in  the  same  way  as  the  tendons. 

Anatomical  data. — The  muscles,  the  tendons,  the  aponeuroses,  that  is  to  say, 
the  organs  which  make  or  transmit  movement,  possess  sensory  nerves.  In  the 
inuscles,  these  nerves  are  very  distinct  from  those  which  come  into  contact  with 
the  contractile  substance  of  the  primitive  bundles  at  the  level  of  the  terminal 
motor  i^lates.  Their  different  characters  are  as  follows  :  each  muscle  receives 
a  small  number  of  branches  of  this  nature,  of  which  each  is  divided  into  a  very 
large  number  of  ramifications.  These  ramifications,  after  having  lost  their 
sheath  of  Henle,  their  myelin  sheath,  are  finally  reduced  to  bare  axis  cylinders, 
which  terminate  by  free  extremities.     These  extremities  remain  in  the  inter- 


542  SPECIAL  INNERVATIONS 

stitial  tissvie,  rarely  in  direct  contact  with  the  mnscnlar  fibres,  never  in  the 
interior  of  these  fibres. 

The  tendons  for  their  part  possess  similar  terminations,  which,  after  being 
reduced  to  bare  axis  cylinders,  are  placed  between  the  tendinous  bundles  and 
terminate  by  free  extremities,  either  enlarged,  flattened  or  varicose.     In  birds, 


Fig.   227. — Corpuscle  of  Golgi  of  the  tendo  Achillis  in  man  (deprived  of  its  lamellary 

sheath). 

FM,  muscular  fibres  ;    FT,  tendon  fibres  ;    CA,  nerve  fibre  (axis  cylinder  bare)  ;  RT,  RT,  its 
terminal  ramifications  on  the  surface  of  the  tendon  bundles  (after  M.  Duval). 

mammals,  and  especially  in  man,  at  the  union  of  the  tendon  with  the  muscle, 
other  organs,  distinct  from  the  preceding,  are  found  ;  these  are  the  corpuscles 
known  as  those  of  Qolgi.  They  are  formed  of  two  or  three  little  tendinous 
bvmdles  continuous  with  the  muscular  bundles  ;  they  are  spindle-shaped,  and 
are  covered  with  a  laminated  sheath  lined  with  endothelium.  They  are  accom- 
panied by  from  two  to  four  nervous  fibres,  which,  ramified  in  the  form  of  un- 
covered fibrilli3e,  are  arranged  on  the  surface  of  the  fusiform  bundle  (below  the 
sheath  of  the  corpuscle),  and,  from  this  fact,  present  a  vague  resemblance  to 
the  inotor  terminal  plates.  They  are,  in  fact,  sensory  organs  ;  this  has  been 
demonstrated  by  Cattaneo  by  means  of  the  method  of  degenerations.  They 
degenerate  after  section  of  the  posterior  roots,  as  do  sensory  nerves  ;  the  motor 
terminations,  on  the  contrary,  degenerate  after  the  section  of  the  anterior  roots. 

Erroneous  terminology.— The  expression  "  muscular  sense  "  has 
been  made  use  of  to  designate  all  the  deep  sensibilities  which  supply 
us  with  information  concerning  the  execution  of  movements.  The 
term  is,  however,  incorrect  for  the  two  following  reasons  :  (1)  the 
impressions  which  are  furnished  by  the  muscles  only  constitute  a  part 
of  the  deep  post-motor  impulses  controlling  the  movement  ;  a  large 
number  come  from  the  articulations,  the  ligaments,  and  even  from  the 
bones  :  (2)  these  impressions  are  most  frequently  unconscious,  and 
are  on  this  account  distinguished  from  those  of  the  senses,  properly 
so  called,  like  sight  or  touch. 

Synonyms. — The  muscular  sense  of  Ch.  Bell  has  been  called  by 
E.  H.  Weber,  the  sense  of  force,  by  Gerdy  and  by  Landry  the  perceptioii 
of  muscular  activity,  by  Duchenne  muscular  consciousness,  by  Bain 
sense  of  movement,  by  Wundt  sense  of  innervation,  by  Hamilton,  loco- 
motive  faculty,  by  Bastian  kincesthesic  impressions,  and  by  Bonnier 
sense  of  attitude.  If  amongst  these  designations  there  are  some  which 
are  equivalent  or  synonymous,  there  are  others  implying  a  different 
conception  of  the  phenomenon  which  they  profess  to  explain. 


TACTILE  INNERVATION  543 

Starting  point  and  localization  of  the  muscular  sense. — For  the  larger  number 
of  observers  the  starting  point  of  the  impressions,  which  are  at  the  foundation 
of  the  sense  of  movement  or  sense  of  force,  is  peripheral,  and  located  either  in 
the  muscles  exclusively  (Ch.  Bell,  Gerdy,  Landry,  Duchenne),  or  in  the  totality 
of  the  organs  participating  in  movement  (Bastian).  For  Bain  and  for  Wundt, 
these  impressions  are,  on  the  contrary,  confined  to  the  nervous  system  itself  ; 
they  would  in  the  latter  be  contemjooraneous,  not  indeed  with  visible  move- 
ment when  about  to  be  realized  in  the  muscles,  but  with  the  centrifugal  nervous 
wave  which  leaves  the  brain  to  reach  these  organs  ;  they  would  consequently 
be  anterior  to  muscular  movement,  thus  giving  it  direction  and  expression  before 
its  performance.  The  nerves  we  call  motor  would  be  conscious  of  the  move- 
ments to  which  they  give  rise  ;  and  this  ivithout  the  participation  of  the  sensory 
nerves  ;    this,  and  nothing  else,  is  what  sense  of  movement  really  means. 

This  conception  appears  to  us  to  be  quite  out  of  harmony  with  the  principles 
we  have  deduced  from  the  examination  of  the  fundamental  facts  of  the  phj-si- 
ology  of  the  nervous  system.  These  facts  prove  most  assuredly  that  the  nerves, 
both  those  called  sensory  and  those  known  as  motor,  are  in  a  strict  and  reci- 
procal dependence,  to  such  a  degree  that  it  is  sometimes  difficult  to  distinguish 
sensation  from  motion  and  motion  from  sensation  ;  but  we  are  not  authorized 
on  this  account  to  maintain  that  the  one  can  rejalace  the  other  to  the  extent 
of  performing  the  functions  of  either.  The  nervous  wave  which  ascends  towards 
the  brain  is  essentially  connected  with  the  development  of  sensibility  ;  that 
descending  from  it  is,  for  its  part,  connected  with  the  execution  of  movement. 
No  true  nervous  act  is  comjolete  in  itself  except  by  the  association  of  the  two 
orders  of  nerves  ;  to  maintain  that  the  descending  wave  can  by  itself  give  rise 
to  a  sensori-motor  act,  even  one  of  the  simplest,  is  a  physiological  absurdity. 

Control  of  the  movements  by  the  different  senses  and  the  various  gradations 
of  the  same  sense. — Patients  who  have  lost  cutaneous,  but  have  retained 
muscvilar,  sensation,  do  not  suffer  any  great  distiu'bance  as  regards  their  move- 
ments ;  but  when  there  is,  at  the  same  time,  loss  of  muscular  and  osseous  sensa- 
tion the  execution  of  movements  becomes  very  difficult.  They  may  still  be 
performed,  however,  under  the  control  of  the  sense  of  sight,  but  in  the  dark  (or 
if  the  eyes  are  shut)  they  are  very  much  embarrassed  ;  they  are  no  longer 
adjusted  and  proportioned  to  the  end  to  be  attained  ;  they  may  even  become 
altogether  impossible.  The  patient  is  unable  to  realize  that  he  does  not  per- 
form them,  when  he  has  the  will  to  do  so  ;  or  if,  when  executing  them  with  the 
help  of  the  sense  of  sight,  he  shuts  his  eyes,  he  is  incapable  of  arresting  them 
(Duchenne). 

Psychic  images  of  movement. — The  question  is,  however,  a  very 
complex  one,  and  analysis,  in  proportion  as  it  becomes  more  searching, 
regards  it  from  more  numerous  points  of  view.  The  performance  of 
muscular  movement  produces  cinaesthesic  impressions  which,  through 
their  appropriate  sensory  tracts,  ascend  to  the  brain  and  are  synthe- 
tized  into  psychic  images  representative  of  these  movements.  They 
are  called  motor  images  because  they  become,  in  their  turn,  a  source  of 
descending  impulses,  again  realizing  the  movement  in  its  antecedent 
form.  It  would  be  better  to  call  them  sensor i-7notor  because,  though 
they  result  in  movement,  yet  they  have  taken  their  origin  in  sensation. 

In  all  these  examples  the  movement  is  a  real  one,  and  we  observe  it  to  be, 
by  tm-ns,  both  the  effect  and  the  cause  of  impressions,  of  more  or  less  conscious 


544  SPECIAL  INNERVATIONS 

sensations  ;  but  there  are  eases  where  the  representation  of  a  movement  is 
present  in  ovir  consciousness,  witliout  tlie  muscles  bringing  it  into  being.  The 
image  of  the  movement  is  within  ourselves  and  is  a  conscious  one,  while  our 
muscles  remain  in  a  state  of  repose.  It  may  be  supposed  in  this  case,  as  in  the 
jjreceding,  that  the  nervous  action  is  spread  out  in  a  sensori-motor  cycle,  formed 
of  elements,  some  of  which  are  ascending  and  others  descending,  but  which  in 
neither  case  reach  the  muscles.  This  cycle  is  constructed  in  the  same  way  as 
the  one  connecting  the  spinal  cord  to  the  muscles  by  sensory  and  motor  nerves, 
but  is  situated  above  it  :  with  the  exception  that  the  organs  of  visible  move- 
ment are  lacking,  its  action  is  the  same  ;  the  ascending  impulses  are  reflected 
here  as  descending  impulses,  and  these  latter,  in  their  turn,  cause  ascending 
impulses  to  be  reproduced  which  give  rise  in  the  consciousness  to  the  repre- 
sentation of  a  movement  having  no  real  existence.  This  representation  cannot 
be  described  as  an  illusion,  as  we  are  perfectly  conscious  of  the  non-performance 
of  the  movement. 


Various  elements. — Thus  in  the  impressions  which  have  been  called 
cinsesthesic,  diverse  elements  take  part  ;  besides  cutaneous  sensibility, 
there  are  at  least  three  more  if  we  distinguish  them  by  the  organs  which 
are  the  starting  point  of  these  various  impressions  :  namely,  the 
muscular  sensibility ,  the  articular  sensibility,  and  the  osseous  sensibility. 

A.  Muscular  sensibility. — This  is  the  variety  concerning  which 
the  largest  number  of  experimental  observations  has  so  far  been  made. 

1.  Its  proofs. — The  muscles  are  obviously  sensitive  to  ordinary  stimuli. 
such  as  pinching,  pressure,  electrization.  Their  sensibility  is  particu- 
larly obvious  in  patients  who  have  lost  cutaneous  sensibility  in  the 
regions  where  the  skin  covers  the  muscles.  These  subjects  distinguish 
distinctly  these  different  stimuli  when  applied  to  the  muscles  through 
the  anaesthetic  skin  :  further,  they  are  conscious  of  both  the  active 
and  passive  movements  of  these  same  muscles,  and  also  of  any  resist- 
ance opposed  to  their  contraction  (Duchenne).  In  animals,  if  a  branch 
of  a  nerve  which  is  entirely  exhausted  in  a  muscle  is  laid  bare  and 
then  pinched,  not  only  is  the  muscle  seen  to  contract,  but  evidences 
of  conscious  or  reflex  sensibility  are  also  observed.  As  a  rule,  the  fibres 
of  the  niuscular  sense  are  mixed  with  the  motor  fibres  throughout  the 
length  of  the  mixed  nerve  trunk  (except  as  regards  the  roots)  ;  but 
exceptionally  muscles  may  be  found  to  which  the  motor  and  sensory 
fibres  are  supplied  by  isolated  trunks  (Chauveau). 

2.  Irritability  and  muscular  consciousness. — The  connexion  effected 
between  the  motor  and  the  sensory  nerves  in  the  muscle,  a  link  which 
is  demonstrated  both  by  anatomy  and  physiology,  has  a  very  important 
signification.  It  may  be  compared  with  that  contracted  by  the  sensory 
nerves  with  the  motor  nerves  in  the  grey  matter  of  the  nervous  system, 
and  it  completes  the  close  concatenation  which  links  together  sensation 
and  motion  in  a  twofold  manner.     The  wholly  internal  bonds  uniting 


TACTILE  INNERVATION  545 

these  two  phenomena  in  what  we  call  cellular  irritability  (of  which 
muscular  contractility  is  an  example),  appear  to  us  to  be,  in  a  sense, 
exteriorized  and  rendered  visible  by  the  organization  of  the  nervous 
system. 

3.  Sensory  nerves  of  the  muscles. — These  deep  anaesthesias  are  met 
with,  in  the  human  species,  in  morbid  conditions,  and  principally  in 
hysterical  patients.  They  may  be  induced  in  animals,  more  especially 
in  two  muscles  :  the  sterno-mastoid  and  the  oesophagus,  in  the  horse. 
These  muscles  receive  their  sensory  and  motor  nerves  by  distinct  paths, 
which  makes  it  possible  to  act  separately  on  either  and  to  observe 
what  change  will  affect  the  movement  when  the  sensory  nerve  is  cut, 
and  when  it  is  stimulated. 

Sterno-mastoid  muscle. — The  motor  nerve  of  the  sterno-mastoid 
comes  to  it  from  a  ramification  of  the  external  branch  of  the  spinal 
accessory  ;  its  sensory  nerve  is  furnished  by  the  inferior  branch  of 
the  second  cervical  pair.  Section  of  this  latter  nerve  (sensory  nerve), 
when  effected  on  one  side,  does  not  alter  in  any  perceptible  manner 
the  nature  of  the  movement  of  the  sterno-mastoid  muscle  when  its 
contraction  on  one  side  is  compared  with  that  on  the  other.  The 
movement  in  question  is  also  a  very  simple  one  ;  it  aids  in  producing 
flexion  of  the  head  (Chauveau). 

(Esophageal  muscle. — The  oesophagus  receives  its  motor  ramifications 
from  the  pharyngeal  and  the  external  laryngeal  nerves  ;  its  sensory 
nerves  come  to  it  by  a  recurrent  course  from  the  inferior  portion  of  the 
vagus,  especially  from  the  inferior  laryngeal  nerve  ;  they  may  be 
affected,  to  the  exclusion  of  the  preceding,  by  cutting  the  vagi  or  the 
recurrent  nerves.  It  is  true  that  these  sensory  nerves  are  distributed 
both  to  the  mucous  membrane  and  to  the  oesophageal  muscle  through 
fibres  which  are  mixed  in  the  recurrent  nerves.  But  it  is  also  known 
that  the  sensibilitj^  of  the  oesophageal  mucous  membrane  takes  only 
an  insignificant  part  ii^i  the  performance  of  the  movement  of  swallow- 
ing, while  this  movement  is  continued  in  the  oesophagus  with  its 
normal  characteristics  in  the  act  of  deglutition  when  nothing  is 
swallowed  ;  and,  further,  stimulation  of  the  sensory  mucous  filaments 
does  not  induce  the  refiex  movement  of  swallowing.  We  may  then  put 
the  sensibility  of  the  mucous  membrane  out  of  court.  But  section  of 
the  vagi  or  of  the  inferior  laryngeal  nerves  (sensory  nerves)  disturbs  the 
peristaltic  movement  of  deglutition  to  such  a  degree  as  to  be  equiva- 
lent to  the  section  of  the  pharyngeal  branches  (motor  nerves)  ;  the 
oesophagus  often  seems  to  be  paralysed  ;  it  becomes  encumbered 
with  food  (especially  in  the  inferior  part  of  its  cervical  region)  ;  some- 
times it  suffers  from  a  kind  of  ataxy  which  causes  it  to  contract  almost 

p.  N  N 


546  SPECIAL    INNERVATIONS 

simultaneously  and  irregularly  in  the  whole  of  its  length.  Stimulation 
of  the  central  end  of  these  centripetal  oesophageal  nerves  gives  rise  to 
a  simultaneous  tetanus  of  the  whole  of  the  oesophageal  muscle,  similar 
to  that  resulting  from  direct  stimulation  of  its  motor  nerves,  the  only 
difference  being  that  it  appears  after  a  somewhat  prolonged  delay. 
All  these  experiments  show  that  the  nerves  of  the  muscular  sense  are 
essential  to  the  normal  performance  of  the  movements  of  the  oeso- 
phagus (Chauveau). 

4.  Independence  of  muscular  contractility  and  of  the  muscular  sensi- 
Ijility^ — It  will  thus  be  seen  that  a  muscle  may  be  paralysed  as  regards 
naovements  and  yet  may  retain  its  sensibility,  or  reciprocally,  according 
to  whether  certain  alterations  affect  its  motor  or  its  sensory  nerves. 
Eor  example,  in  hysterical  subjects,  sensibility  will  be  found  to  have 
disappeared  in  certain  muscles,  and  these  may  at  the  same  time  be 
the  seat  of  contractions  which  the  patient  does  not  feel. 

5.  Different  modalities  of  the  muscular  sensibility. — Resembling  all 
others,  the  muscular  sensibility  displays  different  modalities,  arising 
in  common,  but  each  having  a  specific  aspect.  What  contributes  to 
give  them  interest  is  that  disease  is  capable,  in  certain  cases,  of  dis- 
sociating them.  We  may  distinguish  :  (1)  sensibility  to  external 
stimuli  and  to  compression  which,  in  healthy  subjects,  produces  a  par- 
ticular sensation,  different  from  that  given  by  pressure  of  the  skin,  or 
of  another  organ  ;  it  may  disappear  in  syphilitic  and  hysterical 
patients,  and  may  sometimes  be  exaggerated  in  those  suffering  from 
lead  poisoning  ;  (2)  the  sensatioji  of  contractioyi  of  the  muscle,  vfhich. 
is  often  destroyed  in  hysterical  patients  ;  (3)  muscular  fatigue,  which 
is  only  an  exaggeration  of  the  preceding  and  which,  like  it,  may  dis- 
appear. 

B.  Osseous  sensibility. — The  bones,  like  the  muscles,  are  sensitive 
organs.  Their  deep  situation  prevents  their  sensibility  being  examined 
except  through  the  skin,  which  is  itself  more  sensitive  than  they  are. 
It  has  sometimes  been  possible  to  test  osseous  sensibility  in  cases  of 
cutaneous  anaesthesia.  Max  Egger  has  shown  that  the  vibrations  of 
a  tuning  fork,  placed  on  a  limb  or  some  region  of  the  body,  affect  osseous 
sensibility  in  a  manner  almost  specific,  and  not  that  of  the  skin.  In 
fact,  in  the  case  of  cutaneous  anaesthesia  these  vibrations  cannot  affect 
the  skin.  And  it  is  then  the  corresponding  bones  which  are  sensitive 
to  these  vibrations,  if  the  anaesthesia  is  not  deep.  In  the  case  of  deep 
anaesthesia,  they  are  not  perceived  when  the  cutaneous  sensibility  is 
intact.  The  physiologist  and  the  clinician  have  thus  a  means  of  in- 
terrogating the  osseous  sensibility,  even  through  the  cutaneous  integu- 
ments when  these  latter  retain  their  special  sensibility  ;   a  tuning  fork 


TACTILE  INNER VATIOX  547 

yielding  128  vibrations  to  the  second  would  be  the  most  suitable  for 
this  kind  of  experiment. 

C.  Articular  sensibility. — The  articulations  formed  by  the  heads 
of  the  long  bones  and  the  membranes,  capsules,  or  ligaments  uniting 
them,  are  sensitive,  inasmuch  as  these  different  structures  are  provided, 
like  the  tendons,  with  organs  receptive  of  impulses  and  centripetal 
nerves.  The  tension  of  the  ligaments  and  the  rubbing  of  the  surfaces 
in  contact  produce  these  stimuli. 

Experimental  dissociation  of  the  cutaneous  and  deep  sensibilities. — The  lower 
liml)  of  the  bird  has  been  made  use  of  to  bring  about  this  dissociation  experi- 
mentally. The  absence  of  muscles  in  the  foot  of  the  bird  allows,  by  cutting  the 
nerves  which  enter  into  this  extremity,  of  the  complete  abolition  of  sensation 
in  the  toes  without  compromising  the  motricity  of  any  of  the  muscles  of  the 
leg.  The  section  suppresses,  it  is  true,  sensation  in  the  articulations  of  the 
foot,  but  leaves  intact  that  of  the  muscles.  The  bipedal  position  of  birds  in 
standing  still  and  w^alking  renders  this  experiiuent  a  very  striking  one. 

Chau\'eau,  in  tame  pigeons,  having  cut  the  four  nerves  of  the  leg  arotmd  the 
articulation  of  the  tarsus,  studied  the  result  of  this  insensibility. 

(a)  In  repose. — Dvu-ing  sleep,  the  subjects  perched  quite  indifferently  either 
on  the  enervated  or  the  intact  foot,  and  also  on  both  together. 

(b)  In  ivalkin'j. — "  When  the  subject  was  jjlaced  on  the  gi'ound  after  the 
operation,  it  seemed  to  exj^erience  soiue  hesitation  in  using  the  enervated  foot 
as  a  support  while  walking.  But  this  hesitation  did  not  last  long.  It  was 
shown,  at  the  moment  of  starting,  by  the  repetition  of  the  movement  of  placing 
the  claws  of  this  enervated  foot  in  contact  with  the  ground.  The  animal 
appeared  surprised  not  to  feel  the  contact  with  the  latter.  But,  once  it  had 
begun  to  walk,  the  pigeon  used  this  foot  as  freely  as  the  other." 

The  precision  of  the  movements  and  of  the  attitude  in  these  experiments 
shows  how  little  cutaneous  sensibility  is  necessary  to  the  co-ordination  of  efforts 
in  order  to  ensvu'e  their  normal  performance.  INIuscular  sensibility,  obviously 
retained,  must  play  here  a  part  of  the  utmost  imjiortance. 

1.  Conceptions  furnished  by  the  different  sensibilities. — The  ideas 
and  the  information  furnished  us  by  the  different  sensibilities,  both 
deep  and  superficial,  are  numerous.  Through  them  we  ascertain  if 
our  limbs  and  our  body  are  in  a  state  of  immobility  or  of  inovement  ; 
to  them  we  owe  the  power  of  distinguishing  in  ourselves  a  static  from 
a  dynamic  condition,  and  they  are  further  capable  of  defining  precisely 
each  of  these  two  states. 

Notion  of  the  position  of  the  limbs. — In  fact,  by  measuring  these 
impressions,  we  obtain  an  idea  of  the  positions  of  our  body  and  in- 
dividually of  our  limbs  in  the  varied  position  which  these  are  capable 
of  assuming  and  preserving.  This  conception  is  abolished  if  both 
cutaneous  and  deep  sensibility  become  paralysed.  This  loss  of  the 
idea  of  position  is  often  observed  in  pathological  conditions  of  the 
nervous  system. 

The  idea  of  the  position  of  the  limbs  probably  comes  to  us  from  impressions 


548  SPECIAL    INNERVATIONS 

gathered  together  in  a  permanent  manner,  either  by  tlie  skin  in  contact  with 
external  objects  (ground,  clothes,  sheets,  etc.),  or  by  contact  of  the  limbs 
between  themselves  (folding,  or  tension  of  the  skin,  etc.),  either  by  the  osseovis 
levers  and  esjaecially  the  articulations  ;  or  by  impressions  equally  permanent 
resulting  from  the  mutual  tensions  or  pressures  of  the  surfaces,  and  which 
vary  according  to  the  relative  position  of  tliese  articulated  levers.  We  have 
already  remarked,  with  regard  to  the  functions  of  tlie  sensory  roots,  that  a 
permanent  flow  of  impulses  reascends  througliout  tlie  length  of  these  con- 
ductors,  and    that   this  flow  is  of  very  varied   origin. 

2.  Cortical  localization  of  the  muscular  sense  and  the  cinaesthesic 
impressions. — The  muscular  sense  and  all  the  sensibilities  which  we 
call  deep  are,  individually,  most  usually  subconscious  or  even  uncon- 
scious ;  but  they  nevertheless  furnish  us.  by  their  associations,  Avith 
conscious  conceptions  concerning  the  state  of  our  bodies,  however 
little  the  attention  is  directed  to  it  and  its  different  mobile  segments. 
The  impressions  proceeding  from  the  deep  portions  of  the  limbs  reach 
the  cerebral  cortex,  as  do  also  those  coming  from  the  skin.  They  form 
in  the  cortex,  and  even  before  reaching  it,  numerous  associations. 
The  cortical  area  receiving  them  is  none  other  than  that  which  we  call 
the  tactile  area  situated  in  the  central  convolutions  of  the  Rolandie 
region. 

Several  proofs  may  be  given  of  this.  If,  as  Tonnini  has  done,  this 
region  in  animals  be  destroyed,  disturbances  of  the  muscular  sense  are 
invariably  observed.  If  the  limb  corresponding  to  the  region  destroyed 
be  placed  in  an  uncomfortable  position,  the  animal  retains  this  attitude 
without  troubling  to  alter  it.  which  it  would  do  at  once  if  it  had  any 
consciousness  of  this  discomfort,  that  is  to  say,  if  the  deep  sensibilities 
(above  all  muscular)  were  retained,  even  though  cutaneous  sensibility 
might  be  lacking.  Further,  disturbances  of  the  muscular  sense  are 
those  which  persist  the  longest  after  these  destructions,  as  a  number 
of  authors  have  observed. 

Dana,  in  view  of  svu"gieal  intervention,  liaving  laid  bare  tlie  middle  region  of 
the  right  ascending  frontal  convolution,  electrically  stimulated  tliis  region  of 
the  cortex  ;  contractions  of  the  left  arm  and  shoulder  ensued,  and  also  a  sen- 
sation of  swelling  and  of  heaviness  in  the  corresponding  limb.  The  stimula- 
tion produced  neither  pain  nor  a  feeling  of  contact,  but  a  sensation  which,  in 
our  opinion,  much  more  nearly  resembles  the  manifestations  of  muscular  or 
deep  sensibility.  It  must,  further,  be  recognized  that  in  this  observation  the 
succession  of  motor  and  sensory  effects  may  be  very  complicated,  and  that  it 
would  not  by  itself  point  out  to  us  the  locality  of  the  brain  in  which  are  situated 
the  cinsestliesic  impressions,  arising  from  the  movement,  whicli  evidently  results 
from  the  stimulation  of  the  cortex. 

Idea  of  the  movement  of  the  limbs. — By  these  different  sensibilities, 
and  especially  by  the  cinaesthesic  impressions,  we  obtain,  on  the  other 


TACTILE  INNERVATION  549 

hand,  the  idea  of  the  movement  of  our  hmbs.  This  movement  may 
be  either  passive  or  active. 

Passive  movement. — Passive  movement  is  a  more  or  less  abrupt 
change  of  the  position  of  our  hmbs  ;  we  appreciate  it  by  means  of  the 
same  sensory  elements  as  this  position  itself,  and  we  estimate  it  by 
the  change  supervening  in  the  impressions  which  these  elements  give 
rise  to. 

Active  movement. — In  active  movement  we  are  conscious,  not  only 
of  the  position  of  our  limbs  and  of  the  gradual  change  supervening  in 
this  position,  but  also  of  something  added  to  this,  namely,  a  jeeling  of 
effort. 

Sense  of  pressure  and  sense  of  force. — If  when  the  hand  is  extended 
with  its  dorsal  surface  on  a  resisting  plane,  we  place  on  its  palmar 
surface  gradually  increasing  weights,  we  can  estimate  within  certain 
limits,  the  absolute  and  relative  value  of  these  weights  ;  or,  to  put  it 
otherwise,  the  degree  of  pressure  (or  better),  compression,  exercised 
by  them.  If,  with  the  palm  of  the  free  hand,  we  weigh  these  weights, 
we  can  also  appreciate  their  value  ;  and  this  second  proceeding  will 
furnish  a  much  more  exact  estimation.  In  the  first  case,  our  resistance 
to  the  pressure  of  the  weights  is  purely  passive  and  the  stimulation  we 
receive  from  it  is  localized  in  the  cutaneous  sensibility  ;  in  the  second, 
certain  of  our  muscles  intervene  actively,  to  resist  the  pressure  of  the 
weights  and  to  balance  it  ;  the  muscular  sensibility  intervenes  con- 
jointly with  the  cutaneous  sensibility  to  give  us  the  appreciation  we 
are  in  search  of. 

3.  Feeling  of  effort. — Nothing  is  easier  to  verify,  but  nothing  more 
difficult  to  define,  to  analyse,  and  to  localize,  than  this  fact  of  internal 
observation.  Nevertheless,  it  is  quite  fundamental  ;  for  it  is  at  the 
origin  of  the  distinction  we  draw  between  ourselves  and  that  which 
is  external  to  us.  That  which,  from  the  beginning  of  our  existence, 
ajjpears  to  us  as  being  outside  ourselves,  that  which  resists  us,  or  which 
we  are  resisting.  By  the  external  forces  that  we  overcome,  that  we 
balance,  or  submit  to,  we  become  conscious  of  our  own  particular  force 
and  we  determine  the  plane  of  division  which  distinguishes  us  from 
them.  Effort  symbolizes,  by  an  elementary  example,  what  is  com- 
monly understood  under  the  name  of  activity,  another  term  of  which 
we  have  a  clear  conception,  but  which  it  is  quite  as  difficult  to 
define. 

The  value  of  effort,  so  far  as  it  concerns  the  fundamental  element  of 
the  formation  of  consciousness,  arises  from  the  close  association  and 
the  reciprocal  dependence  in  which  movement  and  sensation  are  here 
found  in  it,  a  dependence  and  association  which  arecharacteristic  of 


550  SPECIAL    INNERVATIONS 

the  living  being,  and  which  the  cycle  of  impulses  proceeding  from  the 
muscle  to  the  nervous  system  and  from  the  latter  to  the  muscle,  realizes 
in  the  most  direct  and  visible  manner.  From  it  arises  the  first  rough 
sketch  of  our  personality.  When  the  skin,  the  eye,  the  ear,  that  is  to 
say,  the  paths  of  the  senses  properly  so  called,  are  in  their  turn  open 
to  external  stimuli,  they  complete,  strengthen,  and  determine  precisely 
the  fundamental  ideas  provided  by  the  muscular  sense,  but  they  find 
these  essential  ideas  of  consciousness  already  constituted; 

Muscular  effort,  psychic  effort, — In  the  order  of  sensibility,  we  draw 
a  distinction  between  an  impression  made  at  the  periphery  and  a  sensa- 
tion which  does  not  develop  itself  clearly  except  in  the  superior  portions 
of  the  nervous  system.  In  the  order  of  sensibility,  we  distinguish  in 
the  same  way  between  a  purely  muscular  effort  which  is  exerted  by 
our  muscles  against  external  objects,  and  a  psychic  effort  proceeding 
from  the  superior  portions  of  the  same  system  in  order  to  arouse 
muscular  action.  We  will  consider  these  two  phenomena,  first  alone, 
then  as  regards  their  connexions. 

Analysis  of  the  phenomenon. — Taken  individually,  the  two  phenomena  of 
sensation  and  muscular  effort  may  at  once  be  pronounced  to  be  cyclic  pheno- 
mena. Sensation  implies  a  tendency  to  movement,  effected  more  or  less  feebly 
in  the  muscles  which  are  the  most  dii'ectly  in  connexion  with  the  surface  on 
which  the  impression  is  made  (adaptation  of  the  hand  to  the  sixrface)  of  the 
object  touched  (active  touch).  The  psychic  effort,  in  its  tiun,  implies  a  sensa- 
tion immediately  consecutive  to  the  movement  jDroduced  (sensation  of  muscular 
activity,  of  displacement  of  the  osseous  levers  and  their  soft  parts,  resistance 
of  raised  weights,  etc.).  We  here  find  once  again  the  double  reciprocal  link 
between  sensibilitj^  and  movement — a  link  of  such  a  nature  that,  were  it  to  be 
completely  broken,  it  may  be  assmned  that  neither  sensibility,  nor  effort,  nor 
any  nervous  functional  act,  would  any  longer  be  possible. 

The  analysis  may  be  carried  still  further.  If  we  cut  away  and  destroj'  the 
superior  systems,  sensation  and  iisychic  effort,  properly  so  called,  disappear, 
and  are  replaced  by  reflex  acts  which  only  represent  them  in  an  extremely 
attenuated  form.  Yet  in  these  reflex  acts  we  find,  once  more,  the  same  double 
link,  between  sensibility  and  movement.  From  the  fact  of  the  existence  of  this 
link  certain  reflex  acts  acquire  the  possibility  of  subsisting  automatically  in  an 
indefinite  manner  when  movement  has  once  begun  in  them  (respiration,  regula- 
tion of  the  nutritive  functions).  If  we  disorganize  the  interior  systems  by 
cutting  the  peripheral  nerves,  sensation  does  not  irrevocably  disappear,  but  naay 
be  prolonged  and  reawakened  in  the  condition  of  remembrance  ;  the  cerebral 
phenomenon,  thus  unloosed  from  its  connexions  with  external  provocative 
actions,  takes  the  name  of  psychic  ;  it  is  certainly  connected  with  the  persist- 
ence of  internal  reflex  cycles  which  preserve  the  impulse  and  prolong  the  sensa- 
tion in  a  manner  which  is  fundamentally  automatic.  In  an  individual  whose 
brain  is  intact,  but  whose  spinal  motor  nerves  are  paralysed,  the  psychic  effort 
is  still  possible.  Svich  an  individual  has  a  very  distinct  representation  of  the 
movements  which  he  wishes  to  execute,  but  which  he  is  j^revented  from  per- 
forming by  his  peripheral  paralysis.  It  must  be  assumed  that,  in  this  case 
also,  the  cerebral  process  is  of  a  psychic  form  :  to  the  descending  impulses 
which  leave  the  cortex  and  which  are  not  stopped  in  their  journey-  before  reach- 


TACTILE  INNERVATION  '  551 

ing  the  muscles,  succeed  others  which  ascend  to  it  by  reflexion  of  the  first  on: 
the  subjacent  centres,  and  bring  into  action  the  nervous  mechanism  in  all  that 
is  essential.  Reflexion,  with  recall  of  precise  sensations  and  definite  representa- 
tions of  movements  (but  without  actual  impressions  as  regards  the  first,  or 
execution  as  concerns  the  second),  can  only  be  rationally  explained  by  a  y>to- 
cess  of  this  natxire,  a  process  made  in  the  likeness  of  that  which  brings  actual 
sensation  and  voluntary  movement  into  being,  but  which  is  confined  to  the 
superior  portions  of  the  nervous  system,  and  is  for  this  reason  piu-ely  repre- 
sentative. 

4.  Voluntary  stimulation, — ^When  movement  follows  immediately 
on  an  unconscious  impression,  we  call  it  reflex  ;  when  it  follows  in- 
evitably a  vividly  felt  impression,  we  call  it  psycho-reflex  or  emo- 
tional ;  when  it  has  no  connexion  with  a  stimulus  or  an  actual  sensa- 
tion, we  call  it  spontaneous  or  voluntary. 

Movement  appears  to  us  to  be  here  independent  of  sensation,  and 
the  dissociation  of  these  two  phenomena  seems  complete.  It  is  so  only 
in  appearance  however.  Voluntary  determination  arises  from  ideation, 
from  reflexion,  and  this  in  its  turn  proceeds  from  sensation.  But 
the  determination  which  we  call  voluntary  has  about  it  this  peculiarity  : 
that,  while  keejnng  its  connexion  with  sensation,  it  may  be  adjourned  in 
time  in  an  indefinite  manner  ;  and  as,  during  this  delay,  the  brain 
receives  new  impulses,  which  it  has  the  power  of  preserving  auto- 
matically, and  is  also  capable  of  associating  and  reassociating  in 
numerically  infinite  combinations,  the  postponement  of  the  move- 
ment, as  well  as  its  extreme  variety,  disguises  its  true  origin,  which 
can  only  be  in  an  external  stimulus. 

Thus  the  will  does  not  reveal  a  spontaneity  of  impulses,  but  a  very 
profound  transformation  of  them  in  their  passage  through  the  brain,, 
a  transformation  in  virtue  of  which  they  are  mutually  associated  in 
the  whole  compass  of  this  organ  and  may  also  be  connected  in  time. 
Hence  there  results,  as  regards  the  individual,  a  sort  of  appropriation 
of  the  objects  surrounding  him,  which  he  condenses  in  himself  under 
the  form  of  representations  ;  there  also  results  for  him  a  number  of 
motor  possibilities  in  a  way  almost  unlimited  and  practically  a  great 
power  over  these  same  objects.  The  sentiment  of  motor  spontaneity 
existing  in  us  has  its  origin  in  a  process  of  internal  analysis  which 
compares  these  different  motor  possibilities  between  themselves,  and 
which,  by  foretelling  their  consequences,  gives  a  preference  to  one  of 
them,  after  a  series  of  mental  experiments  which  are  not  followed  by 
action.  Without  hesitation,  we  should  not  know  the  meaning  of  the 
will.  Reflex  action  narrowly  resembles  a  physically  determined 
movement  ;  it  acts  without  hesitation,  that  is  to  say,  without  delay  ; 
voluntary  effort  is  a  movement  which  is  at  the  same  time  physically 


552  SPECIAL    INNERVATIONS 

and  psychically  determined,  that  is  to  say,  in  which  the  determinism 
is  present  in  several  degrees. 

Sensation  and  movement  in  the  foetus. — The  foetus,  wliile  still  m  utero,  exerts 
movements  which  are  known  as  active  and  which  are  regarded  as  spontaneous. 
When  the  origin  of  these  movements  is  taken  into  account,  it  will  be  obvious 
that  they  would  be  more  accurately  described  as  reflex.  In  the  first  instance, 
the  foetus  seems  to  be  protected  against  every  external  excitation  by  the 
maternal  organs  ;  this  is  certainly  true  so  far  as  regards  merely  shock  from 
external  objects  and  the  specific  excitants  of  the  senses  (light,  sound,  etc.)- 
But  the  structure  which  encloses  and  protects  the  foetus  (the  uterine  muscle) 
is  also  cajoable  of  exciting  it  by  its  contractions  and  by  the  pressures  which 
result  therefrom.  It  would  seem,  therefore,  to  be  quite  reasonable  to  main- 
tain, with  Fere,  that  the  movements  of  the  foetus  are  merely  the  reaction  of 
its  nervous  system  against  uterine  contractions  ;  and  that,  whatever  may  be 
the  degree  of  consciousness  with  which  they  are  accompanied  from  their  first 
appearance  vip  to  the  moment  of  birth,  their  reflex  origin  cannot  be  denied. 

Reactions  of  the  uterus  to  excitations  proceeding  from  the  different  senses.— 
Like  all  other  visceral  movements,  the  contractions  of  the  uterus  (during  preg- 
nancy) are  not  perceived  by  the  mother  ;  as  a  matter  of  fact,  these  excitations 
frequently  occiu",  and  are  the  result,  like  those  of  the  vessels,  of  the  intestine, 
of  the  bladder,  etc.,  of  every  somewhat  marked  excitation  of  any  one  of  the 
senses.  It  is  a  fact  well  known  to  all  those  who  are  in  the  habit  of  performing 
experiments,  that  such  excitations  react  on  all  these  organs,  giving  rise  to  con- 
tractions, in  them,  even  apart  from  their  functional  activity  properly  so  called. 
The  uterus  forms  no  exception  to  this  rule  ;  it  is  these  contractions  to  which 
the  foetus  is  subjected,  and  which  furnish  it  with  the  first  idea  of  that  which 
■exists  external  to  itself.  Hence  there  are  reflex  movements  of  the  fcetus  con- 
secutive to  maternal  uterine  reflexes.  It  follows  therefore  that  the  origin  of 
foetal  movement  is  invariably  an  external  excitation  ;  this  excitation  must  pass 
through  the  maternal  nervous  system  before  it  can  attain  its  own  special  nervous 
■system,  exactly  as  its  nutritive  materials  pass  through  the  maternal  blood  before 
entering  its  own.  All  the  specific  excitations  which  affect  the  maternal  senses 
are  thus  transformed  and  brought  back  to  almost  uniforin  inechanical  excita- 
tions, which  act  on  the  foetus,  and  through  them  it  receives  its  first  lessons  as 
regards  sensation. 


CHAPTER  II 
VISUAL    INNERVATION 

Like  touch,  with  which  it  has  so  many  points  of  resemblance  and  so 
many  connexions,  vision  is  a  phenomenon  which  is  at  the  same  time 
both  passive  and  active.  We  see  the  objects  which  present  themselves 
to  us  ;  further,  we  look  at  those  which  our  attention  points  out  to  us. 
The  motor  and  sensory  acts  succeed  each  other  as  it  were  in  cycles, 
which  the  intervention  of  the  other  senses  complicates  and  enlarges 
in  proportion  as  it  augments  the  sources  of  our  knowledge. 

The  sensori-motor  system  appropriated  to  the  sense  of  sight  com- 
prehends (like  all  other  systems  of  the  same  nature)  :  at  its  origin, 
differentiated  receptive  elements,  the  rods  and  the  cones,  adapted  for 
the  reception  of  luminous  impulses  ;  at  its  termination,  muscles  which 
turn  the  eye  towards  that  locality  in  space  to  which  it  is  directed  in 
order  to  seek  this  stimulus  :  between  the  former  and  the  latter  are 
reflex  arcs,  whose  complexity  goes  on  increasing  with  their  length, 
causing  the  impulse  to  penetrate  more  deeply,  from  the  retina  up  to 
the  cerebral  cortex.  It  is  the  constitution  of  these  arcs,  infinitely 
variable  according  to  the  case  under  consideration,  which  forms  the 
basis  of  the  study  of  visual  innervation.  On  the  surface  of  the  brain 
an  area  may  be  approximately  delimited  which  represents  the  deepest 
locality  where  these  impulses  are  reflected,  a  kind  of  surface  of  projec- 
tion which  they  only  attain  when  they  are  to  become  conscious  (visual 
area  of  the  cortex  distinct  from  that  of  the  other  senses).  At  the 
periphery  a  still  more  distinctly  defined  field,  that  of  the  two  retinae, 
represents  the  surface  of  reception  for  luminous  impulses  ;  as  for  the 
muscles  to  which  the  stimulation  returns,  these  in  principle  may  be 
all  the  muscles  of  the  body,  but  as  we  are  concerned  with  the  analysis 
of  the  phenomenon,  we  will  specially  consider  those  directing  the 
visual  axes,  namely  :  the  rotatory  muscles  of  the  eye,  the  head,  or 
even  of  the  body. 

From  the  retina  to  the  brain  the  impulses  traverse,  or  coast  along, 
certain  localities  of  the  grey  matter,  which  may  send  them  back  un- 
consciously to  the  protective  muscles  of  the  eye,  or  to  certain  internal 


554  SPECIAL    INNERVATIONS 

muscles,  which  also  exert  protective  functions  and  those  of  adaptation 
for  this  organ  as  regards  the  luminous  agent. 

A.  FROM  THE  RETINA  TO  THE  CEREBRAL  CORTEX 

The  retina,  a  thin  membrane  which  carpets  the  deep  portion  of  the 
eye,  presents  in  its  thickness  three  superposed  neurons  (more  exactly, 
two  neurons  and  a  portion  of  a  third).  These  are  :  (1)  the  rods  and 
the  cones  (the  last  in  the  yellow  spot  and  the  first  in  the  rest  of  the 
membrane)  ;  (2)  the  bipolar  cells  known  as  visual ;  (3)  the  cells  known 
as  ganglionic.  These  last  give  rise  to  axons  which  form  the  fibres  of 
the  optic  nerve  and  ascend  towards  the  cortex. 

1.  Morphological  signification. — As  regards  the  whole  of  the  sensori- 
motor systems  into  which  the  nervous  system  is  divided,  a  unity  of 
plan  is  admitted  as  also  a  sort  of  equivalency  between  their  component 
elements.  In  the  series  of  neurons  forming  each  of  these  partial  systems 
it  may  readily  be  allowed  that  there  exists  the  same  number  of  elements 
and  principal  halting  places  passed  over  by  the  impulse.  We  may 
then  attempt  to  group  these  in  numerical  order,  by  comparison  of  one 
system  with  another.  In  the  tactile  system  the  initial  neuron  is  that 
which,  from  the  skin,  proceeds  to  the  grey  medullary  matter,  where 
the  impulse  is  taken  up  by  a  second  neuron  which  reaches  the  ence- 
phalon.  In  the  visual  system,  the  initial  neuron  is  a  rod  or  a  cone 
which  transmits  the  impulse  to  a  bipolar  cell  ;  this,  in  its  turn,  passes 
it  on  to  a  ganglionic  cell  or  to  the  origin  of  the  optic  nerve.  Thus  it  is 
tolerably  clear  that  another  element  exists,  over  and  above  that  con- 
tained in  the  preceding  system,  taken  as  a  type  of  structure.  An 
effort  has  been  made  to  re-establish  homology  by  comparing  the  rod 
and  the  cone,  no  longer  to  a  nervous  element,  but  to  a  differentiated 
epithelial  cell  resembling  those  w^iich  are  found  at  the  extremity  of  the 
nervous  tactile  terminations  ;  in  this  case  the  equivalents  of  the  neurons 
of  the  posterior  roots  would  be  the  bipolar  cells.  If  an  intravascular 
injection  of  methylene  blue  be  made  on  the  living  animal,  the  rods 
and  the  cones  will  undergo  no  coloration,  while  the  bipolar  cells  and 
all  the  strictly  nervous  elements  of  the  retina  will  be  coloured  by  this 
reagent  (Renaut). 

Fundamentally,  it  must  be  admitted  that,  in  all  these  systems,  we 
do  not  know  the  exact  mutual  connexions  of  the  nerve  elements.  We 
are  ignorant  whether  there  may  not  exist,  between  the  first  and  second 
tactile  neurons,  some  short  interposed  neuron  of  the  same  nature  as 
the  bipolar  cell  of  the  retina.  And,  further,  the  unity  of  plan  may  not 
be  of  so  rigid  a  nature  as  to  imply  a  number  of  exactly  similar  elements 
in  all  the  analogous  systems. 


VISUAL    INNERVATION 


555 


Cells  of  association. — Besides  the  neurons  Avhicli  seem  thus  to  be 
placed  in  direct  succession  to  each  other,  cells  exist  either  in  the  spinal 
cord  or  in  the  retina,  which  are  provided  with  short  prolongations  ; 
these  are  called  cells  of  the  neurons  of  association,  because  it  is  sup- 
posed that  they  establish  between  the  nervous  conducting  paths  rela- 
tions other  than  those  arising  from  the  direct  contact  of  these  last- 
named.  A  knowledge  of  the  manner  in  which  these  associations  are 
carried  out  would  be  of  the  very  highest  interest  to  us,  but  at  present 
this  information  is  wanting.  We  can  but  suppose  the  connexion  to 
be  of  a  very  complicated  nature.  In  the  layer  of  the  internal  granules 
of  the  retina  are  found  small  and  large  horizontal  cells  to  which  a 
function  of  this  description  has  been  assigned.  Other  cells  called 
spongiohl  asts 
have  also  been 
observed 
whose  single 
expansions  are 
connect  e  d 
with  the  gang- 
lionic cells  of 
the  retina. 
The  retina, 
while  present- 
ing abbre- 
viated struc- 
tures, which 
elsewhere  at- 
tain  large 
dime  n  s  i  o  n  s, 
is,  neverthe- 
less, a  more 
CO  n  V  e  n  i  e  n  t 
locality  than 
are  those 
others  for  the 
study  of  the 
cpnnexi  on  s 
under  discus- 
sion. More  particularly,  it  displays  the  following  detail,  also  ob- 
servable in  other  senses,  namely  :  that  in  their  articulation,  the 
neurons  do  not  correspond  each  to  each,  but  that  their  field  of 
distribution  overlaps  portions  (it  may  be  unequal  portions,  according 


Fig.  228. — The  retina  (diagram,  after  M.  Duval). 

1  to  9,  the  iiine  layers  of  the  retina  ;  I,  II,  III,  the  three  superposed 
neurons  which  form  its  elements  placed  in  succession  ;  I,  visual  cells  ;  II, 
bipolar  cells  ;  III,  ganglionic  cells  ;  CH  and  SP,  neurons  of  association  ; 
CH,  small  horizontal  cell;  CHo,  large  horizontal  cell;  SPtoSP5,.the 
five  orders  of  spongioblasts. 


556  SPECIAL    INNERVATIONS 

to  circumstances)  of  the  fields  of  reception  of  the  consecutive  neurons. 

2.  The  retina  is  a  nervous  centre. — However  it  may  be  with  regard 
to  these  details,  we  must  conclude  that  the  retina,  speaking  generally, 
is  the  equivalent  of  the  grey  hulho-medullary  matter.  It  should  be  regarded 
as  a  portion  of  this  matter  separated  from  the  rest,  and  brought  during 
its  development  into  the  vicinity  of  the  periphery.  The  optic  nerve 
is  not  the  equivalent  of  a  posterior  medullary  root,  but  rather  of  a 
white  tract  of  the  spinal  cord,  which  has  become  involved  in  the  orbit 
for  the  purpose  of  uniting  the  grey  retinal  matter  to  the  encephalic 
centres  (ganglionic  and  cortical). 

Gradation  of  the  grey  masses. — The  fibres  of  the  optic  nerve,  after 
having  passed  through  the  chiasma,  are  found  (some  after  dissociation 
and  others  directly)  in  the  optic  tracts,  and  these  end  in  three  very 
remarkable  localities  of  the  grey  matter  :  the  external  geniculate  body, 
the  anterior  corpus  quadrigeminum,  the  pulvinar  of  the  optic  thalamus. 
This  latter  gives  its  significance  to  these  centres  as  a  whole.  The 
ganglia  of  the  base  of  the  brain,  and  especially  the  optic  thalamus,  are, 
as  is  now  known,  the  principal  terminations  of  the  conducting  paths 
of  sensation,  both  general,  tactile  and  sensorial. 

The  optic  thalamus  is  divided  into  segments,  of  which  each  answers 
to  a  determinate  area  of  the  cerebral  cortex  (Monakow)  ;  the  pulvinar 
represents  the  segment  corresponding  to  the  occipital  lobe  and  apper- 
taining to  vision. 

The  pulvinar,  the  corpus  quadrigeminum  and  the  external  geniculate 
body  are  often  described  by  the  name  of  primary  centres  of  vision. 
This  designation  should  be  rejected,  inasmuch  as  this  stage  of  the  grey 
matter  is  really  the  second,  the  retina  being  obviously  the  first. 

3.  Optic  radiations. — From  the  ganglia  of  the  base  of  the  brain  the 
impulse  (whether  it  passes  through  them  or  only  skirts  along  them) 
becomes  involved  in  the  fibres  which  conduct  it  up  to  the  cortex,  to 
an  area  thereof  occupying  the  borders  of  the  calcarine  fissure.  These 
fibres  form  the  optic  radiations  or  those  of  Gratiolet  ;  they  arise  in  an 
intricate  mass  of  fibres  (field  of  Wernicke)  confined  to  the  pulvinar, 
and,  skirting  more  especially  the  internal  surface  of  the  posterior  horn 
of  the  lateral  ventricle,  spread  themselves  out  in  the  cortex  on  the 
internal  surface  of  this  lobe. 

Long  paths  and  interrupted  paths. — The  same  question  which  has 
already  arisen  as  regards  the  other  senses  once  more  confronts  us  here. 
What  is  the  value  and  signification  of  these  different  stages  of  the  grey 
matter  ?  What  is  the  choice  here  effected  between  the  conducting 
elements  ?  And  what  connexions  are  here  entered  into  by  them  with 
the  new  elements  arising  in  it  ? 


VISUAL    INNERVATION 


557 


In  principle,  we  know  that  the  impulse  here  finds  paths  of  return, 
which  bring  it  back  to  the  motor  organs  endowed  with  psychical 
qualities,  but  with  less  of  these  in  proportion  to  the  shortness  of  the 
reflex  arc  ;  that  is  to  say,  in  proportion  as  the  reflex  arc  is  less  involved 
in  the  depths.  But  this  is  not  sufficient.  The  impulses  which  are  not 
reflected,  but,  on 
the  contrary,  con- 
veyed towards  the 
cortex,  also  seem 
to  undergo  a  trans- 
formation therein, 
whose  modalities 
and  precise  mech- 
anism escape  us. 

Anatomy  mereh' 
demonstrates  this : 
of  these  halting 
places  of  the  grey 
matter,  the  first 
represent  c  o  m- 
p  1  e  t  e  interrup- 
tions, all  the  fibres 
ending  therein  to 
re-arise,  following 
new  connexions  ; 
the  retina  and 
the  grey  medul- 
lary matter  are 
halting  places  of 
this  kind;  the 
second  are  only 
partial     interrup- 


FiG.   -229. — The  \isual  system  :  its  sensorial  paths  (diagram 

copied  from  Vialet). 
T+ie  cuneus,  the  pulvinar,  the  corpus  quadrigeminum,  the  external 
geniculate  body  and  the  half  retina  of    the  left  side  are  marked  by 


tionS,  a  part  of  the  hatching,  and  also  the  portion  of  the  visual  area  of  each  eye  corre- 
rji  /J"    ^    n      i.-  sponcUng  to  them. 

riDreS    CllStribUtnig         Associating  tracts  miite  the  occipital  lol)e    and  the  angular  gyrus 
their      terminal    ^"  ^^^  convolutions  of  the  area  of  speecli.  and  in  the  latter  the  first 
temporal  to  the  third  frontal. 

arborizations 

there,  while  the  rest  pass  through  them  without  solution  of  con- 
tinuity to  terminate  in  some  other  grey  nervous  mass.  The  pul- 
vinar, the  corpora  quadrigemina,  the  geniculate  bodies,  all  the  basal 
gangha,  are  included  in  this  category.  The  grey  bulbo-medullary 
axis  (with  its  sensorial  equivalents)  and  the  cerebral  cortex  would 
thus  be  the  two  localities  where  the  grey  matter  would  have  its  most 


558  SPECIAL    INNERVATIONS 

marked  morphological  character.  This,  however,  is  only  a  question 
of  degree,  since  the  boundary  line  of  these  areas  and  their  distinction 
from  the  white  matter  are  not  in  the  least  absolute.  However  this 
may  be,  some  maintain  the  possibility  of  the  existence  of  fibres  (in 
small  numbers)  going  directly  from  the  retina  to  the  cortex,  skirting 
the  intermediate  centres  ;  these  are  the  long  or  direct  paths  ;  the  other 
conducting  fibres  are  arrested  and  arranged  in  series  in  these  different 
centres,  or  else  associate  them  amongst  themselves  ;  by  comparison 
with  the  others,  they  are  short  paths  which,  as  a  whole,  may  be  called 
interrupted  paths  in  opposition  to  the  preceding. 

4.  Progressive  transformations  of  the  nervous  act. — The  problem  is 
no  longer,  as  has  for  a  long  time  been  imagined,  to  find  some  sort  of  a 
path  which  would  either  by  itself  alone,  or  by  the  union  of  its  con- 
tiguous segments,  project  the  impulse  received  at  the  periphery  on  to 
the  cerebral  cortex,  this  definitely  giving  to  the  nervous  act  its  psychi- 
cal qualities.  Everything,  on  the  contrary,  tends  to  prove  that  these 
qualities  are  only  acquired  progressively,  by  successive  processes, 
leaving  nothing  for  the  cortex  but  a  completion  of  the  work  by  utilizing 
elements  which  have  been  previously  elaborated.  What  is  the  part 
played  by  the  short  and  interrupted,  or  long  and  direct  paths  in  this 
preparatory  process  ?  To  this  question  the  facts  at  present  at  our 
disposal  do  not  provide  us  with  a  satisfactory  answer.  Are  these  paths 
employed  separately  for  distinct  functional  acts  ;  and,  if  so,  for  which  ? 
Or  are  they  employed  simultaneously  in  the  most  complicated  aggre- 
gated acts  ?  These  also  are  questions  to  which  no  answer  can  be  given, 
but  which  it  is  necessary  for  us  to  propound. 

5.  Dispersion  of  the  impulses  in  the  system. — The  succession  of  im- 
pulses following  the  nervous  paths  from  the  retina  up  to  the  cortex  is 
thus  known  to  us  as  regards  its  general  direction,  and  even  as  concerns 
its  multiple  paths  of  return  towards  the  periphery,  as  will  be  explained 
farther  on.  In  proportion  to  the  progress  made  by  it  in  the  deep 
portions  of  the  system,  it  undergoes  divisions  or  predetermined  orienta- 
tion in  the  more  and  more  numerous  paths  opening  out  before  it.  The 
reflex  arc,  which  is  the  form  taken  by  the  journey  as  a  whole,  not  only 
presents  gradations,  but  also  undergoes  interruptions  in  its  length  ; 
these,  however,  not  being  total  but  segmentary,  and  more  numerous 
as  the  cortex  is  approached,  towards  and  in  which  everything  attains 
its  maximum  of  complexity.  The  pulvinar,  the  geniculate  body,  the 
corpus  quadrigeminum  all  correspond  to  breaks  of  this  nature,  destined 
for  the  adaptation  of  the  luminous  and  visual  impulse  to  its  very  varied 
functions.  They  are  analogous,  but  not  identical  parts,  and  thus  cannot 
completely  supply  each  other's  place.     Of  these  three  grey  masses,  the 


VISUAL    INNERVATION 


559 


one  most  essential  for  the  transmission  to  the  cortex  of  luminous  im- 
pulses is  the  geniculate  body  (Gratiolet). 

The  cells  of  this  ganglion  are  so  arranged  that,  for  the  most  part, 
their  axis  cylinders  are  orientated  towards  the  brain,  thus  indicating 
that  the  progress  of  the  impulse  proceeds  from  the  geniculate  body 
to  the  cortex  (Monakow). 

We  are  unaccj[uainted  with  the  existence  of  any  fibres  bringing  back 
the  impulse  from  the  geniculate  body  towards  the  motor  periphery  ; 
this,  how^ever,  being  assuredly  no  proof  of  their  non-existence.  On 
the  contrary,  w^e 
know  of  some 
which,  from  the 
other  ganglia,  and 
especially  from 
the  corpus  quadri- 
geminum,  reflect 
the  impulse  on  the 
motor  organs  ;  for  * 
example,  the  irido-  ' 
pupillary  reflex. _^ 

r     ^  -'  '■  ^_- — ^    i^sfx-ws      1  Gen.  body 


Cerebral,  cert. 


Retina 


Pu'vinar 


...  Corp.  quad. 


....F.  1.2). 


Mot.  mid. 


Fig.  230.— Ganglionic  optic  paths  (diagram). 


Functional  and 
evolutional  balance. 
— If  we  examine  the 
development  of  the 
grey  s  u  b-c  ortical 
masses  in  the  verte- 
brate series,  it  will  be 
seen  that  this  de- 
velopment is,  as  re- 
gards some,  in  inverse 
ratio  to  that  of  the  cor- 
tex, and  as  regards 
others,  in  direct  ratio  to  its  development.  Specifically,  the  bigeminal  tubercule  (optic 
lobe)  follows  the  first  covirse  ;  the  external  geniculate  body  and  the  pulvinar 
follow  the  second  (Edinger,  Forel,  Monakow).  The  quackigeminal,  or  bigeminal 
tubercule  (optic  lobe),  forms  one  system  ;  the  cortex  of  the  hemispheres,  the 
pulvinar,  and  the  geniculate  body  form  another.  The  first  is  the  oldest  of  these 
two  systems ;  that  is  to  say,  that  it  can  exist  alone,  and  discharge  (with  the 
similar  organs  of  the  other  senses)  the  rudimentary  psychical  functions  of  in- 
ferior animals  ;  it  is  thus  that  in  certain  fish  the  pallium  does  not  yet  exist, 
and  is  represented  by.  an  epithelial  layer  which  covers  the  ventricles.  The 
second,  in  proportion  as  it  is  more  highly  develojaed,  and  as  intelligence  takes 
the  place  of  instinct,  deprives  the  former  of  its  functions  (whence  arises  atrophy 
of  the  optic  lobes,  which  are  replaced  in  mammals  by  the  corpora  quadrigemina), 
and  becomes  augmented  both  in  its  cortical  and  ganglionic  portions  (whence 
the  development  of  the  pulvinar  and  the  geniciilate  body  in  mammals). 

In  reality  this  division  is  not  so  markedly  schematic  inasmuch  as  a  portion  of 


560  SPECIAL    INNERVATIONS 

the  optic  tlialaiiius,  and  even  of  the  geniculate  body,  appertains  to  the  first 
system  (primary  system,  whose  function  is  reflex).  As  the  intellectual  system 
develops  it  reduces  a  portion  of  this  whole,  principally  the  bigeminal  tubercule 
(optic  lobe),  while  it  increases  the  other  portion  (optic  thalamus  and  geniculate 
body)  by  the  prolongations  which  the  pallium  conveys  to  it  throvigh  its  own 
development. 

The  study  of  degenerations  also  supports  this  conception.  After  the  removal 
of  the  cortex  all  these  masses  display  degenerated  fibres  alongside  of  healthy 
ones,  but  the  relative  proportion  of  the  two  is  then  very  different.  The  anterior 
corpus  quadrigeminum  remains  almost  healthy,  but  the  optic  thalamus  shows 
extensive  degeneration  at  the  level  of  the  pulvinar,  and  the  external  geniculate 
body  is  almost  completely  invaded  by  this  degeneration. 

Functional  distinctions. — By  the  help  of  the  actual  information  afforded  us 
by  physiology  and  clinical  surgery,  an  effort  has  been  made  to  establish  fvmc- 
tional  distinctions  between  these  three  morphologically  remarkable  grey  masses 
— the  anterior  corpus  quadrigeminum,  the  optic  thalamus,  and  the  external 
geniculate  body  ;  and,  with  this  end  in  view,  the  following  differences  are 
brought  forward.  The  fii'st  of  these  centres  is  purely  reflex,  and  it  throws  back 
the  impulses  it  has  received  on  to  the  intra-ocular  or  peri-ocular  muscles.  The 
second  is  a  centre  for  reflexes  of  instinctive  order,  by  which  emotions  are  re- 
vealed (movements  of  the  eyes  and  the  face,  mimicry  expressive  of  the  emotional 
sensations  received  by  the  eye).  The  third,  unlike  the  two  others,  instead  of 
bringing  back  the  retinal  impulses  directly  to  the  motor  paths,  on  the  contrarj", 
involves  them  still  more  deeply  in  the  brain,  and  by  the  optic  radiations  con- 
veys them  to  the  cerebral  cortex,  where  they  give  rise  to  distinct  sensation, 
to  the  formation  of  an  image,  and  finally  to  the  idea  preserved  in  a  state  of 
remembrance  before  being  revealed  by  a  motor  act. 

Isolated  lesions  of  these  three  grey  masses,  if  it  were  possible  to  realize  them 
or  to  meet  with  them  absolutely  localized,  wovild  be  rendered  evident  by  the 
isolated  abolition  of  each  of  these  three  forms  of  reaction,  namely,  as  regards  the 
corpus  quadrigeminum,  loss  of  the  inferior  reflexes  ;  the  optic  thalamus,  that 
of  emotional  expression  ;  the  external  geniculate  body,  loss  of  the  capability 
of  awakening  visual  sensations,  but  at  the  same  time  with  conservation  of  the 
images  and  ideas  previously  formed,  so  long  as  the  visual  cortex,  with  the 
connexions  vmiting  it  to  the  other  senses,  is  still  preserved. 

Comparative  visual  physiology. — This  classification  is  not  applicable  as  such 
to  the  whole  series  of  the  \ertebrata.  The  lower  we  descend  in  the  scale  tlie 
greater  is  the  importance  assruned  by  the  sub-cortical  centres  relatively  to  the 
cortex,  whose  functions  they  more  or  less  share.  Conversely,  the  higher  we 
ascend  the  more  we  see  the  cortex  monopolizing  the  functions  of  these  grey 
masses,  but  at  the  same  time  differentiating  and  improving  them  in  a  singular 
manner.  At  the  summit  of  the  series  many  purelj^  reflex  acts  have  become 
instinctive,  and  instinctive  acts  intelligent.  The  organs  subserving  reflex  and 
instinctive  acts  persist,  but  they  discharge  less  important  functions,  and  this 
not  merely  from  a  relative,  but  also  from  an  absolute  point  of  view. 

B.     THE  RETINAL  IMAGE.     RODS  AND  CONES 

The  longitudinal  cleavage  of  the  visual  system  begins  at  the  surface 
of  the  retina  which  receives  the  luminous  excitations.  In  fact,  the 
retinal  field  is  divided  into  two  very  unequal  portions  :  one  central, 
being  the  ijdlow  spot  containing  the  cones  ;  the  other  peripheral, 
containing  more  especially  the  roJs. 


VISUAL    INNERVATION  561 

1.  Functional  differences. — Max  Schultze,  owing  to  certain  indica- 
tions yielded  by  anatomy  and  comparative  physiology,  believed  that 
the  rods  are  connected  with  luminous  perceptions  and  the  cones  with 
the  perception  of  colours.  Parinaud  has  rendered  this  connexion 
more  precise,  and  has  studied  the  mechanism  of  these  functional  differ- 
ences. The  human  retina,  he  remarks,  is  formed  as  it  were  of  two 
associated  rctince  ;  that  of  the  cones  and  that  of  the  rods.  The  former 
yields  the  sensation  of  light  and  darkness  ;  and,  further,  all  the  colour 
sensations.  The  second  only  supplies  the  sensations  of  light  and 
darkness  ;  from  this  point  of  view  it  is  less  perfect  than  the  preceding, 
but  this  imperfection  is  compensated  by  another  quality.  As  twilight 
approaches,  or  when  darkness  is  artificially  procured,  this  retina  con- 
taining the  rods  has  the  power  of  adapting  itself  to  a  very  feeble  illu- 
mination and  enables  us  to  recognize  the  objects  around  us.  In  hemera- 
lopics  who  have  lost  the  power  of  seeing  in  a  feeble  light  it  is  this 
retina  which  no  longer  fulfils  its  function.  As  v.  Kries  has  also 
observed,  the  cones  are  an  apparatus  adapted  for  strong  light,  and  the 
rods  for  partial  obscurity.  In  total  daltonism  (congenital)  the  opposite 
is  the  case  ;  the  cones  being  impaired,  the  perception  of  colours  no 
longer  exists,  but  as  the  rods  are  intact  the  perception  of  light  is  still 
preserved. 

Retinal  visual  purple. — The  rods  are  found  almost  exclusively  in 
the  retina  of  nocturnal  animals  (owls,  bats,  hedgehogs)  ;  in  most  birds 
the  cones  predominate  or  are  alone  present.  The  adaptation  of  the 
perimacular  region  of  the  retina,  or  of  the  rods,  to  very  feeble  illumina- 
tion must  be  connected  with  the  presence  of  the  retinal  visual  purple, 
or  rhodopsin,  which  is  absent  in  the  macular  retina  or  the  cones.  This 
substance,  which  is  easily  decomposable  by  light,  is  fluorescent,  or,  in 
other  words,  it  absorbs  certain  rays,  principally  the  invisible  chemical 
rays,  and  transforms  them  into  visible  rays,  thus  augmenting  the 
illumination  of  the  retina. 

The  region  of  the  macula  lutea  possesses  one  other  function  which 
distinguishes  it  from  the  area  surrounding  it.  The  image  of  the  objects 
we  are  looking  at  is  thrown  on  the  fovea  centralis,  and  this  image  is 
here  more  distinct  than  in  the  rest  of  the  retina  ;  the  absence  of  visual 
purple,  and  therefore  of  fluorescence,  helps  to  give  it  this  distinctness. 
Thus  the  cones  play  the  principal  part  in  the  performance  of  the  retinal 
functions,  possessing  as  they  do  the  faculty  of  differentiating  luminous 
impressions  which  are  geometrically  distinct,  whence  results  the  per- 
ception of  forms,  or  visual  acuity  properly  so  called  (Parinaud).  It 
must  also  be  observed  that  each  cone  is  connected  with  a  bipolar  cell, 
while  each  bipolar  cell  is  connected  with  several  rods.     In  the  yellow 

P.  0  0 


562  SPECIAL    INNERVATIONS 

spot,  the  cones  are  not  only  solitary,  but  are  also  very  small  and  closely 
pressed  against  each  other  ;  their  diameter  is  about  0002mm.  to 
0-0025mm.  (Schultze).  But  the  shortest  distances  betAveen  two  retinal 
images  which  can  be  distinguished  from  each  other  are  from  00043mm. 
to  0-0054mm.  (E.Weber,  Helmholtz),  or,  by  practice,  0003mm.  (Volk- 
mann),  this  figure  approaching  that  of  the  diameter  of  the  cones  and, 
by  comparison  with  it,  explaining  to  us  the  limits  of  distinct  vision. 

2.  Macular  and  peri-macular  tract. — The  jovea  centralis  is  connected 
with  a  distinct  tract  of  the  optic  nerve,  which  may  be  followed  along 
the  whole  course  of  the  latter.  This  is  the  macular  tract,  and  a  section 
of  the  optic  nerve  (near  to  the  ball  of  the  eye)  closely  resembles  the 
arrangement  which  holds  in  the  retina  and  its  division  into  two  areas, 
the  one  central  and  the  other  peripheral,  both  having  distinct  attributes. 

3.  Direct  and  crossed  tracts. — This  being  allowed,  it  is  found  that, 
from  another  point  of  view,  the  retina  and  the  tracts  of  the  optic  nerve 
arising  in  it,  present  a  second  division  which  is  effected  in  the  folloAving 
maimer  :  each  of  the  retinae  of  the  right  and  left  eye  is  itself  divided 
into  a  right  and  left  portion,  mutually  unequal  (two-thirds  on  one  side 
and  one-third  on  the  other),  by  a  vertical  line  passing  through  the 
macula.  That  portion  of  the  optic  nerve  which  corresponds  to  the 
temporal  area  proceeds  to  the  cerebral  hemisphere  of  the  same  side  ; 
that  corresponding  to  the  nasal  area  decussates  in  the  chiasma  with 
its  homologue  in  order  to  reach  the  hemisphere  of  the  opposite  side. 
This  decussation  affects  the  macular  tract  as  all  the  rest.  As  regards 
each  eye,  the  term  nasal  is  applied  to  the  inner  area  (with  reference  to 
the  median  line  of  the  body)  and  temporal  to  the  external  area  ;  the 
nasal  area  is  the  most  extensive  of  the  two. 

4.  Corresponding  areas  ;  identical  points  of  the  retina. — Though  the 
nasal  and  temporal  areas  correspond  with  each  other  from  the  point 
of  view  of  ordinary  symmetry,  the  same  cannot  be  said  A\dth  regard 
to  the  normal  exercise  of  vision  with  both  eyes.  An  object  placed  to 
the  right  throws  its  image  on  the  two  left  areas  of  each  r-etina,  an  object 
placed  to  the  left  on  the  two  right  areas.  Thus  each  point  of  the  object 
throws  two  images,  one  on  each  right  or  left  area  of  the  two  retinae. 
These  points,  which  are  called  corresponding  or  identical  (J.  Miiller), 
are  mutually  united  by  the  nervous  system  in  such  a  way  as  to  cause 
these  two  images  to  be  fused  into  one  in  the  sensorium.  These  points 
being  once  fixed,  it  is  necessary  for  the  exercise  of  normal  vision  that 
they  should  continue  in  the  same  mutual  relations  as  regards  distance 
during  every  movement  of  the  eyes. 

5.  Homonymous  hemianopsia. — Should  the  optic  nerve  on  one  side 
be  interrupted,  loss  of  vision  in  the  corresponding  eye  would  naturally 


VISUAL    INNERVATION  563 

ensue.  If  the  optic  tract  of  this  same  side  is  interrupted,  there  is  loss 
of  vision  in  each  of  the  corresponding  half  retinae,  the  temporal  on 
the  same  side  and  the  nasal  on  the  opposite  side.  This  is  called 
homonymous  hemianopsia,  because  the  two  half  retinae  deprived  of 
sight  are  those  of  the  side  corresponding  to  the  lesion.  In  other  words, 
the  two  temporal  areas  give  off  direct  fibres  (connected  mth  the  hemi- 
sphere of  the  same  side),  the  two  nasal  areas  give  rise  to  decussated 
fibres  (in  relation  to  the  opposite  hemisphere)  ;  or,  to  put  it  otherwise, 
the  two  right  areas  of  each  retina  are  connected  with  the  right  hemi- 
sphere, the  two  left  areas  with  the  left  hemisphere.  Grasset  remarks 
on  this  subject  that  the  optic  nerve  only  exists  as  a  physiological  unit 
in  the  optic  tract,  and  that  in  strictness  it  should  be  described  as  the 
hemioidic  nerve. 

Remark. — If  a  hemisphere  is  injured  or  the  optic  tract  interrupted,  it  is  the 
half  retinae  of  the  same  side  which  are  paralysed,  but  the  objects  on  the  opposite 
side  are  those  which  are  no  longer  seen.  This  is  explained  very  easily  by  the 
fact  that  the  images  of  these  objects  are  reversed  on  the  retina  on  accovmt  of 
the  passage  of  the  rays  through  the  media  of  the  eye.  This  disappearance  of 
sight  to  the  right  or  the  left  in  the  case  of  experimental  or  pathological  lesions 
of  one  or  the  other  hemispliere  has  given  rise  to  the  belief  which  for  some  time 
prevailed  that  the  sight  of  the  right  or  the  left  eye  was  paralysed  in  an  isolated 
manner,  and  as  a  finishing  touch  to  this  error,  that  the  paralysis  affected  the 
ej^e  opposite  to  the  lesion.  By  closiag  each  of  the  eyes  separately,  it  is  easily 
seen  that  the  sight  in  each  is  partially  preserved  and  partially  extinguished, 
according  to  the  above-mentioned  division. 

Decussation  of  fibres  in  the  chiasma. — Since  the  time  of  Newton,  who  first 
considered  the  question,  the  decussation,  whether  partial  or  complete,  of  the 
optic  nerve  has  been  continually  discussed.  In  inferior  vertebrata  we  find  the 
eyes  placed  laterally  and  tlie  vision  monocular ;  in  them  the  decussation  is 
complete.  Even  in  mammals,  examples  of  total  decussation  may  be  fovuid: 
for  instance,  in  the  guinea  pig  and  the  mouse  ;  it  is  partial  in  the  rabbit,  the 
dog  and  the  cat  ;  in  the  primates  it  is  much  the  same  as  in  man.  In  the  last 
named  the  proportion  of  fibres  would  be  150,000  direct  to  250,000  crossed 
(Ivrause,  Salzer). 

Experiment. — -Nicati,  after  having  cut  the  chiasma  of  the  optic  nerves  in  the 
median  line,  across  the  bones  of  the  base  of  the  skull,  in  a  young  cat,  observed 
that  vision  partially  persisted  in  the  two  ej'es,  this  proving  that  a  certain  portion 
of  the  fibres  escape  decussation. 

Amblyopia  by  sensory  anaesthesia. — The  isolated  lesion  of  a  hemisphere  never 
produces  crossed  amblyoj^ia  or  hemiopia ;  but  constantly  causes  bilateral 
homonjinovxs  hemianopsia.  Unilateral  amblyopia  or  hemiopia  may  be  observed 
as  a  natural  consequence  of  the  interruption  of  the  optic  nerve,  but  it  may  also 
have  a  more  complex  origin.  Clinically,  an  amblyopia  of  this  nature  generally 
arises  in  connexion  with  an  anaesthesia  of  the  ball  of  the  eye.  It  may  be 
observed  in  hysteria,  when  it  occasionally  causes  a  very  marked  contraction  of 
the  field  of  vision,  and  it  only  occm-s  when  there  are  contemporaneous  dis- 
tm'bances  of  general  sensation  which  affect  the  ball  of  the  eye,  and  it  is  more 
marked  in  proportion  to  the  strength  of  these  disturbances  (Ferre).  It  may 
be  reproduced  experimentally  by  inducing  lesions  of  the  nervous  system  en- 


564 


SPECIAL    INNERVATIONS 


tailing  anaesthesia,  whether  these  lesions  have  a  central  cortical  origin  (Lanne- 
grace),  or  whether  they  are,  on  the  contrary,  peripheral,  or  equivalent  to  peri- 
pheral lesions  (Bechterew).  It  may,  in  fact,  be  induced  by  section  of  the  tri- 
geminal, especially  of  its  ascending  root.  The  sensory  anaesthesia  which  ensues 
in  the  corresponding  half  of  the  face  is  accompanied  by  a  diminution  in  the 
acuteness  of  the  senses  (hearing,  smell,  taste),  as  has  been  pointed  out  by  those 
who  have  experimented  on  section  of  this  nerve. 

Thus  the  sensorial  distm-bances  following  the  paralysis  of  this  nerve  are  of  a 

secondary     nature. 
//  \f.  „/tt;        Section  of  the  trigemi- 

nal nerve  interrupts 
not  only  sensory  fibres, 
but  also  vaso-motor 
elements,  and  pro- 
bably also  elements 
whose  function  is  of  a 
more  indeterminate 
natm"e,  and  whose  in- 
terruption is  rendered 
evident  b  y  trophic 
disturbances.  In  all 
cases  the  section  is 
followed  by  disturb- 
a  n  c  e  s  of  nutrition, 
w  h  i  c  h  explain  the 
diminution  or  lack  of 
function  of  the  sensory 
organs  situated  in  its 
area  of  distribution. 

6,  Persistence  of 
the  retinal  impres- 
sions.— The  imjjres- 
sion  made  on  the 
retina  by  a  lumin- 
ous excitant  persists  for  a  certain  time  after  its  cessation.  The 
most  simple  illustration  of  this  is  afforded  by  a  red-hot  coal  which,  if 
moved  in  a  circular  direction,  gives  the  impression  of  an  incandescent 
circle.  The  cinematograph  is  founded  on  this  fact.  This  persistence 
varies  according  to  the  intensity  of  the  light  emitted  by  the  object 
which  stimulates  the  retina.  Helmholtz  has  observed  it  to  vary 
from  -Lt^  of  a  second  in  the  case  of  very  brilliant  to  yV  o^  ^  second  in 
that  of  feeble  illuminations  ;  -r>j^  of  a  second  would  be  a  maximum 
figure,  impossible  to  go  beyond,  and,  indeed,  hardly  to  be  attained 
even  with  the  strongest  illuminations  (Parinaud). 


I IG.  231. — Diagram  of  the  structvire  of  the  optic  nerve  (after 
Van  Gehuchten). 


Consecutive  images. — When  the  more  or  less  persistent  j^rimary  image  has 
ceased  and  the  eye  is  suddenly  plunged  into  darkness,  a  consecutive  image, 
which  has  been  named  positive,  makes  its  appearance  after  a  short  time  ;  this 
name  has  been  given  it  because  it  reproduces  the  first  image  without  inverting 


VISUAL    INNERVATION  565 

its  tones  (white  for  white,  black  for  black).  This  image  is  progressively  effaced, 
and  after  a  time,  which  may  vary  from  a  second  to  a  minute  or  longer,  it  is 
usually  replaced  by  a  negative  image,  in  which  the  tones  are  reversed  (black  for 
white,  or  the  colour  which  is  generally  complementary  instead  of  the  primary 
coloiu').  The  negative  image  may  not  appear  when  the  first  impression  has 
been  a  feeble  one. 

Retinal  oscillations  and  interferences. — Thus  a  luminous  stimulation  has  both 
immediate  and  consecutive  effects.  When  studied  in  detail,  both  will  be  found 
to  be  complicated.  The  immediate  impression  is  itself  an  effect  of  an  oscillatory 
nature.  A.  Charpentier  maintains  that  all  luminous  stimulation  (whatever  be 
its  colour  and  intensity)  gives  rise  to  a  negative  undulation  in  the  retina,  probably 
followed  by  other  oscillations  analogous  to  it,  but  which  are  less  easy  to  observe. 

(«)  Oscillation  arises  in  a  stimulated  point  ^/^  to  ^'^  of  a  second  after  the  com- 
mencement of  the  stimulation  ;  the  period  of  complete  oscillation  being  from  .,/jy 
to  tJ-  of  a  second,  (b)  This  oscillation,  starting  from  the  excited  point,  extends 
gradually  on  the  retina  at  the  rate  of  72  millirnetres  the  second. 

Experiment. — A  black  disc  carries  a  white  well-lighted  sector,  and  is  caused 
to  rotate  on  its  axis  at  the  rate  of  one  turn  in  two  seconds.  The  eyes  must  be 
immovably  fixed  exactly  on  the  centre  of  the  disc.  A  black  sector,  with  a 
softened  outline,  is  seen  to  appear,  covering  a  portion  of  the  white  sector.  If 
the  rate  of  rotation  be  increased,  this  black  band  becomes  larger  ;  should  the 
rate  be  diminished,  it  decreases  in  size.  By  calculating  the  rate  of  rotation 
and  the  distance  separating  the  black  band  from  the  border  of  the  white  sector 
the  interval  which  has  elapsed  between  the  appearance  of  the  white  edge  and 
that  of  the  black  edge  arising  on  it  may  be  deduced.  This  interval  is  ^^^  to  J^ 
of  a  second. 

Charpentier  maintains  that  the  negative  wave  answering  to  this  black  band 
travels  successively  over  the  different  meridians  of  the  retina.  It  always  arrives 
■gJ^  to  7^0  of  a  second  after  this  point  has  been  touched  by  the  beginning  of  the 
white  sector. 

The  starting  of  the  stimulation  produces  an  oscillation  at  the  point  stimu- 
lated. The  duration  of  the  complete  oscillation  being  from  ^^  to  ^.^  of  a  second, 
after  from  -^jj  to  Jy^  of  a  second  the  oscillatory  phase  is  negative. 

The  fresh  excitation  (of  a  positive  order)  is  superposed  to  it  ;  hence  arises 
interference,  opposition  of  contrary  movements,  and  thus  darkness  ensues  : 
+  A    +  (   -  A)  =0. 

The  study  of  the  excitability  of  the  retina  will  be  resinned  in  detail  with 
regard  to  the  functions  of  the  organs  of  the  senses.  What  we  have  stated  above 
merely  indicates  that,  starting  from  the  retina,  the  phenomenon  of  visual  stimu- 
lation is  one  of  great  complexity,  and  cannot  be  explained  by  a  simple  trans- 
mission of  a  nervous  impulse  through  isolated  fibres.  From  the  retina  there 
is  a  tendency  to  the  diffusion  of  the  impulse  in  an  area  near  to  the  point  directly 
stimulated.  The  distinctness  of  the  psychical  image  is  no  longer,  like  that 
of  the  physcial  image,  determined  by  the  existence  of  a  geometrical  arrangement 
which  continues  across  the  optic  paths  up  to  the  cerebral  cortex. 

■  7.  Unity  of  sensation  in  binocular  vision. — In  binocular  vision  the 
two  physical  images  formed  at  the  back  of  each  eye  are  fused,  into  a 
single  psychical  image.  This  synthetic  phenomenon  is  in  reality  not 
more  surprising  than  are  many  others  from  which  our  sensations  and 
perceptions  result  ;  but  it  is  here  more  obvious,  and  strikes  us  more 
forcibly  on  account  of  the  distinct  separation  between  the  elements 


566  SPECIAL    INNERVATIONS 

by  which  the  sensation  is  perfected.  An  attempt  has  been  made  to 
explain  this  by  observing  that  the  impressions  received  on  the  homony- 
mous areas,  that  is  to  say,  the  right  and  left  halves  of  the  two  retinae, 
converge  by  means  of  the  optic  tracts  and  the  optic  radiations  towards 
the  same  cerebral  hemisphere,  in  which  are  thus  superposed  nervous 
waves  of  the  same  form  and  the  same  succession.  But  this  is  only  a 
part  of  the  explanation  ;  it  remains  to  be  shown  how  these  psychical 
images  formed  in  the  two  hemispheres  are,  in  their  turn,  superposed 
so  as  to  form  a  single  image.  To  effect  this  the  inter-hemispherical 
commissures  must  take  part,  the  most  important  of  them  being  the 
corpus  callosum,  which  sohdarize  the  functions  of  the  two  halves  of 
the  brain.  We  relapse  into  the  formula  common  to  all  sensation  ;  a 
phenomenon  which  in  itseK  and  by  definition  ensures  unity,  but  whose 
physiological  analysis  displays  component  elements,  proving  them  to 
be  the  more  dissociated  the  farther  they  are  removed  from  the  cerebral 
cortex. 

Fiirther,  it  must  be  remarked  that  the  right  and  left  areas  of  the  two  retinae 
are  not  those  which  play  the  most  important  part  in  vision,  but  rather  the 
central  area,  or  that  of  the  yellow  spot,  placed  on  the  line  of  division  between 
the  preceding.  It  seems  often  to  be  maintained  that  the  yellow  spot  is  itself 
divided  by  hemianopsia  into  two  halves,  one  being  insensitive  and  the  other 
sensitive.  According  to  Monakow,  disturbances  localized  in  one  hemisphere 
would,  on  the  contrary,  respect  the  macula  lutea  in  great  measure,  while  they 
would  suppress  vision  in  the  homonymous  areas  of  the  periphery.  An  attempt 
has  been  made  to  explain  this  fact  by  assmning  that  the  macula  of  each  side  is 
united  to  the  two  hemispheres  at  the  same  time,  or  else  by  maintaining  the  evi- 
dence of  a  cortical  localization  of  the  impulses  from  the  macula  which  would  be 
different  from  that  of  the  rest  of  the  retina.  Monakow,  on  the  contrary,  thinks 
that  its  cortical  territory  is  much  more  diffuse,  and  that  herein  lies  the  reason 
of  its  comparative  escape  from  paralysis. 

However  this  may  be,  the  image  of  an  object  placed  directly  before  the  eye 
and  formed  in  the  centre  of  the  macula  is,  as  it  were,  astride  fibres  wliich,  being 
partially  crossed  like  the  others,  project  it  on  the  two  hemispheres,  the  synthesis 
of  the  object  being  still  made  in  the  sensorium. 

C.     CEREBRAL  VISUAL  SPHERE 

One  portion  of  the  area  of  the  cerebral  cortex  is  devoted  to  vision. 
The  visual  sphere,  as  Munek  calls  it  (and  this  designation  is  incon- 
testably  more  correct  than  that  of  centre),  is  situated  on  the  surface  of 
the  occipital  lobe. 

1 .  Former  experiments  and  observations. — Gratiolet  in  1 854  discovered 
the  optic  radiations  and  followed  them  from  the  basal  gangha,  and 
especially  from  the  external  geniculate  body  of  which  he  perceived 
the  great  importance,  up  to  the  cortex  of  the  occipital  and  parietal 
lobes.  Panizza,  in  1855,  observed  the  unilateral  and  crossed  blindness 
which  follows  the  removal  of  the  posterior  convolutions  of  the  brain 


VISUAL    INNERVATION 


567 


Len   nud      Int  cap. 


or  lesions  of  the  white  fibres  uniting  them  with  the  basal  ganglia  ;  when 
the  lesion  is  bilateral,  the  blindness  is  complete,  but  the  other  functions 
are  preserved.  He  also  noticed  the  ascending  degeneration  of  these 
tracts,  and  of  their  ganglia  of  origin,  in  the  case  of  loss  or  removal  of 
the  eye.  The  error  which  led  him  to  believe  in  unilateral  blindness, 
implying  a  complete  crossing  of  the  optic  nerves,  was  generally  diffused, 
and  was  only  rectified  much  later,  and  after  much  discussion.  It  is 
also  explained  by  the  usually  preponderating  importance,  especially 
in  animals,  of  the  crossed  tract  over  the  other,  and  also  by  the  direction 
which  it  is  necessary  to  give  to  objects  in  order  that  their  image  may 
be  thrown  on  the  retina.  The  objects  placed  on  our  right  are  seen  by 
the  left  halves  of  the  two  re- 
tinae, and  conversely  for  those 
situated  on  our  left. 

2.  Cuneus  and  calcarine 
fissure. — Physiology  and  clini- 
cal experience  are  quite  agreed 
with  regard  to  the  localization 
of  the  visual  sphere  of  the  cor- 
tex on  the  internal  surface  of 
the  occipital  lobe,  in  an  area 
chiefly  comprehending  the  cal- 
carine fissure.  Some  authors 
have  considered  this  area  to  be 
limited  to  the  lips  of  this  fissure 
only  (Henschen),  others  (Mona- 
kow)  that  it  extends  as  far  as 
the  three  convolutions  of  the 
external  surface  of  the  occipital 
lobe,  and  that  it  even  en- 
croaches on  the  posterior  por- 
tion of  the  parietal  lobe.     Most, 


11  iben 


-  Puhinar 


Occip.  corn. 


Fig.   232. 


-Optic^radiations 
lobe. 


tic.  sulcus 


..  Inf.  I.  Tract 


and     occipital 


Horizontal  section  of  the  left  hemisjjhere  (after 
Cliarpy). 


however,  regard  it  as  being  restricted  to  the  internal  surface  of  this  lobe 
(Bouveret)  ;  it  essentially  includes  the  cuneus  and  a  portion  of  the 
lingual  lobe,  that  is  to  say,  the  two  convolutions  forming  the  boundaries 
of  the  calcarine  fissure  (Dejerine.  Vialet,  Brissaud). 


In  animals  the  cortical  visvial  sphere  has,  by  the  experiments  of  Mmick,  been 
lacated  in  the  occipital  lobe. 

Vitzon  Ims  observed  unilateral  ablation,  total  and  simultaneous,  of  the 
l>osterior  tliird  of  the  first,  second  and  third  parallel  convolutions  of  the 
occipital  lobe,  to  be  followed,  in  the  dog,  by  bilateral  homonymous  hemianopsia. 
Blindness    affected   three  quarters  of   the   retina  of  the  opposite   side,   and   a 


568  SPECIAL    INNERVATIONS 

quarter  of  the  retina  of  the  same  side.    The  decussation  of   the  optic  fibres  in 
this  animal  was  therefore  effected  in  the  proportion  of  three  fourths  to  a  fourth. 

Lesions  of  the  angular  gyrus. — Experimenters  and  observers  have, 
nevertheless,  pointed  out  the  pli  courbe  or  gyrus  angularis,  situated 
on  the  external  surface  of  the  brain,  as  being  the  cortical  centre  of 
vision.  Their  error  is  explained  by  the  anatomical  fact  that  the  optic 
radiations,  in  their  journey  from  the  basal  ganglia  to  the  occipital 
lobe,  pass  slightly  below  the  cortex  of  the  angular  gyrus  and  are  easily 
cut  or  compressed  by  changes  affecting  the  latter. 

Stripe  of  Vicq  d'Azyr. — {Ruban  de  Vicq  d'Azyr.)  Differences  in  form,  struc- 
ture and  arrangement  of  elements  lead  us  to  suspect  differences  of  function, 
and  this  even  when  the  mechanism  of  these  functions  is  unknown  to  us.  It 
has  been  noticed  that  the  structure  of  the  cortex  of  the  calcarine  fissure  slightly 
differs  from  that  of  the  neighbouring  cortex  of  the  occipital  lobe  ;  the  difference 
consists  in  the  greater  thickness  of  the  molecu^lar  layer,  and  also  in  the  develop- 
ment of  a  band  of  horizontal  fibres,  the  stripe  of  Vicq  d'Azyr  (ruban  de 
Vicq  d'Azyr). 

3.  Surface  of  projection. — Several  authors  call  the  visual  sphere  a 
"  cortical  retina,"  intending  by  this  appellation  to  point  out  that  each 
point  of  the  retina  is  united  to  the  cortex  by  conducting  fibres,  whose 
terminations  in  it  repeat  on  its  surface  relations  analogous  to  those 
which  they  mutually  possess  in  the  ocular  retina.  But  they  cease  to 
be  in  agreement  when  the  question  of  defining  these  relations  arises  ; 
and  it  must  be  admitted  that  facts  are  wanting,  both  as  regards  number 
and  value,  not  merely  as  concerns  the  arrangement  in  detail,  but  also 
to  guarantee  the  principle. 

Geometrical  projection  on  the  cortex. — Thus,  for  exanaple,  in  a  case  of  atrophy 
of  tlie  superior  lip  of  the  calcarine  fissvire,  the  occurrence  of  a  hemianopsia, 
limited  to  tlie  lower  quarter  of  the  visual  field  on  both  sides,  has  been  recorded 
(Hun).  In  a  similar  case,  but  one  in  which  the  lesion  occurred  on  the  inferior 
lip  of  the  same  fissure,  a  hemianopsia  of  the  upper  quarter  of  the  visual  field 
has  been  noticed  ( Wilbrand).  Yet  the  localizations  of  the  macular  and  marginal 
l^ortions  would  not  possess  the  concentric  arrangement  which  they  have  at  the 
back  of  the  eye,  but  the  first  would  be  at  the  anterior  and  the  second  at  the 
posterior  portion  of  the  calcarine  fissure. 

Objections. — We  must  repeat  that  these  localizations  require  confirmation. 
Monakow  has  challenged  the  jDrineii^le,  supporting  his  objections  by  numerous 
facts  showing  the  physiological  importance  of  the  intermediate  ganglion  (the 
external  geniculate  body),  which  interrupts  the  continuity  of  the  conducting: 
elements,  so  that  they  cease  to  be  visible  in  the  shape  of  unbroken  fibres,  whose 
extremities  would  be  spread  out  over  two  opposed  surfaces  :  that  is  to  say, 
the  retina  and  the  occipital  cortex.  The  grey  matter,  wherever  existing — and 
this  we  know  from  a  hundred  examples — creates  associations,  and  therefore  new 
relations,  between  tlie  conducting  paths  arriving  in  it  and  those  whicli  leave  it. 
An  aceiu-ate  projection  of  the  retina  on  the  cortex  is  not  only  not  demonstrated, 
it  is  also  improbable. 

Composite  projection. — That  which  is  called  projection  on  the  cortex  is,  in 


VISUAL    INNERVATION  569 

fact,  a  perfectly  ordered,  but  extremely  conijslex,  shock,  affecting  the  cyclic 
visual  system  both  in  breadth  and  in  depth  according  to  laws  of  which  we  are 
ignorant.  One  necessary  condition  is  evident,  namely,  that,  for  similar  images, 
this  shock  must  be  regulated  in  a  similar  manner  and  for  different  images  in  a 
differing  manner.  But  the  simple  conditions  as  regards  the  formation  of  the 
retinal  image  are  no  longer  those  which  preside  over  the  formation  of  the  cerebral 
image,  itself  giving  rise  to  the  psychical  image.  When  the  retinal  image  changes 
its  place  on  the  retina,  it  is  indeed  probable  that  the  cerebral  iinage  also  changes 
its  place  in  the  cortical  sensorial  field  ;  but  this  phenomena  of  the  localization 
of  the  cerebral  image  is  distinct  from  that  presiding  over  its  production. 

Limits  of  the  visual  sphere. — Nothing  is  more  undecided  or  more 
difficult  to  deline  than  the  limits  of  the  cortical  area  which  appertains 
to  vision,  though  in  point  of  fact  the  same  may  be  said  with  regard  to 
all  the  other  senses  ;  and  nothing  is  more  deceptive  than  any  attempt 
to  trace  these  limits  in  a  hard-and-fast  manner.  In  fact,  if  each  of  the 
senses  is  rigorously  localized  at  the  periphery  of  the  body  in  special 
apparatus  only  adapted  to  distinct  varieties  of  shock,  it  is  not  so  in 
the  brain,  and  especially  not  so  in  the  cortex,  whose  function  it  is,  not 
merely  to  collect  these  impulses,  but  to  put  them  in  conflict  with  each 
other,  so  as  to  extract  the  elements  of  knowledge  from  them,  and  finally 
to  send  them  forth  under  the  form  of  motor  activity. 

Discordant  evidence. — Distinct  vision  has  sometimes  been  preserved  in  an 
extremely  small  visual  field  (for  example,  an  extent  of  from  only  3  to  5  degrees 
around  the  point  of  fixation),  which  still  allowed  the  patient  sufficient  visual 
acuity  to  read  or  to  occupy  himself  with  different  kinds  of  work  :  the  occipital 
lobe  showed  very  extensive  areas  of  softening,  with  preservation  of  certain  very 
limited  portions  of  the  cortex  of'  the  calcarine  fissm-e.  But  the  observers  by 
whom  the  facts  were  confirmed  disagreed  concerning  the  localization  of  this 
portion  of  the  grey  matter:  according  to  Hensclien,  it  is  in  the  anterior  portion 
of  the  fissure,  but  according  to  Forster  and  Sachs  in  the  posterior  portion. 
Henschen  thinks  that  there  is  a  surface  dissociation  of  the  centres  corresponding 
to  the  yellow  spot  and  to  the  margin  of  the  retina  ;  but  Munck  is  of  opinion 
that  there  is  exact  projection  of  the  ociilar  retina  on  the  cortex,  and  therefore 
a  concentric  arrangement  of  the  two  centres. 

4.  Luminous  sensation  and  mental  vision. — Before  endeavouring  to 
delimit  the  anatomical  area  of  the  visual  sphere,  it  will  first  be 
necessary  to  define  what  is  exactly  implied  by  vision.  From  crude 
sensation  of  light  or  of  colour  up  to  mental  vision  a  graduated  field  of 
phenomena  exists,  each  effected  by  functional  nervous  associations 
which  are  definite  in  their  determinism,  but  variable  according  to  each 
modality  of  the  phenomenon.  These  are  the  gradations  which  more 
or  less  extensive  destructions  of  the  cortex  may  sometimes  bring  into 
notice,  unless  they  are  of  too  delicate  a  nature  to  be  grasped. 

Cortical  retina. — The  expression  cortical  retina  has  practically  merely  a  meta- 
phorical signification.     As  opposed  to  the  locality  where  the  impression  of  light 


570 


SPECIAL    INNERVATIONS 


which  is  at  fii'st  pvirely  physical,  has  been  received,  it  implies  another  locality, 
where  this  impression,  after  successive  transformations,  has  given  rise  to  the 
psychical  phenomenon  of  sensation.  If  this  expression  be  retained,  it  must  in 
no  case  be  considered  as  being  the  equivalent  of  "  visual  sphere  "  :  the  cortical 
retina  would  imply  the  field  of  visual  sensation,  while  the  visual  sphere  would 
correspond  to  the  field  of  mental  vision,  botli  of  them  possessing  undefined 
and  indeterminate  limits. 

5.  Different  forms  of  blindness. — It  is  possible  to  be  blind  to  white 
light  and  to  colours  at  the  same  time  ;  and  it  is  also  possible  to  be  bHnd 
to  colours  only.  This  limited  blindness  may  appertain  to  all  colours 
{achroinatojma),  or  only  to  some  special  ones  {dyschromatopsia).  In 
the  case  of  unilateral  cerebral  lesion,  there  wiU  be  hemiachromatopsia, 
or  hemidyschromatopsia. 

Conditions  of  their  production. —  On  the  surface  of  the  retina  (at  the  starting 
point  of  the  impulse),  the  chromatic  function  is  localized  in  special  elements 
(the  cones)  different  from  those  which  are  sensitive  to  light  without  distinction 
of  colour  (the  rods).     In  the  retina,  colour  vision  is  central  and  vision  apart 


Vcriicul  Truci 


Trins.  Tract  uf 
t/.e  ciineus 


C  uncus 


Calc.  fi^i 


Strut,  culc 


Tapetum 


0'^  ling. 


yL.J^ 


Fib.  arcuute 


Trans.  Hnj. 
Trad 


Fig.  233. — The  tracts  of  association  of  the  occipital  lobe. 
Diagrammatic  transverse  section. — Left  hemisphere  (after  Dejerine). 

from  colovir  is  marginal.  Is  it  the  same  in  the  cerebral  cortex  ?  Nothing  in- 
dicates this  in  a  definite  manner,  and  probability  is  not  in  favour  of  such  a 
symmetry.  On  the  other  hand,  to  mark  out  a  cellular  layer  devoted  to  the 
colour  sense  in  the  cortex  of  the  grey  occipital  matter,  is  to  bring  forward  an 


VISUAL    INNERVATION  571 

absolutel}'  gratuitous  and  unverifiable  hypothesis,  since  there  is  no  chance  of 
finding  or  artificially  producing  a  lesion  affecting  preferably  one  cellular  layer 
to  the  exclusion  of  others.  With  regard  to  surface  localization,  so  much  is  still 
wanting  that  clinical  observations  followed  by  autopsy  do  not  authorize  our 
acceptance  of  it. 

Some  prefer  to  maintain  that  coloiu"  vision  is  not  distinctly  localized  apart 
from  that  of  light,  but  that  it  merely  depends  on  certain  special  conditions, 
such  as  a  very  perfect  preservation  of  the  u'ritabUity  of  the  elements  and  an 
adequate  blood  supply  ;  or,  again,  on  a  more  extended  visual  field.  In  the 
case  mentioned  by  Forster,  in  wliich  the  visual  field  was  extremely  restricted, 
there  was  colour  blindness.  Cerebral  lesions,  according  to  their  intensity  or 
their  extent,  would  thus  cause,  in  the  first  place,  loss  of  the  sense  of  colom" 
(the  most  fugitive);  then  that  of  the  sense  of  light;  lastly,  complete  blind- 
ness. Green  and  red  are  the  first  to  be  lost;  then  .blue;  and  finally,  the  con- 
ception of  black  and  white  (Holden).  In  general  the  appreciation  of  various 
intensities  of  light  continues  to  decrease  with  that  of  colovus,  though  in  the 
end  stu'viving  it  :  but  clinical  observation,  which  teaches  us  so  much,  brings 
forward  a  case  where  loss  of  colour  vision  occiu-red  without  diminution  of  sensi- 
bility to  light  (Stefan),  and  this  case  is  quoted  as  an  argument  by  those  who 
maintain  the  independent  existence  of  a  centre  for  chromatic  vision  ;  but  there 
is  nothing  convincing  about  it. 

8.  Conceptions  of  form,  space,  locality  and  of  orientation, — To  the 
simple  conception  of  light,  and  to  that  more  complicated  idea  of  colours, 
are  added,  in  the  exercise  of  vision,  other  notions  which  are  generally 
so  strictly  associated  with  each  other  that  they  are  only  distinguishable 
by  analysis  ;  these  are  the  ideas  concerning  the  form  of  objects,  and 
the  mutual  relations  of  these  objects,  as  well  as  those  with  ourselves. 
These  ideas  are  far  more  complicated  than  the  preceding  ones.  By 
the  combination  of  light  and  shadow  as  well  as  colours,  images  are 
formed  on  the  retina.  These  images  are  brought  into  being  by  associa- 
tion in  a  given  order,  that  is  to  say,  by  the  synthesis  of  these  elements 
(luminous  and  chromatic  phenomena).  This  synthesis  is  a  psychical 
fact.  Each  of  these  elements  exists  independently  ;  their  association 
in  our  consciousness  is  what  gives  the  image  its  reality. 

7.  Physical  image  and  psychical  image. — Physics  teaches  us  how 
luminous  rays  emitted  by  objects  or  reflected  bj^  them,  while  preserving 
their  respective  relations,  may,  when  falling  on  a  screen,  fui'nish  a  repre- 
sentation which  exactly  recalls  these  objects,  and  which  is  of  about  the 
same  dimensions.  This  is  what  is  known  as  the  physical  image  of  these 
objects.  It  is  by  an  image  of  this  nature  that  objects  make  an  im- 
pression on  the  retina,  and  this  image  is  as  much  a  physical  one  as 
that  which  was  thrown  on  the  screen.  But  the  retina  possesses,  as 
the  scr.een  does  not,  nervous  paths  which  carry  this  impression  into 
the  depths  of  a  system  whose  strictly  consohdated  parts  form  a  really 
united  being,  and  this  unity  is  revealed  in  it  by  that  which  we  call 
■consciousness.     In  this  case  the  physical  image  is  duphcated  by  a 


572  SPECIAL    INNERVATIONS 

psychical  image,  or,  to  put  it  better,  the  consciousness,  by  arranging 
the  characteristics  of  the  physical  image,  and  at  the  same  time  detach- 
ing it  from  all  surrounding  phenomena,  confers  upon  it  its  unity,  that 
is  to  say,  its  existence.  This  is  not  the  ajDpropriate  place  for  explaining 
the  manner  in  which,  from  the  retinal  image,  we  ascend  to  the  objects. 

8.  Empty  space  and  occupied  space. — Whatever  the  reason  may  be, 
it  seems  that  even  from  the  fact  of  their  original  complexity,  these 
conceptions  of  form  are  more  easily  alterable  than  the  elementary 
sensations  which  gave  rise  to  them.  It  has  been  observed  that,  in 
double  lesions  of  the  occipital  lobe,  individuals  injured  in  this  way  lose 
the  faculty  of  recognizing  locaUties  which  should  be  familiar  to  them. 
The  general  idea  of  space  may  be  preserved,  but  that  of  space  furnished 
with  objects  no  longer  exists  with  its  characteristic  attributes  for  these 
patients  :    they  have  lost  the  memory  of  localities. 

An  endeavour  has  been  made  to  find  in  the  occipital  cortex,  both  in 
its  depth  and  on  its  surface,  a  special  centre  of  visual  acuity  and  of 
vision  in  space  ;  but  here  again,  facts  are  wanting  which  would  serve 
as  a  basis  for  such  a  conception,  which  no  satisfactory  theoretical  reason 
suggests  to  us.  What  appears  to  be  certain  is,  that  the  cerebral  field 
whose  activity  'presides  over  recognition  of  forms  and  jdaces  is  more  ex- 
tensive than  that  for  the  crude  sensation  of  light ;  the  nervous  apparatus 
of  the  one  differs  from  that  of  the  other,  just  as  the  first  of  these  pheno- 
mena differs  from  the  second,  or  just  as  the  composite  differs  from  the 
simple. 

Exteriorization  of  sensation.^Objects  are  situated  externally  to  us,  and  we 
have  a  knowledge  of  tlieir  existence  :  it  must  therefore  be  that  something  comes 
from  them  to  us,  carrying  with  it  the  elements  of  tliis  knowledge.  The  aerial 
medium  and  especially  the  ether  (this  last  penetrating  all  the  others  without 
being  confounded  with  them),  carries  out  this  transmission  as  regards  objects 
at  a  distance.  Something  which  has,  as  it  were,  taken  the  impress  of  these 
objects  thus  comes  to  us  and  reconstitutes  this  impress  on  the  sensory  surface 
of  our  body  ;    this  is  very  evident  with  regard  to  the  sense  of  sight. 

This  impression,  however,  has  not  finished  its  progress  by  its  arrival  at  the 
retina  ;  it  travels  thence  by  quite  new  and  special  paths  (the  nervous  paths), 
in  order  to  reach  the  cerebral  cortex  ;  there  alone  does  this  imprint  or  this 
impression  become  sensation,  perce]:)tion,  or  knowledge.  This  amounts  to  say- 
ing that  the  imprint,  the  image,  exists  in  us,  but  the  medium  containing  it  (and 
this  medium  is  ourselves)  is  conscious  of  so  doing.  The  external  medium  which 
transmitted  it  to  us  (it,  or  its  component  elements)  also  contained  it,  but  with- 
out the  consciousness  of  doing  so.  These  facts  are  individually  clear,  and  arise 
from  common  sense  and  from  intuition.  One  of  them,  it  is  trvie,  namely,  con- 
sciousness, eludes  all  rational  and  scientific  explanation,  and  will  probably 
always  so  elude  it,  on  account  of  our  special  situation  with  regard  to  it.  How- 
ever, for  the  present  it  will  suflfice  to  authenticate  it  and  put  it  into  its  right 
class.  R*^ 

At  the  same  time,  this  is  only  half  the  explanation.  The  forward  march  of 
the  impression  (or  of  what  produces  it)  from  the  objects  to  us  explains  clearly 


VISUAL    INNERVATION  573 

how  their  image  comes  to  exist  in  ns,  but  it  does  not  explain  how  these  objects 
are  collected  externally  to  us  in  the  locality  which  they  really  occupy.  The 
fact  is  authenticated  and  connected  with  the  preceding  datum  by  saying  that 
the  sensation,  the  mental  image,  is  projected  externally  in  the  direction  and 
even  to  the  situation  of  the  object.  Tliis  is  what  is  called  exteriorization  of 
sensation. 

These  words,  exteriorization  and  projection,  are  necessary  to  complete  the  analy- 
sis of  the  process  of  formation  of  the  mental  images  of  objects.  They  express  a 
correction  which  is  in  a  way  indispensable  in  order  to  bring  the  results  of  this 
analysis  into  agreement  with  common  sense.  In  fact,  on  the  one  hand  analysis 
evidently  displays  to  us  something  which  is  substituted  for  the  object  and  which 
progresses  in  the  first  instance  from  it  to  us,  then  within  us  up  to  the  brain  :  as 
if  this  object  had  come  to  dwell  there  and  to  manifest  its  presence  by  some  of  its 
characteristics.  But,  on  the  other  hand,  common  sense  is  not  deceived,  and  locates 
these  objects  wliere  they  really  are,  outside  of  us,  that  is  to  say,  externally  to 
ourselves  :  so  that,  after  having  caused  this  something  which  represents  the 
object  to  travel  from  it  to  our  brain,  we  feel,  for  the  sake  of  logic  and  good  sense, 
the  necessity  of  requiring  it  to  perform  the  ojDposite  journey,  that  is  to  say,  from 
our  brain  back  again  to  the  object.  To  put  it  concisely,  there  would  be  ; 
(1)  projection  from  the  object  up  to  the  brain  ;  (2)  projection  from  the  brain  to 
the  object.  What  is  this  something  which  is  launched  on  both  of  these  journeys  ? 
From  the  object  to  the  brain  the  projection  is  a  reality,  and  is  itself  divided  into 
two  successive  journeys  ;  these  are,  from  the  object  to  the  retina,  liuninous  waves 
propagated  through  the  ether,  obeying  laws  which  are  fairly  well  understood  ; 
and,  from  the  retina  to  the  brain,  nervous  waves,  of  whicli  the  direction  of  the 
propagation  (if  not  the  form)  is  distinctly  defined. 

On  the  contrary,  the  projection  from  the  brain  to  the  object  is  quite  ideal  ;  it 
is  merely  an  artifice  made  use  of  for  the  pvu*pose  of  demonstration.  It  is  the 
same  thmg  as  saying  that  physical  and  physiological  analysis  of  the  mechanism 
of  vision  only  gives  us  a  portion  of  the  knowledge  necessary  in  order  to  arrive 
at  a  clear  conception  of  it.  In  any  case  there  is  no  such  thing  as  a  nervous  retro- 
grade wave  which  returns  from  the  brain  to  the  retina  by  paths  already  traversed 
by  it  on  its  journey  from  the  retina  to  the  brain.  Doubtless  it  would  be  possible 
for  the  brain  to  reflect  these  waves,  and  thus  project  them  ovitwards,  but  it  would 
be  by  paths  quite  different  from  the  first,  and  wliich  woidd  bring  back  these  waves 
to  the  organs  of  movement,  where  finally  all  nervous  impulses  terminate. 

9.  Physical  and  psychical  blindness. — Nothing  can  be  more  instruc- 
tive from  a  psychological  point  of  view  than  the  comparison  of  two 
individuals,  of  w^hom  one  has  lost  the  ocular  apparatus  (loss  or  ablation 
of  both  eyes)  and  the  other  the  cerebral  apparatus  of  vision  (patho- 
logical destruction  of  the  occipital  cortex  or  ablation  of  the  occipital 
lobes).  Experiment  and  observation,  which  so  often  leave  questions 
undecided  because  they  are  impracticable  in  conditions  which  would 
render  them  precise,  here  find  a  field  favourable  to  their  realization 
by  attacking  the  two  positions  of  the  visual  system  which  are  the  widest 
apart,  and  by  comparing  the  deficiency  which  follows,  in  the  one  case 
the  suppression  of  the  receptive  apparatus,  that  is  to  say,  the  original 
source  of  impulses  ;  and  in  the  other,  the  suppression  of  the  essential 
mechanism  for  the  transformation  and  preservation  of  these  impulses. 


574  SPECIAL    INNERVATIONS 

The  subject,  whether  it  be  man  or  animal,  which  has  lost  both  eyes, 
no  longer  receives  any  ideas  from  the  external  world  by  the  visual 
path,  but  preserves  in  the  condition  of  remembrances  a  great  number 
of  those  previously  acquired  by  this  means,  and  which  remain  in  him 
in  the  form  of  so  many  fixed  data  round  which  to  group  the  new  ideas 
which  do  not  cease  to  flow  in  upon  him  by  the  paths  of  the  other  senses 
still  remaining  intact.  The  individual,  on  the  contrary,  who  no  longer 
retains  the  occipital  lobes  has  lost  with  them  the  accumulated  store  of 
anterior  ideas  acquired  by  sight  ;  therefore  the  information  brought 
by  touch,  hearing  and  smell  will  no  longer  have  as  a  basis  the  memories 
acquired  by  the  sense  playing  the  most  essential  part  in  the  representa- 
tion of  forms  and  places  ;  owing  to  this  fact  a  very  great  mental  in- 
feriority Avill  be  observed  in  the  second  case  when  compared  with  the 
first.  Both  subjects  are  plunged  into  obscurity,  but  the  night  of  the 
first  is  a  physical  night,  not  essentially  different  from  that  resulting 
from  a  simple  deprivation  of  light,  understood  as  vibrations  of  the 
ether  in  the  physical  sense  ;  the  night  of  the  other  is  a  psychical  night, 
in  the  sense  that  the  vibrations  of  the  ether  may  indeed  affect  the 
retina,  and  by  reverberation  the  primary  visual  paths  ;  but  light  in 
the  physiological  or  psychological  sense  of  the  word  (the  meaning  is  the 
same),  is  lacking  ;  while  in  the  first  even  this  light  is  not  absolutely 
extinguished,  and  still  less  so  are  the  forms  impressed  on  the  con- 
sciousness. 

In  physical  blindness  the  other  senses,  and  especially  that  of  touch, 
soon  become  sufficiently  educated  to  allow  of  their  supplying  to  a 
certain  extent  the  absence  of  vision  ;  this  education  being  possible, 
thanks  to  the  nucleus  of  visual  memories  preserved  in  the  brain.  In 
psychical  blindness  this  education  finds  its  principal  basis  lacking, 
above  all  in  the  adult.  The  child  born  blind,  or  the  new-born  animal, 
from  which  both  eyes  have  been  removed,  would  also  be  forced  to  create 
a  tactile  and  auditory  sense  by  the  education  of  the  remaining  senses  ; 
but  their  condition  would  be  ameliorated  by  reason  of  the  greater 
plasticity  of  their  organs  still  in  course  of  development. 

10,  Verbal  blindness. — The  word  "  psychic,"  like  many  expressions 
used  in  physiology,  may  be  understood,  sometimes  in  a  general  and 
sometimes  in  a  sjoecial  sense,  and,  until  our  language  is  enriched  with 
expressions  adequate  to  describe  these  shades  of  meaning,  it  is  better 
to  define  them  by  short  descriptions.  Psychical  blindness,  when 
understood  in  the  sense  just  referred  to,  is  equivalent  to  the  loss  of  all 
psychical  phenomena  of  a  visual  order,  from  the  crude  sensation  of  light 
up  to  ideas  of  a  most  complex  nature,  in  so  far  as  these  proceed  from 
vision.     Psychical  is  thus  taken  simply  in  an  opposite  sense  to  physical. 


VISUAL    INNERVATION  575 

We  may  thus  define  the  principal  degrees  of  this  psychical  phenomenon. 
It  is  usual  also  to  distinguish  ;  (1)  a  cortical  blindness,  equivalent  to 
the  loss  of  luminous  sensations  ;  (2)  a  jysychical  blindness,  properly 
so  called,  equivalent  to  the  loss  of  commemorative  images  of  objects  ; 
(3)  a  verbal  hhndness,  implying  the  loss  of  the  power  of  reading  words, 
or,  more  generally,  any  ^\Titten  signs.  This  last  variety  is  included 
under  the  heading  of  aphasia. 

Inferior  psychism. — Visual  images  are  projected  on  the  cortex  ;  but,  before 
reaching  it,  they  j)ass  tlxrough  the  optic  thalamus  (pulvinar)  :  this  gangHon  takes 
an  active  part  in  the  elaboration  of  visual  sensation.  After  the  removal  of  the 
cortex  of  the  occipital  lobes,  blindness  ensues,  but  after  a  certain  time  this  blind- 
ness is  ameliorated  (Munck),  exactly  as  is  the  sensory  paralysis  following  the 
ablation  of  the  tactile  cortical  area.  The  animal,  in  walking,  succeeds  in  avoid- 
ing obstacles.  There  must  then  be  some  recoverj^  of  visual  sensation  with  a 
certain  degree  of  consciousness.  The  permanent  deficiency  which  follows  destruc- 
tion of  the  cortex  is  not  tlien  characterized  (at  least  in  animals)  by  absolute  loss 
of  conscious  vision,  but  by  the  impossibility  of  elaborating  complex  images. 
As  for  the  return  of  conscious  elementary  vision,  when  this  re-appears,  there  is 
nothing  which  would  compel  us  to  consider  it  as  caused  by  a  substitution  of 
neighbouring  portions  of  the  cortex  which  have  remained  intact,  rather  than  by 
a  substitution  effected  by  the  optic  thalamus. 

Images  in  space,  orientation. — A  portion  of  the  fibres  of  the  optic  nerve,  instead 
of  proceeding  to  the  cortex  and  the  optic  thalamus,  follows  the  superior  cerebellar 
peduncle  (from  before  backwards)  and  passes  to  the  cerebellum.  This  direct 
cerebellar  tract  of  retinal  or  optic  origin  is  the  equivalent  of  tlie  direct  cerebellar 
tract  of  medullary  or  tactile  origin,  as  well  as  of  the  direct  cerebellar  tract  of  vesti- 
bular origin,  these  two  latter  reaching  the  cerebellum  by  the  inferior  cerebellar 
pedvmcle.  These  tliree  tracts  cause  the  convergence  towards  the  cerebellum  of 
impulses  originating  in  three  different  senses  or  apparatus  (sight,  touch,  vesti- 
bular apparatus)  which  are  in  it  organized  into  images  of  space  with  the  aim  of 
objective  and  subjective  orientation  (Bonnier).  An  indirect  communication  is 
established  between  the  retina  and  tlie  cerebellum  by  the  intermediation  of  the 
olive,  and  the  nuclei  of  the  pons.  Tlie  retina  also  sends  fibres  to  the  oculo-motor 
nuclei,  either  by  the  corpora  quadrigemina  or  directly  ;  whence  arises  an  appara- 
tus of  ocular  adaptation  simpler  and  stiU  less  conscious  than  the  preceding 
one. 

D.     MOTOR  EFFECTS— PATHS  OF  RETURN 

Impulses  have  innumerable  paths  in  order  to  descend  from  the 
cerebral  cortex  to  the  agents  executive  of  movements  ;  but  we  shall 
here  consider  only  those  which  are  directly  necessary  or  useful  to  the 
exercise  of  the  functions  of  vision  itself,  and  which  form,  mth  the  so- 
called  centripetal  visual  paths,  a  system  whose  component  parts,  being 
mutually  connected  by  a  functional  bond  of  union,  work  in  co-opera- 
tion. It  remains  therefore  to  point  out  these  paths  and  to  analyse 
their  mode  of  action. 

We  cannot  too  often  repeat  that  all  impulses  coming  from  the  ex- 
ternal world  do  not  penetrate  the  nervous  system  to  the  same  depth  ; 
some  do  not  reach  the  cerebral  cortex,  and  others  do  not  approach  it 


576  SPECIAL    INNERVATIONS 

to  the  same  extent.  Most  of  the  halting  places  imposed  upon  the 
impulse  by  the  grey  matter  in  its  journey  (perhaps  all  of  them)  offer 
paths  of  reflexion  to  it,  which  are  utilized  or  not  according  to  circum- 
stances. To  ascertain  with  certainty  what  determines  the  variable 
progress  of  these  impulses  through  such  multiple  and  complex  paths 
is  one  of  the  most  important  problems  of  physiology,  but  it  is  also  one 
concerning  which  all  positive  information  is  wanting.  All  we  can  do 
is  to  connect  it  with  a  statement  of  a  very  general  order  which  demon- 
strates, in  the  form  of  a  classical  formula,  the  function  creating  the 
organ.  The  impulse  in  its  progress  obeys  the  same  laiv  as  selj-organiziyig 
matter.  It  goes  ivhere  it  is  ivanted.  Thus,  just  as  in  nervous  pheno- 
mena which  the  simplifying  tendencies  of  science  permit  us  to  willingly 
regard  as  a  series  of  passive  acts  obeying  an  impulse  from  without,  we 
are  led  to  invoke  a  dinamen,  not  only  original,  but  also  incessant. 

1.  Localities  for  reflexion  of  impulses. — Whatever  may  be  the  condi- 
tions determining  its  course,  the  impulse  is  reflected,  sometimes  by 
the  cortex  and  sometimes  by  the  grey  masses  of  the  basal  ganglia. 
The  retina,  the  first  locality  reached  by  the  nervous  wave  which  arises 
at  its  surface,  may  perhaps  present  reflex  microscopic  arcs,  whose 
smallness  alone  would  prevent  their  submission  to  experimental  in- 
vestigation. This  organ  thus  removed,  there  remain  several  others 
for  us  to  examine  from  the  same  point  of  view.  Like  the  sensory 
paths,  the  motor  paths  are  complex  and  divided  into  different  classes 
according  to  the  order  either  of  their  juxtaposition  or  of  their  super- 
position, and  the  functional  connexions  attaching  them  to  the  pre- 
ceding are  very  numerous.  We  can  show  this  by  only  a  few  of  the 
most  characteristic  examples. 

Voluntary  reflex  and  automatic  movements.— Our  eyes  sometimes 
look  for  objects  in  the  direction  in  which  they  are  to  be  found  by  move- 
ments which  we  call  voluntary,  and  they  sometimes  passively  receive 
the  luminous  impulses  from  objects  in  front  of  them  ;  but  even  in  the 
latter  case  the  motor  ocular  apparatus  is  not  independent  of  the  visual 
act,  with  this  difference,  that  the  motor  act  then  becomes  instinctive 
or  reflex.  Hardly  has  the  object  to  which  our  attention  is  drawn 
thrown  its  image  on  some  portion  of  the  retina,  than  the  ocular  muscles 
place  the  eye  in  an  appropriate  position  for  receiving  this  image  on 
the  area  of  distinct  vision,  if  it  is  not  already  located  there  (line  of 
fixation  of  the  axis  of  vision).  We  may  add  that  in  ordinary  vision, 
which  is  binocular,  the  movements  of  the  two  eyes  are  mutually  co- 
ordinated for  the  formation  of  images  on  corresponding  points  of  the 
retina.  This  example  shows  in  how  permanent  a  manner  sensibility 
is  solidarized  with  movement. 


VISUAL    INNERVATION  577 

This  dependence  between  sensation  and  movement  and  reciprocally 
exists  in  other  cases  besides  that  of  fixation  of  the  axis  of  vision.  The 
axes  of  vision  in  each  of  the  two  eyes  are  not  in  reality  parallel,  but 
converge  toward  the  object  looked  at,  and  the  convergence  progres- 
sively increases  in  proportion  to  the  nearness  of  the  object.  The  due 
regulation  of  these  convergent  movements  is  assured  by  a  reflex 
association  distinct  from  the  preceding. 

Movements  as  a  whole  ;  internal  movements. — Besides  these  move- 
ments of  the  eyes  as  a  whole,  there  are  yet  others  in  the  interior  of 
the  eyeball  which  are  equally  necessary  for  the  proper  performance  of 
the  visual  fmiction.  These  are  those  which  regulate  the  diameter  of 
the  diaphragm  formed  by  the  iris,  and  hence  the  illumination  of  the 
retina  ;  and  also  the  curvature  of  the  crystalline  lens  for  accommoda- 
tion for  near  vision.  Hence  arise  also  other  reflex  systems,  added  to 
the  preceding  ones,  for  each  of  these  acts  taken  individually. 

All  these  acts  aie  mutually  co-ordinated  in  order  to  operate  as  a 
whole,  but  their  dissociation  is  possible,  and  disease  brings  it  about 
in  different  ways  (Parinaud). 

2.  Different  functional  associations. — The  movements  of  the  ocular 
apparatus,  and  the  associations  of  the  nervous  system  governing  and 
characterizing  them,  may  thus  be  classed  under  four  principal  headings. 
All  are  to  a  certain  extent  of  a  reflex  nature,  whatev^er  may  be  the 
degree  of  associated  consciousness.     These  are  : — 

(1)  Associated  movements  of  direction,  which  maintain  the  parallelism 
(relative)  between  the  ocular  axes  which  is  necessary  for  the  due 
performance  of  binocular  vision. 

(2)  Associated  movements  of  com^erge?ice,  yvhich  determine,  between 
these  axes,  the  value  of  the  angle  which  causes  them  to  cross  on  the 
object  looked  at,  according  to  the  distance  at  which  it  is  si1?uated. 

These  two  varieties  of  movements  are  performed  bj^  the  extrinsic  muscles  of 
the  eye,  and  are  to  son*e  extent  regulated  by  associations  which  exist  in  the 
nuclei  of  the  third  and  the  sixth  pair  of  cranial  nerves.  Their  co-ordination 
^vith  the  movements,  either  of  the  head  or  of  the  body,  in  the  varied  acts  in  which 
they  participate,  necessitates  the  intervention  of  tlie  cerebellum  and  of  the  brain, 
and,  in  tlie  latter  especially,  the  associations  are  different  and  have  different 
seats  aecordmg  to  the  more  or  less  conscious  or  voluntary  natm'e  of  these  move- 
ments. Even  when  the  cerebral  cortex  participates  in  theh-  production,  these 
mo\-ements  are  not  necessarily  Aoluntary,  but  are  freqviently  reflex  or  instinctive. 

(.3)  Movements  of  the  pupil  regulating  the  quantit}-  of  light  which 
enters  the  eye. 

(4)  Alterations  in  the  curvature  of  the  crystalline  lens,  which,  regulate 
the  accommodation  of  the  eye  for  distant  vision.  These  two  last- 
named  are  movements  performed  by  muscles  internal  to  the  eye  itself, 

P.  p  p 


578  SPECIAL    INNERVATIONS 

namely,  the  sphincter  muscle  of  the  iris  and  the  ciliary  muscle  which 
increases  the  anterior  curvature  of  the  crystalline  lens. 

The  two  last  species  of  movement  are  of  an  entirely  unconscious  and  involun- 
tary order.  They  are  dependent  upon  tlie  great  sympatlietic  and  its  bulbo- 
medullary  centres.  As  belonging  to  the  great  sj^mpathetic  ^nust  also  be  con- 
sidered the  elements  contained  in  the  oculo-motor  nerve,  wliich,  leaving  the 
latter,  traverse  the  ophthalmic  ganglion  and  forn-i  tlie  ciliary  nerves  in  connexion 
with  the  cervical  spinal  cord.  These  fibres,  arising  from  a  distinct  portion  of  the 
nucleus  of  the  third  pair,  form  one  only  of  the  origins  (the  highest)  of  the  sym- 
pathetic system.  The  localities  of  association  and  reflexion  of  impressions  which 
control  these  movements  are  graduated  in  the  corresponding  ganglia  of  the 
sympathetic,  in  the  grey  bulbo-medullary  axis,  and  in  the  grey  masses  surmount- 
ing it,  especially  in  the  anterior  corjDora  quadrigemina. 

These  movements  may  be  elicited  both  by  the  optic  thalamus  and  the  cerebral 
cortex.  In  emotional  conditions  the  pupil  is  observed  to  dilate,  and  at  the  same 
time  the  eye  tends  to  project,  so  as  to  protrude  through  the  eyelids. 

This  last  movement  is  due  to  a  parallel  infltxence  (but  one  that  is  fvindamentally 
distinct)  of  the  great  sympathetic  on  the  smooth  muscles  of  the  capsule  of  Tenon, 
and  on  those  which  are  contained  in  the  tliickness  of  the  eyelids,  perpendicular 
to  the  palpebral  cleft. 

The  medulla  oljlongata  through  the  ganglionic  elements  of  the  oculo-motor 
nucleus,  and  tlie  cervico-thoracic  spinal  cord  through  the  fibres  of  the  cervical 
sympathetic  which  arise  therein,  represent  two  antagonistic  influences  acting 
on  the  movements  of  the  pupil  and  on  accommodation.  The  bulbar  influence 
causes  the  sphincter  iridis  (pupillary  contraction)  and  the  ciliary  muscle  (con- 
vexity of  the  crystalline  lens)  to  contract  simultaneously  ;  the  medullary  in- 
fluences causes  the  pupil  to  dilate  and  the  crystalline  lens  to  become  flattened — 
a  double  effect  attributable  either  to  the  inhibition  of  the  sphincter  iridis  and 
ciliary  muscles,  or  to  contraction  of  muscular  layers  wliere  action  is  antagonistic, 
and  whose  existence  seems  to  be  demonstrated,  at  least  so  far  as  regards  the 
pupil  (Grynfeld).  We  may  add  that  the  bulbar  influence  is  not  univocal,  since 
the  trigeminal  contains,  even  in  its  origins,  a  certain  mmiber  of  elements  acting 
in  the  same  manner  as  the  cervical  sympathetic,  and  which  are  hence  connected 
with  the  sympathetic  system  as  a  whole.  It  thus  follows  that  the  pupillary 
mechanism  and  that  of  accommodation  take  their  origin  from  a  great  extent  of 
the  grey  bulbo-medullarj^  axis,  which  conflicts  with  the  hypothesis  of  the  exist- 
ence of  a  cilio-spinal  centre  located  in  a  circumscribed  point  of  the  spinal  cord. 
This  separation  of  tlie  pupillary  nerves  and  tliose  of  accommodation  into  two 
groups  is  connected  with  the  constitution  of  the  great  sympathetic,  whose  nuclei 
of  origin  are  separated  into  distinct  and  discontinuous  masses.  For  the  purpose 
of  mutual  co-operation  these  nuclei  are  connected  by  bundles  appertaining  to 
the  longitudinal  bandalette,  Avhose  fibres  thus  perform  tlie  duties  of  elements 
of  association. 

Photo-mechanical  reaction. —  According  to  Engelmann,  the  action  of  light  on 
the  retina  causes  a  contraction  of  the  pigmentary  cells  and  of  the  internal  seg- 
ments of  the  cones,  which  are,  on  the  contrary,  elongated  in  darkness.  This 
contraction  is  rendered  evident  by  the  comparison  of  two  isolated  eyes  of  an 
animal  (frog),  one  submitted  to  the  action  of  light  and  tlie  other  kejit  in  darkness. 
If  the  intact  animal  is  operated  on,  by  exposing  one  eye  to  the  light  while  the 
other  is  covered  up,  the  contraction  occurs  on  both  sides.  If  the  skin  of  the 
animal  is  brilliantly  illuminated  while  the  eyes  are  in  darkness,  the  result  is  the 
same.  If,  on  the  contrary,  the  brain  be  destroyed  the  photo-mechanical  reaction 
at  a  distance  no  longer  takes  place.     These  facts  seem  to  jorove  the  existence  of 


VISUAL    INNERVATION 


579 


a  reflex  whose  centripetal  and  centrifugal  paths  are  contained  in  the  optic  nerve, 
and  whose  centre  is  situated  in  some  encephalic  ganglion.  Anatomy  teaches  us 
that  centrifugal  elements  are  not  wanting  in  the  optic  nerve  (see  below,  p.  597). 

It  needs  only  to  be  remarked  that,  up  to  the  present,  the  terminal  connexions 
of  these  centrifugal  elements  have  not  been  ascertained  to  exist  with  the  cones, 
but  rather  witli  the  spongioblasts  of  the  retina.  However  this  may  be,  this 
photo-mechanical  reaction  should  be  considered  as  a  reflex  of  adaptation  of  the 
nature  of  the  photo-pupillary  reaction,  wliich  also  is  transmitted  from  one  eye 
to  the  other. 

The  cones,  whicli  have  often  been  called  nerve  elements,  are  (like  the  pig- 
mentary cells  of  the  retina)  epithelial  elements  differentiated  to  subserve  the 
visual  fmiction.  Like  the  cells  of  the  skin,  they  are  outside  the  nervous  system, 
although  in  direct  contact  with  it.  Their  contractile  property,  v/liich  m.ay  be 
compared  with  that  of  certain  epitlielia  in  no  way  prejudices  that  of  being 
strictly  nerve  elements.  The  remarkable  feature  of  this  experiment  is  the  fact 
of  the  initial  stimulation  (by  luminous  radiation)  re-acting,  after  reflexion,  on  the 
same  element  (cone)  which  served  it  as  a  gate  of  entrance.  But  the  mechanical 
movement  in  which  it  is  here  extinguished  is  not  capable  of  causing  this  stimula- 
tion agam  to  arise  in  the  retina,  at  least  in  a  conscious  state.  We  have  proof  of 
this  in  the  fact  that  the  illumination  of  one  eye,  the  other  being  closed,  does  not 
produce  phosphenes  in  the  latter. 

3.  Retino-pupillary  reflex. — When  a  candle  is  brought  near  to  the 
open  eye,  tlie  pupil  will  be  seen  to  shrink  by  the  contraction  of  the  iris  ; 
it     once     more 

,  CMasma  ..:^^ A 

dilates  when  —     ^       ,  \. 

the  light  is  re- 
moved (it  will 
always  be  found 
dilated  if  the 
eye  be  abruptly 
opened  after 
being  closed  for 
some  moments). 
This  is  a  reflex 
act  whose  prin- 
cipal paths  were 
traced  by  Her- 
bert Mayo,  and 

especially  by  I.onget.  These  authors  observed  that,  if  the  optic 
nerve  be  cut,  stimulation  (pinching)  of  the  ocular  end  is  without 
effect  on  the  pupil,  while  that  of  the  encephalic  end  causes  it  to 
contract.  This  is  the  path  of  the  inward  journey.  The  contraction 
is  not  Umited  to  the  pupil  of  the  corresponding  eye,  but  is  also 
observed  in  the  opposite  eye  (Longet)  ;  thus  there  is  passage  of  the 
impulse  from  one  side  to  the  other,  as  occurs  in  many  reflex  acts.  The 
path  of  return  lies  in  the  fibres  of  the  oculo-motor  which  are  given 

r  p* 


Ext.  .J.  body 


—  Ofit.  thai. 


■  Pulviiiar 

Ant.  corpus  quad. 
Post,  corpus  quad. 

Cms.  cerebri. 


Int.  gen.  body 


Fig.  234. — Optic  tracts  and  ganglionic  centres. 
Left  lateral  aspect  {after  Charpj'). 


580  SPECIAL  INNERVATIONS 

o&  from  this  trunk  (thick  and  short  ramification)  in  order  to  pass 
through  the  ophthahnic  ganghon  and  to  reacli,  by  the  ciliary  nerves, 
the  plexus  which  is  situated  at  their  termination  in  the  iris.  These 
are  ganglionic  motor  nerves  of  the  same  nature  as  those  forming  the 
great  sympathetic,  with  which  it  is  convenient  to  connect  them.  The 
path  of  reflexion  has  been  located  by  the  preceding  authors  in  the 
corpora  quadrigemina  (in  mammals),  or  bigemina,  still  called  optic 
lobes  (in  birds).  Their  opinion  is  possibly  supported  by  certain  clinical 
observations,  although  some  authors  consider  that  this  reflex  centre 
should  be  situated  either  in  the  grey  matter  of  the  third  ventricle 
(Bechterew)  or  in  the  ganglion  of  the  habenula  (Mendel). 

Visual  and  reflex  fibres. — Thus  the  optic  nerve  transniits  impulses,  some  of 
which  go  to  the  cortex  to  gi\'e  rise  in  it  to  visual  sensation  ;  others  to  the  cere- 
bellum, to  assist  orientation  ;  and,  lastly,  otliers  are  reflected  en  route,  so  as  to 
ensure  their  return  to  the  iris.  These  impulses  have  not,  perhaps,  exactly  the 
same  starting  point  in  the  retina  ;  tlie  first  may  be  produced  by  shock  of  the 
cones,  and  the  second  by  that  of  the  rods.  In  any  ease,  after  leaving  the  optic 
nerve,  they  follow  two  orders  of  fibres,  two  different  routes.  Tlie  optic  nerve, 
in  the  midst  of  finer  fibres,  which  are  the  visual  fibres,  contains  others  (thicker) 
which  proceed  to  the  cerebellum  and  to  the  anterior  corjDus  quadrigeminum, 
controlling  by  a  reflex  jDath  the  movements  of  orientation  and  of  the  pupil. 
Theii"  respective  attributes  are  rendered  evident  by  the  fact  that  lesions  limited 
to  the  anterior  corpus  qviadrigeminum  leave  vision  intact  and  suppress  the 
pupillary  reflex  (they  also  react  on  the  movements  of  the  eyes)  (Monakow:). 

A  lesion  bearing  upon  the  optic  radiations,  above  the  corpora  quadrigemina, 
causes  blindness,  but  allows  of  the  j^ersistence  of  the  light  reflex  ;  a  lesion  which 
occurs  in  front  of  the  corpora  quadrigemina  abolishes  at  the  .same  time  both 
A-ision  and  the  reflex. 

Hemiopic  pupillary  reaction. —  Should  the  lesion  aftect  the  optic  tract  on  one 
side,  it  causes,  as  is  well  known,  homonymous  hemianoj^sia  ;  the  two  homony- 
mous halves  of  the  retina?  become  insensitive  to  light,  both  from  a  visual  and  a 
reflex  point  of  view  ;  the  other  two  halves  are  sensitive,  and,  if  illuminated,  the 
sensation  of  light  and  the  pu]>illarv  reflex  are  produced  at  the  same  time. 

Reflex  of  accommodation  and  of  convergence. — Reflex  impulses  gaining  the 
pupillarv  muscle  have  more  than  one  source  and  course  ;  these  are  numerous,  as 
is  shown  by  the  following  clinical  fact. 

Argyll-Robertson  noticed  in  certain  diseases,  such  as  locomotor  ataxia  and 
o-eneral  paralysis,  that,  although  the  light  reflex  had  disai^peared,  the  movements 
of  the  iris  (also  reflex)  which  are  connected  with  accommodation  and  with  similar 
movements  causing  convergence  of  the  two  eyes  still  persisted.  These  two 
reflex  cycles  which  functionallj-  produce  the  same  motor  result  (contraction  of 
the  pupils)  and  which  emjjloy  the  same  path  of  return  (ciliary  ramifications 
emanating  from  the  oculo-motor),  have  therefore  distinct  paths  and  a  different 
starting  point. 

4.  Associated  movements. — Thus  we  find  that  there  is  a  reflex  of 
direction,  a  reflex  of  convergence,  a  reflex  of  illumination,  a  reflex  of 
accommodation,  and  to  these  may  be  added  reflexes  of  protection, 
which  we  shall  speak  of  later. 

The  starting-point  of  all  these  reflexes  may  be  retinal  stimulation, 


VISUAL    INNERVATION  581 

and  usually  lies  in  this  stimulation.  If  an  object  is  in  the  field  of  vision 
and  attracts  a,ttention,  both  eyes  are  very  accurately  fixed  on  it  in 
order  to  receive  its  image  on  the  yellow  spot  (reflex  of  direction)  ;  the 
two  ocular  axes  converge  exactly  on  the  object,  so  that  its  image  is 
thrown  on  identical  points  of  the  retina  (reflex  of  convergence)  ;  the 
more  or  less  intense  light  emanating  from  the  object  acts  on  the  dia- 
meter of  the  pupil  (reflex  of  illumination)  ;  the  curvature  of  the  crystal- 
line lens  is  adjusted  so  as  to  give  a  distinct  image  on  the  retina  (reflex 
of  accommodation). 

Far  from  being  absolutely  independent,  each  of  these  reflexes  involves 
the  others  under  certain  circumstances.  The  reflex  of  convergence  is 
connected  with  that  of  accommodation,  and  necessarily  so,  since  the 
effort  of  convergence  and  accommodation  is  exerted  in  the  same  degree 
proportionably  to  the  approach  of  the  object.  These  two  reflexes  in 
their  turn  involve  in  a  certain  measure  the  pupillary  reflex,  and  this 
is  why  in  near  vision  the  pupil  undergoes  a  certain  degree  of  contraction 
independently  of  illumination. 

In  the  hallucinations  of  sight,  changes  of  dimensions  in  the  pupillary 
orifice  may  be  observed,  probably  connected  with  efforts  of  accom- 
modation instigated  by  changes  of  distance  of  imaginary  objects  (Ferre). 

5.  Hemi-oculo-motor  nerves  :  oculo-dextrogyral  and  oculo-levogyral 
nerves. — As  Grasset  has  observed,  simultaneously  with  a  right  hemi- 
opic  nerve  in  connexion  with  the  right  halves  of  the  retinae,  and  a 
left  hemiopic  nerve  which  is  connected  with  the  left  halves  of  the  retinae 
(these  nerves  being  represented  by  the  optic  tract  and  the  optic  radia- 
tion on  each  side),  there  exists  also  in  the  brain  on  each  side  a  hemi- 
oculo-motor  nerve,  which,  being  divided  at  the  periphery  between  the 
two  eyeballs,  turns  them  simultaneously  to  the  right  [dextrogyral  nerve), 
and  also  simultaneously  to  the  left  (levogyral  nerve)  (Grasset). 

The  dextrogyral  nerve  arises  in  the  left  hetnisphere,  and  the  levogyral 
'nerve  in  the  right  hemisphere. — Experiment  has  proved  this,  for  if  an 
oculo-motor  cortical  area  be  stimulated  on  the  left,  the  eyes  turn  to 
the  right,  and  conversely  when  a  right  cortical  area  is  stimulated. 
Clinical  investigation  also  proves  it,  as  after  destruction  of  certain 
parts  of  the  cortex,  a  conjugated  deviation  of  the  eyes  has  been  observed, 
which  results  from  the  paralysis  of  one  of  the  tAvo  hemi-oculo-motor 
nerves.  If  this  destruction  is  seated  on  the  right,  the  eyes  are  turned 
to  the  right  ;  but  if  on  the  left  they  deviate  to  the  left  ;  this  has  given 
rise  to  the  mnemotecbnical  formula  :  "  the  patient  looks  at  his  lesion." 
Paralysis  of  the  motor  area  produces  in  fact  a  deviation  the  direct 
opposite  of  that  produced  by  stimulation  ;  this  paralytic  deviation  is 
due  to  the  persistence  of  an  antagonistic  motor  influence. 


582  SPECIAL  INNERVATIONS 

Comparison  with  the  sensory  path. — We  have  seen  above  that  when  one  of  the 
lobes  of  the  brain  is  destroyed  as  regards  its  visual  area,  the  hemianopsia  is 
homonymous  ;  we  have  just  said  that  in  such  a  case  hemi-oculo-motor  paralysis 
when  it  occurs  is  on  the  contrary  heteronymous,  since  the  paralysed  muscles 
are  those  which  produce  the  movement  to  the  right  when  the  left  hemisphere  is 
injured,  and  reciprocally. 

Comparison  of  the  sensorial  paths  and  the  motor  paths. —  If  the  arrangement 
of  the  sensorial  paths  of  vision  be  compared  with  that  of  the  oculo-motor  paths, 
a  certain  resemblance  will  be  observed  between  thein  ;  but  they  are  far  from 
being  interchangeable.  In  both  we  remark  conducting  tracts  connecting  each 
hemisphere  of  the  brain,  one  to  the  two  right  portions,  the  other  to  the  two  left 
portions  of  each  eyeball  (retina  in  one  case,  muscles  in  the  other).  This  distribu- 
tion implies  a  crossing  of  at  least  a  portion  of  the  conducting  fibres.  This  cross- 
ing as  concerns  the  sensorial  paths  is  a  partial  one,  and  takes  place  in  the  chiasma 
of  the  optic  nerves.  As  regards  the  motor  paths,  it  is  at  first  complete,  but 
becomes  partial  from  the  fact  that  the  impulse  in  order  to  reach  certain  muscles 
(the  internal  recti)  twice  crosses  the  median  line. 

In  fact,  the  dextrogyral  cerebral  nerve  crosses  the  levogyral  cerebral  nerve  in 
the  mesencephalon  to  reach  the  motor  nuclei  of  the  eye.  When  leaving  these 
nuclei  a  part  of  the  fibres  (those  of  the  external  motor  nerve  for  the  external 
rectus  muscle)  remaining  on  the  same  side,  are  direct  ;  another  part  (those 
destined  for  the  internal  rectus),  are  crossed.  In  detail  the  arrangement  differs 
according  to  whether,  with  Uuval  and  Laborde,  we  consider  that  the  fibres  destined 
for  the  opposite  internal  rectus  muscle  start  from  the  external  motor  nucleus  of 
the  same  side,  or  Avith  Spitzka  that  they  take  as  a  starting-point  the  nucleus  of 
the  oculo-motor  also  of  the  same  side.  In  both  cases  they  must  decussate,  and 
the  impulse  which  has  once  surmounted  the  ixiedian  line  with  the  cerebral  nerve, 
when  destined  for  these  fibres  crosses  them  anew  while  following  them. 

Double  crossing. — The  successive  double  crossing  of  the  jiaths  of  the  impulse 
in  the  nervous  system  is  not  an  exceptional  fact  ;  experiinent  shows  that  it  even 
may  be  very  frequent.  An.  exceptional  fact  would  be  for  the  sayne  neuron  to 
undergo  this  double  crossing  in  its  length.  An  example  of  this  is  unkno^vn,  and 
in  the  case  of  the  motor  nerves  of  the  eye,  there  is  a  stage  of  grey  matter  between 
the  two  inverse  changes  of  direction  given  to  the  impulse. 

Thus,  the  hemi-oculo-motor  nerve  conducts  the  impulses  of  one  hemisphere 
to  the  muscles  of  the  two  halves  of  the  eyeball  opposed  to  its  own  situations 
(left  for  right,  and  reciprocally)  and  turns  the  eyes  in  this  direction  opposite  to 
its  own.  The  hemiopic  nerve  conducts  to  one  of  the  heixiispheres  the  impressions 
of  the  two  half  retinae  situated  on  the  same  side  as  itself  (right  for  right,  left 
for  left),  but  the  reversal  of  the  situation  of  the  images  and  of  the  images  them- 
selves in  connexion  with  the  objects  being  granted,  each  hemisphere  sees  the 
objects  placed  on  the  side  opposite  to  itself.  This  remark  holds  good  for  the 
yellow  spot  as  well  as  for  the  peri-macular  area  of  the  retina,  since  the  macu^lar 
tract  acts  in  the  same  way  alone  as  does  the  optic  nerve  as  a  whole. 

Distinct  vision  only  being  possible  in  the  yellow  spot,  the  ocular  axes  are 
directed  instinctively  to  the  centre  of  the  objects  looked  at,  so  that  their  image 
is  thrown  on  the  yellow  spot  :  this  is  the  reflex  of  direction.  This  reflex  of  direc- 
tion has  for  starting-point,  when  the  object  is  situated  laterally,  a  visual  impres- 
sion which  is  made  on  the  halves  of  the  retinae  opposite  to  the  object  (reversal 
of  the  situation  of  the  images)  :  this  impression  is  conducted  to  the  hemisphere 
homonymous  to  these  half  retinae,  and,  like  them,  opposed  to  the  object.  In 
this  hemisphere  it  finds  conditions  of  reflexion  and  motor  paths  which  bring  it 
back  to  the  muscles,  whose  contraction  places  the  yellow  spot  opposite  the  object, 
that  is  to  say,  in  the  prolongation  of  a  straight  line  which  passes  through  the 
centre  of  the  eye  and  the  object. 


VISUAL    INNERVATION  583 

6.  The  elevator  and  depressor  nerves  of  the  axis  of  vision.  —  The 
existence  of  two  hemi-oculo-motor  nerves,  the  one  dextrogyral  and  the 
other  levogyral,  leads  us  to  suspect  the  parallel  existence  of  an  elevator 
and  a  depressor  nerve  of  the  axis  of  vision.  The  dextro-  and  levogyral 
nerves  are  rendered  anatomically  visible  and  independent  by  the  exist- 
ence of  the  interhemispherical  fissure  which  separates  the  brain  into 
two  right  and  left  halves  in  relation  to  the  median  plane.  But  nothing 
of  the  kind  is  found  which  would  suggest  the  existence  of  two  nerves, 
one  of  which  acts  as  an  elevator  and  the  other  as  a  depressor  of  the 
axis  of  vision.  The  fibres  of  both  are  necessarily  distributed  in  the 
axis  of  vision.  The  component  fibres  of  both  are  necessarilj''  distributed 
in  the  two  halves  of  the  brain.  The  two  halves  of  both  are  solidarized 
in  their  functions  by  connexions  which  probably  exist  either  in  the 
two  hemispheres  through  the  commissures  (corpus  callosum),  or  in 
the  mesencephalon  at  the  strengthening  point  between  the  cerebral 
and  peripheral  neurons.  These  two  halves  are  on  the  other  hand 
functionally  independent,  to  allow  of  their  isolated  antagonistic  action. 

7.  Movements  of  the  eye  in  their  relations  with  the  muscles  and  the 
peripheral  motor  nerves. — All  movements  of  the  eyes  except  those  in 
a  transverse  direction  require  associations,  both  nervous  and  muscular, 
which  are  rather  more  complicated  than  those  of  these  latter  ;  this 
fact  stands  out  markedly  from  an  analysis  of  the  movements  of  one 
eye  considered  independently. 

The  movements  of  the  eye  are  all  movements  of  rotation  round  a 
point  coinciding  mth  the  centre  of  the  organ  regarded  as  forming 
a  sphere.  We  will  examine  those  which  are  carried  out  round  the 
three  different  principal  axes  ;  the  antero- posterior  axis  (movement  of 
rotation  of  the  pupil  on  itself)  ;  the  transverse  axis  (movements  of 
elevation  and  depression),  and  the  vertical  axis  (movements  of  abduc- 
tion and  adduction  of  the  pupil).  Three  pairs  of  muscles  (the  four 
recti  and  the  two  obliqtii)  ensure  the  performance  of  these  movements. 
If  each  of  these  pairs  of  muscles  (inferior  and  superior  recti,  internal 
and  external  recti,  superior  and  inferior  obliqui)  were  individually 
situated  in  a  plane  exactly  perpendicular  to  each  of  these  axes,  the 
conditions  of  their  intervention  for  the  production  of  the  before- 
mentioned  movements  (cardinal  movements)  would  be  simple,  and 
from  this  fact  very  distinct.  But  in  reality  only  the  external  rectus 
and  the  internal  rectus  are  in  this  condition.  All  the  other  muscles, 
including  the  inferior  and  superior  recti  (which,  in  fact,  are  oblique), 
form  a  more  or  less  open  angle  with  the  direction  of  the  above-men- 
tioned planes.  Therefore  it  becomes  necessary  that  the  position  of 
the  eye  that  one  of  them,  produces  by  contracting  alone  should  be 


584 


SPECIAL  INNERVATIONS 


corrected  by  the  contraction  of  one  of  the  obhqui  whose  obliquity  is 
in  a  contrary  direction  to  its  own.  It  is  for  this  that  the  inferior 
obhque  is  associated  Avith  the  superior  rectus  to  raise  the  pupil,  and 
the  superior  oblique  with  the  inferior  rectus  to  lower  it. 

For  the  performance  of  diagonal  movements,  that  is  to  say,  of  those 

which  place  the  eye  in  positions  intermediate  between  the  four  cardinal 

positions  above  described,  the  help  of  three  and  not  of  two  muscles 

is  required,  as  may  be  rendered  evident  by  pictures  or  diagrams. 

Antagonism  in  repose. — The  obliqui  muscles  (superior  and  inferior) 

are,  practically,  in  a  certain 
degree  antagonistic  to  the 
recti  (superior  and  inferior). 
They  are  so  not  only  in  a 
state  of  contraction,  properly 
so  called,  for  the  execution 
of  the  movements  of  the  eye, 
but  also  in  the  tonic  condi- 
tion necessary  for  maintain- 
ing the  eye  in  the  orbital 
cavity.  In  fact,  the  four 
recti  by  their  simultaneous 
contraction,  whether  tonic 
or  otherwise,  tend  to  sink  the 
eyeball  in  the  orbit  ;  the 
obliqui,  by  reason  of  their 
situation  and  the  direction  of 
their  insertions,  exert  an 
opposite  tendency  ;  they 
support  the  eye  posteriorly 
like  a  girdle,  and  tend  to 
restrain  it  in  front.  Other  muscular  elements  are  contained  in  the 
ocular  leaflet  of  the  orbital  aponeurosis. 

Individual  centres  for  the  muscles  of  the  eye. — If  from  the  muscles 
we  now  pass  to  the  study  of  the  nerves  directly  controlling  them,  Ave 
may  consider  that  each  muscle  of  the  eye  is,  as  it  were,  provided  with 
a  special  nerve,  by  maintaining,  what  is  indeed  true,  that  each  of  the 
branches  of  the  oculo-motor  nerve  proceeds  from  a  special  centre 
forming  a  portion  of  the  total  centre  of  this  nerve.  Each  of  these 
nerves  may  act  independently  of  all  the  other  nerves  of  the  same  side,^ 
but  not  independent!}^  of  those  of  the  opposite  side.  The  twelve  motor 
nerves  of  the  eye,  or  rather  their  twelve  centres,  are  connected  either 
in  twos,  or  in  a  larger  number,  between  the  two  sides,  independently 


.v.  of  the  ocalo -motor 


.,N.of  Ell.  West 
. .  Princip.  N. 

...Central  N. 
. ,  Dorsal  portion 

...  Ventr.  portion 
.  Fourth  nene 


Nuclei  of  the  oculo-motor  nerve. 


Diagram   showing   their   anatomical    arrangement 
(Charpy). 


VISUAL    INNERVATION 


585 


of  tlie  associations  which  they  mutually  form  on  the  same  side  for  the 
performance  of  the  different  movements  considered  above.  It  will 
be  at  once  obvious  that,  in  these  associated  movements  of  the  two  eyes, 
the  lateral  movements  must  be  distinguished  from  those  of  elevation 
and  depression  of  the  eyeballs.  These  latter  movements  are,  in  fact, 
symmetrical  in  the  ordinary  sense  of  the  word.  The  first-named  cannot 
be  so,  inasmuch  as  a  movement  of  adduction  of  the  eyeball  on  one 
side  must  correspond  Avith  a  movement  of  abduction  of  the  ocular 
globe  on  the  other  side.  To  explain  the  correlated  action  of  the  ex- 
ternal oculo-motor  nerve  of  one  side  with  the  internal  branch  of  the 
oculo-motor  nerve  of  the  other  side,  it  is  held  that  this  branch,  merely 
attached  to  the  oculo-motor  nerve,  arises  in  reality,  by  decussation 
and  crossing  of  its  fibres  on  the  median  line  of  the  bulb  from  the  same 
centre  as  that  of  the  external  oculo-motor  of  the  opposite  side.  Patho- 
logical facts  support  this  manner  of  viewing  the  question.  The  same 
reasoning  holds  good  as  regards  the  branch  of  the  oculo-motor  which 
supphes  the  inferior  obhque  :  it  should  arise  from  the  centre  of  the 
fourth  nerve  of  the  opposite  side. 

Principal  directions  of  the  movements  of  the  ball  of  the  eye,  in  their  relation 
with  the  muscles  executing  them. 


Cardinal  movements. 

Intermediate  movements. 

Participating  muscles. 

Adduction     

.. 

Adduction  and  elevation 

Internal  rectus 
Superior  rectus 
Inferior  oblique. 

Elevation    

Superior  rectus. 

Inferior  oblique. 

Abduction  and  elevation. 

External  rectus. 
Superior  rectus. 
Inferior  oblique. 

Abduction .^ 

, 

■ 

Abduction  and  lowering. 

External  rectus. 
Inferior  rectus. 
Superior  oblique. 

Lowering     

Inferior  rectus. 

Superior  oblique. 

•■ 

Adduction  and  lowering. 

Internal  rectus. 
Inferior  rectus. 
Superior  oblique. 

Some  authors  have  maintained  that,  when  the  head  is  inclined  toward  one 
or  the  other  shoulder,  the  tw^o  eyeballs  perform  a  rotatory  movement  in  the  orbit 
which  is  corrective  of  the  preceding  one.  By  the  help  of  very  exact  data,  it  has 
been  demonstrated  that  this  compensatory  movement  does  not  occur  :  it  is  not 
j^ossible  for  the  eye  to  move  on  its  antero-posterior  axis  (Contejean). 


586 


SPECIAL  INNERVATIONS 


8.  Inhibitory  paths. — Thus  from  the  cortex  (in  the  frontal  and  occi- 
pital areas)  the  impulses  may  descend  through  certain  fibres  of  the 
corona  radiata  and  of  the  internal  capsule  to  the  motor  nuclei  of  the 
muscles  of  the  eye  in  order  to  elicit  movements  of  these  muscles.  These 
exclusively  motor  fibres  have,  nevertheless,  different  functions,  inas- 
much as,  according  to  which  of 
them  is  stimulated,  the  eyeballs 
will  assume  different  positions, 
turning  either  upwards  or  down- 
wards, to  right  or  to  left,  or  else 
assuming  the  intermediate  posi- 
tions. From  the  manner  in 
which  they  distribute  the  im- 
pulse to  the  bulbar  nuclei  of  the 
oculo-motor  nerves,  and  also 
from  the  way  in  which  they  asso- 
ciate the  six  partial  groups  of  the 
fibres  of  these  nerves  (the  six 
nerves  which  proceed  to  the  six 
muscles  of  the  eye)  they  give  rise 
Fig.  236. — Hemioculo-motor  nerves.      to    co-ordinated    movements    of 


cortico-  ^Yie  eyeballs  wliich  are  in  relation 


Bui  bo -muscular    neurons    in    black 
bulbar  neurons  coloured. 

These  latter  neurons  are  of  two  orders,  some   with  their  Special  fuUCtioU.       Like 
excito-motor  as  regards  the  bulbar  nuclei  (in  blue) ;    ,  ■,  ,  <•  i   •    i     ii 

the  others  inhibitory  ks  concerns  these  nuclei  (in   the  motor  arcaS  frOUl  whlch  they 

led).  arise,  thev  represent  these  move- 

The  simultaneoiLS  action  of  the  cortico -bulbar  "  .       .  nn    • 

neurons  of  one  of  the  two   hemispheres  has  the  meuts,     siuCC    it    IS    Sufficient    tO 
effect  of  stimulating  the  nucleus  of  one  side,  and   ^roUSe     their     activity,     CVCU     by 

artificial     stimulation,    for     the 
series    of     the    acts    producing    them    to    be    brought 


inhibiting  that  of  the  other. 


into 


whole 
being. 

Therefore  there  must  be  a  double  motor  cortical  area  to  ensure  the 
arrival  at  the  ocular  muscles  of  impulses  of  various  nature  and  origin  ; 
some,  sensorial,  coming  from  the  retina,  others,  sensory,  coming  from 
the  sensitive  portions  of  the  eye,  or  also  from  other  parts  of  the  sensory 
field  and  from  other  senses  ;  there  must  also  be  in  each  of  these  areas 
functionally  differentiated  fibres  for  the  realization  of  the  different 
co-ordinated  movements  of  the  eyeballs.  This  multiplicity  of  functions, 
each  requiring  a  co-ordinated  system  for  its  performance,  explains 
the  very  extended  development  of  the  cerebral  cortex,  and  also  the 
large  number  of  fibres  of  projection  uniting  it  to  tlie  grey  bulbar  or 
supra-bulbar  masses,  whence  arise  the  nerves  which  directly  supply 
the  muscles.     But  the  complication  of  these  systems  does  not  stop  here. 


VISUAL    INNERVATION  587 

Alongside  of  these  excito-motor  fibres  are  others  possessing  an  inhibitory 
function.  These  elements,  whose  existence  in  the  brain  had  long  been 
suspected,  have  been  demonstrated  by  Sherrington  as  regards  the 
oculo-motor  functions  by  the  aid  of  interesting  experiments.  Here 
are  the  facts. 

Experiment. — In  one  of  the  cerebral  hemispheres  (say  the  left)  in  a  dog  one  of 
the  motor  areas  (frontal  or  occipital)  is  laid  bare  and  stimulated  ;  the  stimulation 
of  this  area  will  cause  deviation  of  both  eyes  to  the  right  (it  must  not  be  forgotten 
that  the  dextrogyral  nerve  starts  from  the  left  hemisphere,  and  the  levogyral 
nerve  from  the  right  hemisphere). 

This  deviation  is  usually  attributed  to  an  excito-motor  action  which,  leaving 
the  cortex,  reaches  in  a  parallel  and  simultaneous  manner  the  internal  rectus 
muscle  of  the  left  eye  and  the  external  rectus  muscle  of  the  right  eye  by  the  motor 
branches  for  these  muscles,  namely  :  the  internal  branch  of  the  left  oculo-motor 
nerve  and  the  right  external  oculo-motor  nerve  of  the  right  eye.  Having  verified 
this,  the  left  oculo-motor  and  the  left  pathetic  nerves  are  cut,  that  is  to  say,  all 
the  motor  nerves  of  the  eyeball  with  the  exception  of  the  external  oculo-motor 
supplying  the  external  rectus.  This  section  (especially  that  of  the  oculo-motor) 
is  performed  with  the  aim  in  view  of  closing  to  the  impulse  all  paths  going  to  the 
internal  rectiis  muscle  of  the  left  eye  ;  the  muscles  thus  deprived  of  their  nerve 
supply  must  be  left  intact,  so  that  their  elastic  tension  may  prevent  the  eye  from 
being  completely  deviated  outwards,  towards  the  temporal  boundary  of  the 
orbit. 

The  same  stimulation  is  again  applied  to  the  same  area  of  the  cortex.  The 
result  is  once  more  a  conjugated  movement  of  both  eyes  to  the  right.  The  right 
eye  tm-ns  rapidly,  tlie  left  eye  slowly,  but  both  deviate  in  the  same  direction, 
that  is  to  say,  to  the  right,  as  before.  How  can  we  explain  this  deviation  of  the 
left  eye  to  the  right,  when  the  internal  rectus  of  this  eye  has  lost  all  comiexion 
with  the  brain,  and  even  with  the  medulla  oblongata,  and  when  the  only  con- 
nexion remaining  between  the  brain,  the  bvilb  and  the  left  eye  is  represented  by 
a  nerve,  the  external  oculo-motor,  supplying  a  muscle,  the  external  rectus,  whose 
contraction  j^roduces  an  exactly  opposite  movement  ?  The  only  admissible 
explanation  is  that  the  impulse  which,  from  the  brain,  proceeds  to  this  muscle, 
has  weakened  the  tone  of  the  latter.  This  tonic  contraction  of  the  external 
rectus  muscle  which  overcame  the  elasticity  of  the  enervated  internal  rectus 
muscle  and  thus  caused  the  left  eye  to  tm-n  slightly  outwards,  having  ceased, 
this  eye  undergoes  a  relative  movement  of  rotation  towards  the  riglit,  a  movement 
which  is  itself  limited  by  the  elasticity  of  the  external  rectus  muscle.  The  devia- 
tion of  the  left  eye  towards  the  right  does  not  in  this  case  result  from  the  activity  of  its 
internal  rectus  muscle,  hut  from  the  lessened  resistance  of  its  external  rectus  muscle, 
this  being  the  only  one,  under  the  conditions  of  the  experiment,  capable  of  being 
influenced  by  the  stimidation. 

Inhibition  by  stimulation  of  the  white  matter. — This  inhibitory  effect  is  ob- 
tained not  only  by  stimulation  of  the  cortex,  but  also,  after  removal  of  the  latter, 
by  stimulation  of  the  corona  radiata,  both  in  the  frontal  and  occipital  region  ; 
or  by  that  of  the  internal  capsule,  when  applied  to  two  points  situated  behind 
the  knee  ;  or,  lastly,  by  that  of  a  section  of  the  corjDus  callosum,  3  to  5  rr.illimietres 
behind  the  knee,  or  in  the  region  of  the  spleniimi. 

Locality  of  inhibition. — The  locahty  in  which  the  inhibitory  pheno- 
menon is  manifested  is  not  then  the  cerebral  cortex,  whose  presence. 


588  SPECIAL  INNERVATIONS 

as  we  have  seen,  is  in  no  way  necessary.  Where,  then,  is  this 
locaHty  situated  ?  It  is  not  located  in  the  spot  where  stimulation  is 
brought  to  bear  ;  that  is  to  say,  at  the  origin  of  the  stimulated 
fibre,  neither  is  it  in  the  ultimate  termination  of  the  motor  system, 
namely,  the  muscle.  It  is  situated  in  the  grey  supra-bulbar  nuclei  at 
the  2^oint  of  union  betiveen  the  fibres  of  the  corona  radiata  and  the  ocido- 
motor  nerves.  It  is  the  tonic  activity  of  these  grey  nuclei  which  is 
weakened  by  the  intervention  of  the  cerebral  inhibitory  fibres.  The 
inhibition  is  effected  by  one  nerve  fibre  on  another,  and  not  by 
a  nerve  fibre  on  a  muscle  ;  but  no  decisive  proof  can  be  brought 
forward.^ 

The  direct  stimulation  of  the  external  oculo-motor,  like  tliat  of  the  other  motor 
nerves  of  the  eye,  or,  more  generally,  of  any  nerve  proceeding  to  a  muscle  without 
interposition  of  grey  matter,  lias  only  one  effect  which  is  invariably  the  same  : 
the  contraction  of  the  muscle  and  never  its  I'elaxation.  For  the  production  of 
an  inhibitory  influence  the  interposition  of  a  nucleus  of  grey  matter  between 
the  segment  of  nerv^e  stimrJated  and  the  muscle  under  consideration  is  required, 
that  is  to  say,  according  to  the  definition  given  of  "  grey  matter,"  the  inter- 
position of  a  locality  in  Avhich,  between  the  terminal  and  initial  extremities 
of  the  neiirons  uniting  this  grey  matter,  that  special  conflict  from  which 
arises  the  suspension  of  motor  activity  characterizing  inhibition  may  be 
effected. 

Another  example. — Sherrington  has  added  to  the  variations  of  his  important 
experiment.  The  oculo-motor  and  the  pathetic  nerves  are  cut  on  the  right  and 
left,  wliile  the  external  oculo-motor  nerves  of  the  two  sides  are  left  intact.  A 
certain  degi'ee  of  divergent  strabismus  ensues  by  the  predominant  action  of  the 
two  nerves  left  unimpaired.  Then  the  two  oculo-motor  areas  of  the  right  and 
left  hemispheres  are  simultaneously  stimulated  :  the  two  eyeballs  are  brouglit 
back  to  tlieir  primary  position,  with  a  certain  degree  of  convergence.  The  same 
reason  and  the  same  explanation  apply  as  given  above.  The  double  stimulation 
thus  brought  to  bear  has  not  been  able  to  restore  the  enfeebled  activity  of 
the  internal  recti,  but  it  has  momentarilj^  suspended  that  of  the  grey  nuclei 
governing  the  external  recti,  and  the  effect  has  been  tlie  same.  When  two  an- 
tagonistic forces  are  contending  for  the  production  of  a  movement,  the  direc- 
tion of  the  latter  may  be  determined,  either  by  increasing  one  force  (which 
is  called  in  neurology  motor  effect),  or  by  diminishing  the  other  (inhibitory 
effect). 

Comparison. — Generalization, — -This  experiment  may  be  compared  with  a 
former  one,  whicli  is  altogether  analogous,  performed  on  the  great  sympathetic 
(in  the  rabbit).  Stimulation  of  the  cervical  segment  of  this  nerve  causes 
contraction  of  the  vessels  of  the  ear,  as  is  well  known  from  the  experiments 
of  CI.  Bernard  and  of  Brown- Sequard.  Stinuilation  of  the  superior  jDor- 
tion  of  the  thoracic  segment  causes  relaxation  of  these  vessels  (Dastre  and 
jNIorat). 

It  may  also  happen  that  tliis  latter  stimulation  may  cause  them  to  contract. 

1  When  the  inhibitory  action  seems  to  be  exerted  at  the  termination  of  the  nerve  in 
the  muscle,  as  in  the  case  of  the  pneumogastric  with  regard  to  the  heart,  it  is  easy  to 
show  that  between  the  nervous  termination  and  the  mviscular  fibre,  grey  matter  is 
interposed  under  the  form  of  gangUa  or  of  a  ganglionic  plexus,  this  being  a  confirmation 
of  the  formula  of  inhibition  as  stated  here. 


VISUAL    INNERVATION  589 

Tlie  thoracic  chain  is  in  fact  (as  regards  the  vessels  of  the  ear)  a  mixture  of  ele- 
ments, some  excito-inotor,  and  others  inhibitorj^  ;  as  a  rule  the  latter  predominate 
in  it.  The  area  of  grey  matter  (in  every  case  according  to  the  definition  given 
of  the  latter)  in  which  the  conflict  between  one  and  the  other  occurs,  is  located 
in  the  sympathetic  ganglia  of  the  base  of  the  neck  (first  thoracic  and  inferior 
cervical  ganglia).  These  two  examples,  one  taken  from  the  great  sympathetic, 
the  other  from  the  enceplialon,  uphold  the  general  conception  which  maj''  be 
held  of  the  mechanism  of  inhibition,  and  which  similar  experiments  have  ex- 
tended to  the  invertebrata  (Physalix). 

Part  taken  by  inhibition  in  the  conjugated  deviation  of  the  eyes. — To  exjjlaiu 
how  the  activity  of  a  single  cerebral  hemisphere  causes  both  eyes  to  deviate  in 
a  manner  which  is  neither  convergent  nor  divergent,  but  mutually  parallel  either 
to  right  or  to  left,  it  has  been  suggested  that  each  hemisphere  possesses  a 
cortico-hulhar  nerve  which,  after  being  reinforced  in  the  bulbar  nuclei,  is  pro- 
longed outwards  by  two  branches,  one  direct,  going  to  the  muscle  on  the 
same  side,  and  the  other  crossed,  proceeding  to  the  muscle  on  the  opposite 
side. 

Theoretically,  this  explanation  appears  sufficient  so  far  as  regards  the  con- 
jugated movements  of  the  eyes,  and  also  of  their  persistent  deviation  in  certain 
cerebral  affections  ;  but  experiment,  having  demonstrated  the  existence  of 
inhibitory  fibres  added  to  the  preceding,  they  must  be  taken  into  account,  and 
a  suitable  position  must  be  found  for  them  in  the  explanatory  scheme.  The 
function  of  these  inhibitory  fibres  cannot  be  simply  and  entirely  to  oppose  the 
preceding,  thus  squandering  and  wasting  the  exciting  and  directing  enei'gy  of 
the  nervous  system  ;  rather  is  their  function  that  of  economizing  this  energj% 
with  the  aim  of  facilitating  and  perfecting  its  activity. 

The  most  general  law  appears  to  be  the  following  one  :  when  two  muscles  con- 
tend for  the  performance  of  a  movement,  once  the  direction  of  this  movement  is  deter- 
mined, a  correlated  action  is  initiated  between  the  inhibitory  fibres  of  the  one  and 
the  excito-motor  fibres  of  the  other.  That  is  to  say,  two  nervous  actions  are  pro- 
duced in  a  jDarallel  and  simultaneous  manner,  one  to  augment  the  exciting  energy 
of  the  muscle  which  is  to  commence  acting,  and  the  other  to  diminish  the  exciting 
energy  of  tlie  opposed  muscle,  and  therefore  its  resistance.  This  at  least  is  what 
would  happen  in  ordinary  functions,  and  what  we  sliould  observe  in  the  cases 
which  are  most  amenable  to  experiment.  Oculo-motor  innervation  is  a  case 
of  this  kind. 

By  analogy  with  the  teaching  of  experiment,  in  the  lateral  conjugated  move- 
ments of  the  eyes  we  may  admit  that  inhibition  intervenes  in  the  elevation  and 
the  depression  of  the  axis  of  vision  ;  the  exciting  influence  of  the  cerebral  elevator 
nerve  on  the  motor  nuclei  which  raise  the  eye  must  be  complicated  by  an  in- 
hibitory influence  of  thislierve  on  the  motor  antagonistic  apparatus  which  tends 
to  prevent  its  rise  or  to  depress  it. 

Inhibitory  and  motor  elements. — The  question  as  to  whether  the  inhibitory  are 
distinct  from  the  motor  fibres,  or  whether  the  same  elements  i^erform,  in  turn, 
both  functions,  has  often  been  matter  of  discussion.  In  principle,  experiment 
and  logic  agree  in  favouring  the  existence  of  a  distinction  between  the  two  orders 
of  fibres  ;  iDut  the  alternative  is  not  so  precise  as  may  appear  at  first  sight.  If 
it  be  remembered  that  the  phenomenon  of  inhibition  is  consummated  at  the 
terminal  extremity  of  the  stimulated  fibre,  and  not  at  its  initial  extremity  in  the 
locality  where  the  stimulation  is  received  ;  and  if  it  be  taken  into  consideration 
that  this  fibre,  at  its  termination,  is  divided  into  distinct  branches,  it  will  be 
obvious  that  the  impulse  which  it  distributes  in  these  branches  may  have  in  one 
of  them  a  stimulating  effect,  and  in  another  an  inhibitory  influence,  according 
to  the  definite  relations  contracted  by  each  of  them  with  the  succeeding  nerve 


590 


SPECIAL  INNERVATIONS 


elements.     The  motor  or  inhibitory  specificity  would  belong  to  the  branches  of 
the  nem'on,  and  not  to  the  neuron  itself.     This  may  apply  to  ocular  inhibition 

in  the  experiment  of  Sherrington  :  a  fibre  of  the 
corona  radiata  bifurcating  in  order  to  proceed  to 
the  nuclei  of  the  external  oculo-motor  nerve  of  tlie 
two  sides  might,  by  one  of  its  branches  (that 
going  to  the  nucleus  of  the  opposite  side)  exert  a 
motor  influence,  and  by  the  other  (the  one  going 
to  the  nucleus  of  the  same  side)  play  an  inhibitory 
part.  Specifically  there  is  nothing  to  prevent  this 
being  so,  because  the  two  branches,  one  motor  and 
the  other  inhibitory,  are  destined  to  constantly 
work  in  the  performance  (by  opposite  means)  of 
strictly  equal  moveinents,  although  these  move- 
ments may  take  place  in  separate  organs  (right  and 
left  eyes). 

For  unsymmetrical  organs,  like  the  heart,  tliere 
is  no  necessity  for  such  an  arrangement. 


Fig. 


237. — Cortico-bulbar 
neurons. 

Their  action  is  at  the  same 
time  excito-motor  as  regards 
the  active  nucleus  and  in- 
liibitory  as  concerns  the  oppo- 
site nucleus  whose  function  is 
antagonistic. 

In  the  case  of  strictly  associ- 
ated movements,  Uke  those  of 
vision,  it  is  siifficient  for  a 
single  neuron  leaving  the  cortex 
to  have,  by  one  of  its  termina- 
tions, an  excito-motor  action  on 
one  of  the  nuclei,  and  by  another 
termination  an  inhibitory  action 
on  the  antagonistic  nucleus. 


9.  Other 
eyes. — The 


co-ordinated  movements  of  the 
lateral  movements  have  an  im- 
portance which  may  almost  be  considered 
as  preponderating,  and  when  the  cortex  is 
stimulated,  they  are  the  movements  by  which 
this  stimulation  is  most  readily  rendered  evi- 
dent. To  demonstrate  the  other  movements  of  the  eyeball ,  it  is  better  to 
eliminate  beforehand  the  influences  giving  rise  to  lateral  movements. 
With  this  end  in  view,  and  if,  for  example,  the  left  hemisphere  is  to  be 
stimulated,  the  internal  rectus  of  the  left  eye  and  the  external  rectus 
of  the  right  eye  should  be  cut.  The  stimulation  will  then,  according 
to  the  point  excited,  give  rise  to  upward  and  downward  movements  of 
the  eyeball  ;  or,  again,  to  movements  in  the  different  quadrants  ;  or, 
finally,  to  those  of  convergence  (J.  S.  R.  Russell). 

It  will  thus  be  obvious  that,  in  the  brain,  motor  elements  for  all  the 
co-ordinated  movements  of  the  eyes  are  present,  these  having  as  their 
object  either  movements  of  the  axis  of  vision  in  all  directions,  or  those 
of  convergence  of  both  eyes  on  objects  which  are  more  or  less  remote. 
To  simphfy  the  classification,  we  may  distinguish  between  a  dextro- 
gyral  nerve,  a  levogyral  nerve,  an  elevator  nerve  and  a  depressor  nerve 
of  the  axis  of  vision,  without  taking  into  account  the  intermediate 
movements  resulting  from  their  combinations  ;  and,  finally,  a  7ierve 
of  convergence,  or  at  least  of  the  association,  which  all  these  different 
movements  and  positions  bring  into  being. 

10.  Movements  of  the  eyelids. — The  membranous  veils  which  are 
lowered  before  the  eyes  to  cover  them  in  sleep,  to  uncover  them  in 
waking,  and  to  protect  and  wash  them  in  winking,  are  themselves  con- 


VISUAL    INNERVATION  591 

trolled  by  antagonistic  muscles  and  nerves,  whose  balanced  or  pre- 
dominating action  determines  their  position  on  the  eyeballs. 

These  muscles  are  the  orbicularis  palpebrarum,  and  the  levator 
palpebrte  superioris.  The  first  is  supphed  by  a  branch  of  the  facial 
-(closure  of  the  eyelids),  the  second  by  a  branch  of  the  oculo-motor 
{opening  of  the  eyelids).  These  two  small  branches,  belonging  to 
•complex  nerves,  enter  into  an  antagonistic  system  which  has  some 
analogy  with  those  of  the  preceding  movements. 

Here,  again,  we  find  numerous  functional  associations  of  the  different 
nerves  and  muscles  of  the  periphery,  and  multiplied  utilizations  of 
^ach  of  these  motor  peripheral  apparatus  according  to  the  functions 
to  be  performed.  When  we  look  upwards,  the  upper  eyelid  is  raised 
so  as  to  uncover  the  eye  and  the  two  movements  are  strictly  correlated, 
a,lthough  at  the  same  time  independent.  It  is  necessary  for  the  will 
to  interfere  in  a  special  manner  in  order  to  close  the  upper  lids  over 
eyes  which  are  voluntarily  raised.  The  branch  and  the  motor  centre 
■of  the  levator  palpebrae  superioris  are  thus  associated  with  the  centres 
of  the  superior  recti  and  the  inferior  oblique  muscles  for  the  perform- 
ance of  the  action  imposed  on  them  by  the  nerve  which  is  the 
elevator  of  the  axis  of  vision. 

Protective  reflex.^ — The  movements  of  the  eyelids  are  comiected 
with  voluntary  acts  as  regards  the  direction  of  the  axis  of  vision,  with 
emotional  acts  in  the  expression  of  certain  sentiments,  but  are  purely 
reflex  in  winking,  which  alms  at  the  protection  of  the  eye.  The  pupil- 
lary reflex  is  in  numerous  instances  (but  not  always)  a  defensive  reflex 
of  nearly  the  same  kind.  If  we  enter  into  the  detail  of  these  actions 
Ave  shall  discover  a  large  number  of  reflexes  of  the  same  nature,  having 
their  ultimate  expression  in  acts  which  are  not  only  motor,  but  also 
secretory,  or,  as  is  sometimes  incorrectly  stated,  trophic.  The  blood 
supply  of  the  eye,  and  especially  of  the  retina,  is  also  regulated  b}^  a 
reflex  mechanism.  Again,  the  eye  is  protected  and  preserved  by 
secretions  both  of  an  external  nature,  as  the  secretion  of  tears,  and  also 
internal,  like  that  maintaining  the  tone  or  ocular  tension  at  its  normal 
level.  The  nervous  agents  which  regulate  these  vascular  and  secretory 
actions  are  located  in  the  trigeminal  and  the  great  sympathetic,  or, 
rather,  in  the  sympathetic  system  whose  origins  are  furnished  by  the 
trigeminal. 

11. — Movements  of  the  head, — When  vision  is  directed  to  an  object, 
Movements  of  the  head  are  often  associated  witli  those  of  the  eyes  in 
order  to  bring  them  to  bear  in  the  desired  direction  ;  the  most  obvious 
of  these  are  the  lateral  movements.  Experiments  have  pointed  out 
the  existence  in  the  motor  region  of  the  cortex  (and  especially  in  the 


592  SPECIAL  INNERVATIONS 

frontal  region)  of  an  area  for  rotatory  movements  of  tlie  head  in  the 
vicinity  of  that  for  movements  of  the  eyes.  In  the  corona  radiata 
there  is  a  dextrogyral  and  also  a  levogyral  nervp  of  the  head,  jnst  as  there 
is  one  of  the  eyes,  and  which  is  placed  in  its  immediate  neighbourhood. 
It  has  been  demonstrated  clinically  that,  in  certain  lesions  of  the  cortex, 
deviation  of  the  head  accompanies  that  of  the  eyes  and  takes  place  in 
a  similar  direction. 

These  nerves  belong  to  two  categories,  thus  resembling  the  muscles 
whose  movements  they  inspire.  These  two  dextrogyral  and  levo- 
gyral nerves  of  the  head  are  totally  crossed  (like  those  of  the  eyes), 
before  reaching  the  motor  nuclei  of  the  nerves  of  the  head  in  the  meso- 
cephalon  (Grasset). 

Some  (posterior  branches  of  the  two  first,  and  anterior  branches  of 
the  four  first  cervical  pairs)  proceed  to  a  group  of  rotatory  muscles  of  the 
head  of  the  same  side,  namely  :  splenius,  large  and  small,  rectus  capitis 
posticus,  and  the  obliquus  capitis  superior.  Others  (external  branch  of 
the  spinal)  proceed  to  a  group  of  rotatory  muscles  of  the  opposite  side  : 
the  sterno-mastoid  and  trapezius.  The  first  proceed  to  their  groups  of 
muscles  without  decussation  ;  the  second,  in  order  to  act  in  correlation 
with  them,  must  cross  each  other  (in  the  same  way  as  the  fibres  of  the 
oculo-motor  proceeding  to  the  internal  rectus  muscle  of  the  eye). 

12.  Numerous  motor  areas  for  the  eye. — The  data  furnished  by  ex- 
periment in  proportion  as  they  become  more  numerous,  show  the  fallacy 
of  the  far  too  simple  conception  which  was  at  first  held  with  regard  to 
the  localization  of  the  sensory  and  motor  functions  in  the  brain.  Con- 
trary to  what  was  originally  maintained,  there  is  not  merely  one  excitable 
7notor  area  in  the  brain,  but  several  such  exist.  In  fact,  in  addition  to 
the  Rolandic  area,  in  which  the  movements  of  the  limbs  and  face  are 
represented,  the  existence  of  another  has  been  ascertained  ;  this  last 
being  situated  in  the  area  of  the  visual  sphere  controlling  the  muscles 
of  the  eyes  ;  and  a  third  will  be  found  in  the  auditory  sphere  which 
governs  the  muscles  of  the  ear.  Nevertheless,  these  data  are  capable 
of  reconciliation  with  the  theory  of  cerebral  localizations,  but  on  the 
condition  that  it  be  expressed  by  a  formula  different  from  the  one 
formerly  made  use  of.  Instead  of  dissociating  and  separating  sensi- 
bility and  motricity,  they  should,  on  the  contrary,  be  strictly  associated 
in  the  execution  of  different  functions,  and,  after  these  have  been  dis- 
tinguished from  each  other  according  to  their  most  obvious  character- 
istics, an  effort  should  be  made  to  discover  if  they  are  represented  in 
any  special  area  of  the  brain.  In  other  words,  localization  must  be 
brought  to  bear,  not  on  the  two  modalities  essential  and  necessary  to 
the  performance  of  the  functions,  but  on  these  functions  themselves. 


VISUAL    INNERVATION  593 

This  new  theory  having  been  formulated,  we  shall  still  find  a  difficulty 
in  accepting  it,  as  even  though  we  may  admit  the  correctness  of  the 
principle,  it  is  not  always  easy  to  decide  about  its  application. 

Motor  occipital  area. — In  the  occipital  lobe,  an  ocular  motor  area 
exists  which  is  more  or  less  interchangeable  with  the  visual  sensory  area, 
and  this  agrees  with  the  idea  we  hold  concerning  the  nature,  essentially 
reflex,  of  nervous  functions  ;  but  in  the  frontal  lobe,  and  therefore  at 
some  distance  from  the  visual  area,  is  another  motor  area  for  the  eyes, 
one  somewhat  distinctly  defined,  and  even  more  easily  experimentally 
excitable  than  the  preceding,  and  which  must  be  taken  into  account 
in  the  cerebral  topography.  If  surprise  is  caused  by  the  sight  of  a 
double  motor  source  converging  in  the  cortex  towards  the  same  inferior 
centres  and  the  same  muscles,  it  must  be  remembered  that  the  same 
peripheral  apparatus  is  often  used  for  very  different  functions.  And 
if  it  be  asked  to  what  reflex  arc  these  oculo-motor  elements  which 
duplicate  those  coming  from  the  occipital  lobe  belong,  we  may  answer 
that  the  ocular  globe,  over  and  above  the  special  sensibility  which 
has  devolved  on  the  retina,  forms  a  portion  of  the  field  of  general  sensi- 
bility, notably  through  the  cornea  and  the  conjunctiva,  these  being 
very  sensitive  surfaces.  No  doubt  the  vicinity  of  these  frontal  oculo- 
motor areas  with  the  tactile  area  of  the  Rolandic  region  is  explained 
by  a  connexion  between  general  sensibility  and  movement. 

Independence  of  the  frontal  and  occipital  areas. — Have  both  motor 
areas  their  fibres  of  projection  in  the  corona  radiata,  or  does  the  stimula- 
tion of  one  of  the  two  simply  follow  the  fibres  of  association  to  reach 
the  other,  and  to  descend  by  a  single  path  into  the  mesencephalic  nuclei  ? 
The  first  of  these  suppositions  is  the  true  one.  To  demonstrate  it  the 
two  areas  must  be  stimulated  after  they  have  been  separated  by  deep 
sections  which  interrupt  the  continuity  of  the  fibres  of  association,  or 
after  the  removal  either  of  the  frontal,  or  the  temporal  lobe  ;  in  both 
cases  stimulation  of  one  or  the  other  will  be  followed  by  motor  effects. 
Further,  it  has  been  olaserved  that  the  excitaT3ihty  of  the  occipital  area 
in  young  animals  precedes  by  several  days  the  appearance  of  that  of 
the  frontal  area.  They  must  then  be  quite  distinct,  and  each  corre- 
sponding to  a  system  complete  in  itself  is  capable  of  operating  in  an 
independent  manner. 

Ophthalmoplegia. — If  it  be  true,  as  some  have  maintained,  that  the  visual  area 
of  the  occipital  lobe  is  blended  with  an  oculo-motor  area,  destruction  of  the  first 
must  involve  that  of  the  second.  Nevertheless,  simple  hemianopsia  after  the 
destrviction  of  the  cuneus,  is  not  followed  by  a  conjugated  deviation  of  the  eyes. 
It  must  be  remarked  with  regard  to  this,  that  paralyses  following  destruction  of 
limited  areas  of  the  cortex  do  not  betray  themselves  by  a  total  or  even  very 
evident  loss  of  movement  in  muscles  connected  with  the  destroyed  area.     The 

P.  Q  Q 


594 


SPECIAL  INNERVATIONS 


resulting  functional  deficiency  takes  effect  only  on  special  modalities  of  the  move- 
ment, allowing  the  pei'sistence  of  a  somewhat  large  number  of  others  ;  this 
explains  the  apparent  integrity  of  the  corresponding  motricity.  The  destrviction 
of  the  two  visual  areas,  like  that  of  the  optic  nerve  itself,  is  only  revealed  by  a 
change  in  the  appearance  of  the  eyes  and  a  vagueness  in  the  glance,  due  to  a  defect 
of  convergence,  and  also  to  the  situation  of  the  eyelids.  These  organs  have 
nevertheless  retained  all  their  mobility,  and  move  under  the  influence  of  im- 
pressions of  a  reflex  natui-e,  or  of  those  furnished  them  by  other  regions  of  the 

brain  and  the  cortex,  this  latter 
being  connected  with  other  senses 
and  functions  besides  that  of  vision 
properly  so  called. 

A  conjugated  deviation  of  the 
eyes  has  been  observed  consecutive 
to  lesions  of  certain  portions  of  the 
cortex  outside  the  visual  area,  using 
the  word  in  its  strict  sense.  Grasset 
and  Landouzy  have  observed  this 
deviation  in  the  case  of  focal  lesion 
of  the  parietal  lobule  at  the  angular 
gyrus  (Grasset),  near  the  foot  of  the 
ascending  parietal  (Landouzy ) . 
Ferrier  has  produced  this  deviation 
by  stimulating  the  angular  gyrus  in 
the  monkey.  Mtuick  has  observed 
a  distm'bance  of  the  ocular  motility 
and  also  of  the  general  sensibility  of 
the  eye  to  be  the  result  of  the  extir- 
pation of  the  inferior  parietal  lobule. 
When  this  region  i  s  artificially 
stimulated,  as  in  J  a  c  k  s  o  n  i  a  n 
epilepsy,  the  deviation  is  naturally 
in  the  opposite  direction. 

Grasset  and  Landouzy  consider 
that  the  cerebral    nerve,   which  is 


Fig. 


and 


238. — Hemioculo-motor  nerves 
centres. 

Cortico-bulbar  neurons  in  blue  ;  bulbo -muscular 
in  black.  \, 

dex,  dextrogyral  oeulo-niotor  nucleus  ;  lev, 
levogyral  oculo-motor  nucleus  ;  PP,  fron  to -parietal 
cortex  (tactile  area)  OO',  occipital  cortex  (visual 
area).  The  tactile  and  visual  senses  make  use  of, 
by  independent  nerves,  the  same  oculo-motor 
nuclei  for  different  functions. 


the  elevator  of  the  uj^per  eyelid, 
also  starts  from  the  inferior  parietal  lobule,  the  destruction  of  this  lobe  being 
sometimes  accompanied  with  blepharoptosis  of  the  side  opposed  to  the  lesion. 
From  the  same  region  of  the  cortex  the  cerebral  nerve  which  governs  the 
antagonistic  movement  of  closure  of  the  eyelids  (opjoosite  side)  is  also  con- 
sidered to  arise  ;  this  nerve  corresponds  to  what  is  called  the  superior  facial 
in  opposition  to  the  inferior  facial  supplying  the  muscles  of  the  inferior  por- 
tion of  the  face,  whose  cortical  area  is  situated  in  the  Rolandic  region.  Exner 
and  Paneth,  by  stimulating  the  angular  gyrus,  have  produced  contractions  of 
the  orbicularis  of  the  opposite  side. 

This  dissociation,  both  anatomical  and  functional,  of  the  two  parts  of  the 
facial,  one  of  which  is  destined  for  the  orbicularis  palpebrarvun,  and  the  other 
for  the  muscles  properly  so  called,  of  the  face,  explains  the  fact  often  noticed 
in  ordinary  hemiplegia  of  the  superior  facial  being  immune  or,  at  any  rate,  less 
markedly  affected  than  the  inferior  facial. 

At  the  same  time,  it  must  be  noticed  that  blepharoptosis  may  also  occur  in 
ordinary  hemiplegia  as  the  result  of  lesion  of  the  central  convolutions,  as  the 
facial  also  possesses  a  source  of  innervation  situated  in  these  convolutions. 

Paralysis  of  the  orbicularis  vasny  also  exclusively  attack  the  voluntary  move- 


VISUAL    INNERVATION  595 

ments  while  ordinary  reflexes  and  the  power  of  closing  the  eyes  during  sleep  are 
preserved.  In  other  cases  the  purely  reflex  movements  are  the  only  ones  re- 
tained. The  reflex  of  occlusion  produced  in  sleep  has  probably  another  locality 
of  reflexion  than  the  basal  ganglia,  possibly  the  cortex  (Tournier). 

Remarks. — Under  the  name  of  ophthalmoplegia  are  clinically  indicated  all 
paralyses  of  the  extrinsic  or  intrinsic  ocular  movements,  whether  the  cause  be 
peripheral  or  central.  It  seems  a  pity  that  the  word  "  ophthalmoplegia  "  has 
not  been  reserved  to  designate  the  ocular  monoplegias  of  central  origin,  as  have 
been  the  words  "  hemiplegia,  paraplegia  "  to  describe  those  paralyses  of  the 
other  organs  whose  origin  is  in  the  spinal  cord  or  the  brain. 

Dissociation  of  the  occipital  motor  area. — Schaffer  (1888),  operating 
on  the  monkey,  has  demonstrated  that  stimulation  of  the  internal 
surface  of  the  occipital  lobe  in  its  medium  region,  produces  lateral 
conjugated  deviation  of  the  eyes  ;  stimulation  applied  to  the  superior 
portion  of  the  occipital  lobe  causes  the  eyes  to  look  downwards,  and 
to  the  inferior  portion  upwards.  (Bechterew  has  noticed  analogous 
facts  resulting  from  stimulating  of  the  anterior  and  posterior  portions 
of  the  same  lobe  ;  only  the  eyes,  instead  of  occupying  analogous  or 
inverse  positions,  were  deviated  towards  the  cpiadrants.)  Also  move- 
ments of  the  eyelids  and  modification  of  the  pupil  may  be  obtained. 
These  partial  localizations,  apparently  so  regular,  of  the  oculo-motor 
cortical  elements,  cannot  fail  to  exercise  an  effect  on  the  minds  of  those 
who  maintain  the  idea  of  a  sort  of  geometrical  projection  of  the  retina 
on  the  visual  area  of  the  occipital  lobe.  Each  of  the  cardinal  points 
of  the  retina  would  be  united  functionally  to  the  muscle  (or  muscular 
group)  which  causes  the  eye  to  deviate  towards  the  four  cardinal  posi- 
tions. Tliis  bond  of  union  would  be  effected  by  a  kind  of  cortical 
reflex  of  direction,  the  luminous  impulses  which  fall  in  the  first  instance 
on  each  of  these  cardinal  points  having  the  effect  of  initiating  the  move- 
ment of  the  corresponding  muscle  in  such  a  way  as  to  place  the  eye  in 
the  position  best  adapted  for  distinct  vision.  Stimulation  applied  to 
the  cortex  would  thus  reach  in  an  isolated  manner  each  of  these  reflexes, 
and  by  bringing  its  niotor  portion  into  play  thus  demonstrate  their 
respective  situation.  This  reasoning  may  perhaps  be  exact,  but  we 
cannot  help  noticing  a  want  of  condensation  about  it  and  also  how 
much  it  stands  in  need  of  support  from  new  data. 

13.  Influence  of  the  cerebellum. — Saucerotte,  in  the  last  century, 
suspected  that  the  movements  of  the  eyes  were  influenced  by  the 
cerebellum.  Magendie  has  observed  that  if  either  the  cerebellar  peduncle 
or  the  pons  varolii  be  cut  the  eyes  are  deviated  downwards  on  the 
corresponding  side,  and  upwards  on  the  opposite  side  to  the  lesion. 
Destructions  and  stimulations  of  the  cerebellum  itself  also  modify  the 
position  and  the  movements  of  the  eyes.     The  ablation  of  a  cerebellar 


596  SPECIAL  INNERVATIONS 

lobe  induces  an  alteration  of  such  a  nature  that  the  eye  of  the  side 
corresponding  to  the  lesion  looks  downwards  and  inwards,  sometimes 
nystagmus  occurs  (the  head,  the  movements  of  which  agree  with  those 
■of  the  eyes,  is  inclined  towards  the  lesion  ;  it  is  twisted  around  its  axis, 
so  that  the  muzzle  seems  to  look  at  the  healthy  side  and  the  occiput  at 
the  side  operated  on).  In  destruction  of  the  vermis  the  eyeballs  are 
the  seat  of  a  vertical  nystagmus  (the  head  is  strongly  inclined  back- 
ward the  trunk  curved  in  the  same  direction  with  opisthotonos,  and 
the  anterior  limbs  are  forcibly  extended)  (Thomas). 

Destruction  and  stimulation  of  the  different  portions  of  the  cerebellum. 

I^ocalized  excitation  of  the  different  lobes  or  portions  of  lobes  on  the 

surface  of  the  cerebellum  produces  principally  movements  of  the 
eyes.  In  stimulation  of  the  lateral  lobe  both  eyes  look  towards 
the  stimulated  lobe  and  at  the  same  time  upwards.  Stimulation 
of  the  flocculus  causes  rotation  of  the  eyes  on  their  antero-posterior 
axes.  In  stimulation  of  the  vermis  in  its  anterior  portion,  the  eyes 
look  directly  upwards,  but  in  that  of  its  posterior  portion  they  are 
directed  downwards  ;  it  being  always  understood  that  the  excitation 
is  applied  exactly  on  the  median  line,  for  should  it  be  displaced  laterally 
the  action  of  looking  upwards  and  below  is  complicated  by  a  displace- 
ment of  the  same  side,  and  these  combined  effects  will  produce  a  diagonal 
position.  In  stimulation  of  the  pyramid  of  the  median  lobe,  the  eyes 
will  move  in  a  horizontal  plane,  directly  to  the  right  should  the  stimula- 
tion be  applied  on  the  right,  directly  to  the  left  if  it  is  applied  on  the 
left  (Ferrier). 

Whatever  be  the  anatomical  relationship  between  the  cerebellar 
cortex  and  the  motor  nuclei  of  the  eyes,  experiment  thus  demonstrates 
in  a  very  obvious  manner  the  existence  of  an  exciting  and  directing 
influence  of  the  cerebellum  on  these  nuclei  and  through  them  on  the 
position  of  the  axis  of  vision.  This  influence  takes  part  in  its  turn  by 
the  help  of  afferent  impulses  conveyed  to  the  cerebellum  by  centripetal 
paths.     The  sources  of  these  stimulations  are  also  numerous. 

A  portion  of  them  come  from  the  retina  (direct  cerebellar  tract  of  the 
optic  nerve),  then  from  the  tactile  organs,  and  especially  from  those  of 
the  eyeball  which  are  irritated  by  their  changes  of  position  ;  lastly,  and 
especially,  from  the  semi-circular  canals. 

Destruction  and  stimulation  of  the  semi-circular  canals. — The  internal 
ear  possesses  by  means  of  its  vestibular  apparatus  a  very  direct  relation 
with  the  co-ordination  of  movements,  those  of  the  eyeball  being  com- 
prised in  it,  this  relation  being  distinctly  demonstrated  by  experiments. 
The  destruction  of  the  labyrinth  is  accompanied  by  nystagmus  and 
ocular  deviation.     This  deviation  much  resembles  that  following  the 


VISUAL    INNERVATION  597 

ablation  of  a  cerebellar  lobe  (deviation  downwards  with  inclination 
of  the  head)  (Thomas).  Stimulation  of  the  circular  canals  in  the 
rabbit  provokes  movement  of  the  eyes  (Cyon).  The  direction  of  the 
movement  varies  according  to  the  canal  stimulated  ;  stimulation  of  the 
horizontal  canal  produces  a  rotation  of  the  eye  of  the  same  side  which 
turns  it  upwards  and  downwards  :  that  of  the  transverse  canal  back- 
wards and  upwards,  and  that  of  the  sagittal  canal  backwards  and 
downwards  ;  in  the  opposite  eye  the  movements  are  feebler  and  made 
in  a  contrary  direction.  Ewald  has  also  found  that  stimulation  of  the 
labyrinth  produced,  it  is  true,  by  a  different  procedure,  acts  on  the 
movements  of  the  eyes  ;  only  the  direction  it  assumes  differs  from  the 
preceding. 

The  relation  between  the  optic  nerve  and  the  orientation  of  the  axis 
of  vision  seems  especially  of  a  conscious  nature  and  its  mechanism 
appears  to  be  principally  cerebral.  That  between  the  labyrinthine 
apparatus  and  the  movement  of  the  eyes  seems  rather  automatic,  and 
of  mesencephalic  and  cerebellar  mechanism. 

Centrifugal  fibres  in  the  optic  nerve. — Tlae  optic  nerve  seems  at  the  first  glance 
to  be  composed  exclusively  of  centripetal  fibres  devoted  to  the  conduction  of 
impressions  received  by  the  retina  for  transmission  to  the  brain.  It  is  in  reality 
a  mixed  column,  which  contains  centrifugal  fibres  though  in  a  small  proportion. 
This  somewhat  unexpected  result,  being  veiy  firmly  established,  deserves  distinct 
attention. 

Origins  and  terminations. — The  optic  nerve  is  then,  thovigh  for  a  long  time 
the  contrary  has  been  believed,  a  mixed  nerve  tract.  From  this  fact  its  section 
produces  complicated  effects,  of  the  same  natiu-e  as  those  following  the  section 
of  a  tract  of  t,he  spinal  cord.  This  section,  in  fact,  cuts  simultaneously  elements, 
some  of  which  are  centripetal  and  others  centrifugal,  and  which  consequently 
proceed  in  opposite  directions,  their  trophic  centres  being,  the  first  in  the  retina, 
and  the  second  in  the  encephalon.  After  this  section,  the  terminal  segn:ients 
undergo  Wallerian  degeneration,  while  the  cells  of  origin  are  the  seat  of  that  of 
Nissl.  For  the  centrifugal  fibres  the  Wallerian  degeneration  is  continued  towards 
the  retina  ;  the  degeneration  of  Nissl  affects,  in  birds,  the  cells  of  the  third  layer  of 
the  optic  lobe,  which  are  thus  termed  trophic  centres,  or  cells  of  origin  for  the  centri- 
fugal elements  of  the  optic  nerve.  As  regards  the  centripetal  fibres  the  degenera- 
tion of  Nissl  affects  the  ganglionic  cells  of  the  retina,  while  the  Wallerian  degeneration 
will  be  propagated  through  the  chiasma  towards  the  optic  lobes  (bigeminal  tuber- 
cule)  whose  whole  investment  of  white  matter  disappears,  in  so  far  as  it  represents 
the  tei'mination  of  the  oj^tic  fibres.  The  neurons  which  leave  the  ojotic  lobe  to 
continue  these  fibres,  and  whose  cells  of  origin  are  situated  in  these  lobes,  feel 
the  rebound  caused  by  the  disappearance  of  the  ojotic  fibres  and  the  resulting 
lack  of  stimulation  for  themselves.  They  do  not  suffer  degeneration  properly 
so  called  ;  they  persist,  bvit  become  atrophied  (atrophic  degeneration,  functional 
atrophy)  (Jelgersma). 

What  is  their  function  ? — As  experiment  tinder  the  circumstances  is  an  im- 
possibility, it  seems  natural  that  the  imagination  should  be  exercised  in  order 
to  find  them  a  probable  function.  At  the  same  time,  however  daring  the  hypo- 
theses formed  in  such  cases  inay  be,  they  only  tend  to  generalize  former  experi- 
ments, and  this  is  what  has  taken  place  here.     The  first  known  type  of  the  nerves 


598  SPECIAL  INNERVATIONS 

called  centrifugal  was  tlie  motor  nerve,  which  causes  the  contraction  of  the 
muscular  fibre.  It  was  supposed  that  nerve  cells  at  whose  contact  these  centri- 
fugal fibres  sioread  out  their  ultimate  ramifications,  without  being  muscle,  pos- 
sessed at  any  rate  one  of  the  properties  of  the  muscular  element,  namely,  con- 
tractility. These  contractile  nervous  cells  would,  according  to  the  disposition 
of  the  impulse  transmitted  to  them,  either  establish  certain  contacts  between 
retinal  elements,  or  else  cause  the  cessation  of  these  contacts,  by  an  alteration 
in  the  distribution  of  the  currents  of  stimulation  in  the  nervous  retinal  network 
and  the  centres  following  it. 

This  hypothesis  errs  not  by  excess,  but  by  want  of  width  of  scope.  It  appears 
to  assume  that  the  motor  nervous  system  onlj^  controls  the  massive  movements 
or  mechanical  phenomena  of  the  living  being  ;  while  in  reality  it  exerts  a  general 
control  over  the  molecular  movements  or  chemical  phenomena  of  the  proto- 
plasm ;  as  proof  of  this  may  be  brought  forward  the  nerves  which  cause  the 
glands  to  secrete  for  the  formation  of  special  products  in  the  centre  of  their  cells. 
These  centrifugal  fibres,  which,  according  to  histology,  only  proceed  to  nerve 
elements,  necessarily  excite  molecular  movements  in  these  elements  in  connexion 
with  tlieir  special  function.  What  is  this  function  ?  We  can  only  answer  that 
for  the  present  it  is  impossible  to  tell.  To  consider  it  as  exckisively  of  a  mechani- 
cal order  would  be  arbitrarily  to  narrow  the  fields  of  possible  suppositions  whose 
number,  apart  from  experiment,  is,  so  to  speak,  unlimited. 

How  is  it  possible  to  he  sure  that  these  nerves,  whose  function  is  unknown,  are 
centrifugal  ? — The  proof  given  is  merely  embryological  and  morphological,  never- 
theless it  appears  convincing.  All  neiu-ons  have  two  poles  which  appear  under 
the  form  of  two  ramified  extremities  of  whose  arborizations  some  collect  the 
impulses  (initial  pole),  and  others  distribute  them  to  the  contiguovis  elements 
(terminal  pole),  and  we  are  able  to  distinguish  these  poles  by  certain  morpho- 
logical characters  (relations  with  the  cell).  When  we  see  in  the  optic  nerve 
neurons  (few  in  number  it  is  true)  having  their  cells  situated  in  the  encephalon, 
and  their  axis-cylinder  arborizations  in  the  retina,  we  say,  without  hesitation,, 
that  these  nerves  are  centrifugal  and  know  we  cannot  be  mistaken. 

Nervi  nervorum. — This  very  unexpected  arrangement  of  centrifugal: 
nerve  elements  terminating  in  a  sensory  nervous  organ  suggests,  as  we 
have  seen  above,  the  hy|Dothesis  of  the  existence  of  an  entirely  new 
class  of  nerves  guiding  the  function  of  other  nerves,  which  has  been 
designated  by  the  name  of  mrvi  nervorum.  It  is  to  be  feared,  however, 
that  this  appellation  will  tend  to  obscure  the  question  instead  of  simpli- 
fying and  elucidating  it.  The  designation  of  vasa  vasorum.  has  been 
bestowed  on  the  small  vessels  which  the  circulatory  system  distributes; 
to  itself  to  nourish  the  tissues  added  to  its  internal  membrane,  this, 
being  from  the  vascular  point  of  view  the  only  essential  function,  and 
of  which  the  coronary  arteries  irrigating  the  myocardium  are  one  of 
the  most  striking  examples.  We  may  also  by  analogy  give  the  name 
of  nervi  nervorum  to  the  nerves  sent  by  the  nervous  system  to  its  own 
special  coverings,  such  as  the  dura-mater,  for  the  performance  of  the 
sensory  or  even  obscurely  motor  functions  of  these  membranes,  and 
indeed  to  any  portion  included  in  the  nervous  system  which  is  not  itself 
of  a  nervous  nature  (protoplasmic  movement  of  the  fixed  cells),  but 


VISUAL    INNERVATION  599 

here  the  comparison  which  so  far  may  be  considered  justifiable  must 
stop. 

The  fact  that  nerve  elements  are  governed  by  other  nerve  elements 
has  long  been  known.  The  nervous  tissue  is  an  organized  system, 
Avliose  different  portions  communicate  the  impulse  to  themselves  in  a 
determinate  direction.  According  to  this  the  sensory  nerves  which 
bring  the  motor  nerves  into  action  for  the  performance  of  a  reflex  act 
would  be  nei'vi  nervorum  ;  but  this  is  not  what  is  impUed  by  the  new 
expression. 

The  signification  of  the  centrifugal  fibres  having  their  termination 
in  the  sensory  elements. — Nevertheless,  it  must  be  universally  felt  that 
the  new  data  brought  forward  through  the  knowledge  of  these  fibres, 
up  to  the  present  time  considered  as  being  aberrant,  is  very  important, 
and  here  is  the  interpretation  I  put  upon  it.  The  scheme  of  the  organi- 
zation of  the  nervous  system  which  has  so  far  held  good,  is  that  of  a 
circuit,  a  circulation  of  impulses  of  which  the  reflex  act  gives  a  good 
idea.  This  circuit  is  generally  regarded  as  being  open  towards  the 
periphery  ;  this,  however,  not  being  usually  true,  since  in  a  number  of 
reflex  acts  the  movement  produced  becomes  again  the  cause  of  stimula- 
tion for  a  movement  of  the  same  nature  (see  Respiratory  Automatism). 
It  is  also  known  that  this  circuit,  which  was  always  previously  supposed 
to  leave  the  periphery  and  to  return  there,  in  reality  is  sunk  more  or 
less  in  the  depth,  the  locality  of  reflexion  being,  for  example,  sometimes 
in  the  ganglia,  sometimes  in  the  spinal  cord,  and  sometimes  in  the  brain, 
according  to  circumstances.  The  centrifugal  fibres  of  the  optic  nerve 
would  give  us  cause  to  imagine  the  individually  completed  existence  of 
reflex  circuits,  whose  starting-point  and  place  of  arrival  are  not  neces- 
sarily at  the  periphery,  but  situated  in  certain  localities  of  the  grey 
matter,  that  is  to  say,  in  the  nervous  system  itself,  at  variable  depths. 

Development  and  excitability  of  the  cortex  of  the  visual  sphere. — In 
an  animal  at  the  moment  of  its  birth,  the  cerebral  cortex  is  generally 
not  yet  excitable  ;  which  is  as  much  as  to  say  that  electrical  stimulation 
brought  to  bear  on  the  Rolandic  region  does  not  provoke  the  well  known 
muscular  reactions  usually  obtained  (Soltmann).  This  excitability  of 
the  cortex  is  only  apparent  after  a  number  of  days,  which  varies  accord- 
ing to  the  animal.  Further,  the  appearance  of  excitability  also  varies 
according  to  the  region  or  cortical  spheres  under  stimulation.  In  the 
dog  excitability  of  the  tactile  area  (Rolandic  area)  only  appears  towards 
the  tenth  day  ;   in  the  guinea  pig,  it  exists  from  birth. 

In  all  concerning  the  visual  sphere  excitabihty  hardly  exists  in  the 
dog  before  the  fortieth  day.  On  the  other  hand  it  has  also  been  proved 
that  it  is  only  at  this  date  that  the  animal  is  caj)able  of  follo^^^ng  or 


600  SPECIAL  INNERVATIONS 

seeking  with  the  eyes  the  object  presented  to  it,  or  that  it  wishes  for. 

These  two  facts,  one  of  observation  and  the  other  of  experiment,  are 
in  agreement  and  explain  each  other  (Steiner).  If  in  the  dog  develop- 
ment of  vision  be  followed  from  birth,  it  will  be  seen  to  pass  through 
the  following  phases  :  at  first  the  eyes  are  shut  ;  towards  the  twenty- 
fifth  day  they  open  ;  nevertheless,  in  spite  of  the  eyes  being  open,  the 
animal  is  still  blind,  as  it  cannot  avoid  objects  placed  counter  to  it. 
Towards  the  thirty-fourth  day  it  avoids  these  objects,  but  does  not  see 
them  unless  they  are  placed  in  the  direction  of  the  visual  axes  ;  it  is 
incapable  of  any  movement  of  the  eyes  to  seek  them.  These  move- 
ments, however,  appear  after  the  fortieth  day,  and  their  appearance 
coincides  with  the  development  of  the  motor  excitability  of  the  visual 
area. 

In  the  same  animal,  hearing  and  especially  smell,  have  an  earlier 
development. 

In  other  animals,  development  of  motor  excitability  in  the  visual 
area  is  also  delayed  behind  that  of  the  motor  area,  although  the  periods 
of  this  development  are,  speaking  generally,  very  different  for  each  of 
these  areas.  Thus,  in  the  cat  and  the  rabbit  excitability  of  the  visual 
area  appears  towards  the  fifteenth  day,  five  days  later  than  that  of  the 
Rolandic  area. 

The  more  perfect  a  function,  so  much  the  more  will  its  complete 
development  require  time  for  its  evolution.  We  may  thus  explain  the 
differences  observable  between  one  area  and  another  in  the  same  sub- 
ject, and  also  between  the  same  area  in  different  animals  and  even  in 
different  individuals. 

In  an  infant  it  is  only  from  the  fifth  week  that  the  eyes  are  fixed  on 
objects  coming  into  the  prolongation  of  the  visual  axis.  It  is  only  at 
the  fifth  month  that  the  infant  follows  with  the  eyes  or  seeks  with  them 
for  objects  situated  or  moved  about  before  him  (Rahelmann).  Accord- 
ing to  all  probability,  it  is  then,  and  only  then,  that  his  visual  cortex 
would  be  found  to  be  excitable,  if  it  were  possible  to  examine  it  elec- 
trically, as  in  the  preceding  experiments 


CHAPTER    III 


AUDITORY    INNERVATION 

Of  all  the  specific  innervations,  auditory  innervation  is  perhaps  the 
highest  and  the  most  perfect  :  it  is  far  from  being  the  best  knowTi  ; 
but  the  sense  of  hearing  in  the  human  species  appears  to  acquire  in 
connexion  with  the  function  of  spoken  language  (which  all  men  possess) 
an  importance  even  exceeding  that  of  the  sense  of  sight.  Again,  in 
this  system  there  is  a  differentiation  marked  bj^  a  dissociation  between 
an  element  common  to  all  sensation,  the  idea  of  exteriorization,  or,  to 
put  it  better,  of  exterior  localization,  and  the  conception  of  specific 
sensation,  which  is  here  audition  properly  so  called. 

Comparative  anatomy  and  physiology. — Embryologically  the  auditory  appara- 
tus is,  like  that  of  the  other  senses,  derived  from  the  ectoderm.  Fvmctionally, 
it  is  a  transformation  of  the  tactile  apparatus  adapted  to  the  analysis  of  pressures 
and  of  special  movements.  We  see  it  gradually  advancing  towards  the  specific 
form    it  possesses  in  the    superior 

vertebrata.        Further,     it    retains  "^ 

even  in  them,  first  traces  of  itg 
tactile  function.  This  function 
has  remained  visible  more  especially 
in  the  vestibular  portion  of  their 
labyrinthine  apparatus,  the  origin 
of  which  is  far  older  than  that  of 
the  strictly  auditory  portion. 

In  the  coelenterata  this  apparatus 
is  roughly  sketched  under  the  shape 
of  a  vesicule  constructedjaf  neuro- 
epithelial cells  which  contains  in- 
ternally a  solid  mobile  mass — the 
otolith.  In  Medusce  the  ptocystic 
formations  k  n  o  w  n  as  auditory 
vesicules     appear,     with     ciliated 

pavement  cells  facing  internallj%  connected  by  nerves  to  a  nerve  ganglion,  and 
this  in  its  tm-n  to  muscles  :  the  reflex  sensorial  arc  is  already  formed  (Beaunis). 

Such  is  the  primordial  apparatus,  which  in  invertebrata  may  present  fairlj- 
diverse  forms  (open  or  closed  vesiciile,  single  or  multiple  otolith,  etc.),  and  to 
which  elaborated  portions  tend  to  be  added. 

In  fish  the  ear  is  composed  of  a  labyrinth  with  a  central  cavity  or  vestibule, 
possessing  an  utriculus  and  three  semicirciilar  canals,  but  no  cochlea. 

In  snakes  a  rudimentary  cochlea  appears,  but  is,  however,  reduced  to  a  Cjuarter 
of  a  turn.     In  these  animals  the  cerebellum  is  verj-  little  developed. 

601 


Fig.  239. — Auditory  organ  of  the  Rhopa- 
lonenia  still  showing  a  small  orifice 
(Hertwig). 

hJc,  modified  tentacle  ;    o,  auditory  organ. 


602 


SPECIAL  INNERVATIONS 


In  birds  the  semicircular  canals  are  highly  de^•eloped,  the  cochlea  generally 
remains  rudimentary,  but  the  cerebellum  assumes  a  somewhat  high  development. 

In  mammals,  the  auditory  apparatus  is  complete  as  in  man.  The  vestibule 
communicates  on  one  hand  with  the  semicircular  canals,  and  on  the  other  with 


Fig.   2-40.— Otocyst  of  Unio. 
acoustic  nerve  ;   h,  capsule  of  the  otocy.st 


in  which  it  ramifies  ; 
d,  otolith. 


c,  vibratile  epithelium  ; 


Fig.   241. — Organ  of  hearing  in  Barinaria. 
17,    acoustic    nerve  ;     h,    epithelium    of   the 
otocyst  ;    c,  ciliated  papillse  (auditory  hairs)  ; 
(/,  otolith. 


the  coclilea.  The  sonorous  waves  in  them,  having  become  aerial,  are  propa- 
gated to  the  internal  ear  through  a  cavity  (middle  ear),  after  having  been  con- 
densed by  a  trumpet  (external  ear). 

Labyrinth. — The  aggi-egation  of  cavities  forming  the  internal  ear  is  the  labj^- 
rinth.  Here  may  be  distinguished  a  middle  portion  (vestibule)  conimunicating 
with  two  other  series  of  cavities  (semicircular  canals  on  the  one  hand,  cochlea 
on  the  other).  The  vestibule  contains  two  orifices  closed  by  elastic  membranes, 
which  form  a  mobile  separation  between  it  and  the  cavity  of  the  tympanum. 
This  assemblage  of  cavities  is  filled  with  a  liquid  (perilymph).  Any  pressvu*e 
brought  to  bear  on  one  of  these  two  membranes  will  cause  this  liquid  to  oscillate 
by  depressing  one  while  the  other  imdergoes  an  opposite  movement.  This  is 
precisely  what  is  done  by  the  chain  of  ossicles  which  by  its  ultimate  portion 
(stapes)  is  attached  to  the  membrane  of  the  fenestra  ovalis  and  transmits  to 
the  ossicles  the  movements  of  the  membrana  tympani  wliich  is  caused  to  vibrate 
by  the  contact  of  the  sonorous  waves. 

The  osseotis  labyrinth  is  throughout  lined  by  a  soft  membranous  investment, 
the  membranous  labyrinth,  which  is  exactly  adjusted  to  its  cavities  and  is  filled 
with  liquid  (endolymph)  ;  it  is  separated  from  the  osseous  wall,  to  which  it  only 
adheres  at  the  site  at  which  the  nerve  fibres  jjenetrate,  by  another  fluid  (peri- 
Ijrmph),  in  such  a  way  that  the  whole  system  is  filled  by  these  two  layers  of  liquid, 
which  are  capable  of  influencing  each  other  mutually  through  the  thin  membrane 
which  separates  them.  It  is  this  membrane  wliich  transports  to  certain  special 
localities  the  ciliated  nerve  terminations  which  collect  the  excitation. 

The  liquid  current  thus  produced  in  the  vestibule  is  conveyed  in  the  cochlea 
and  in  the  semicircular  canals.  The  characteristic  structure  of  these  organs 
impart  to  the  impulse  special  directions  and  movements.     The  cochlea  is,  as 


AUDITORY  INNERVATION  603 

its  name  indicates,  a  cone  rolled,  as  it  were,  on  its  axis  ;  but  this  cone  is  double, 
being  divided  by  a  median  partition  into  two  parallel  scalse  communicating 
above,  of  which  the  bases  or  inferior  orifices  open,  the  one  into  the  vestibule 
towards  tlie  fenestra  ovalis  (scala  vestibuli)  and  the  other  towards  the  fenestra 
rotvinda  (scala  tympani).  Thus  the  liquid  in  its  undulatory  movement  through 
the  cochlea  has  the  benefit  of  a  double  route  through  the  latter.  Between  the 
two  scalae,  incoinpletely  separated  the  one  from  the  other  by  the  lamina  spiralis, 
a  third  of  a  membranous  nature  formed  by  the  prolongation  of  the  membranous 
labyrinth  is  found,  which,  in  the  semblance  of  a  slightly  flattened  internal  tube, 
completes  the  partition  formed  by  the  lamina  spiralis.  This  is  the  membrane 
of  Corti,  in  which  the  ultimate  brandies  of  the  acoustic  nerve  come  to  an  end. 
This  mobile  laj'er  receives  the  rebound  of  the  undulations  of  the  liquid  and  trans- 
mits it  to  the  extremities  of  the  nerves  contained  in  it.  It  collects  them  in  its 
different  portions  according  to  the  pitch  of  the  sound  (Xuel,  Bonnier).  Shrill 
sounds  will  take  origin  towards  the  base  of  the  cochlea,  and  deep  sounds  towards 
its  summit. 

In  the  vestibule  itself , in  the  saccule, the  wave  resulting  from  the  displacement  of 
the  liquid  strikes  the  crista  acustica.  This  is  the  name  given  to  projecting  por- 
tions of  the  saccular  membrane  which  are  provided  with  cilia,  and  also  furnished 
with  nerve  terminations.  Placed  in  opposition  to  the  liquid  current,  like  a  kind 
of  dyke  which  may  also  be  submerged,  they  receive  from  it  an  impulse  wliich  is 
strengthened  by  the  displacement  of  the  otocones,  these  being  a  sort  of  dust  or 
grit  of  extreme  tenuity  which  is  agitated  by  this  liquid. 

Finally,  there  is  an  ebb  and  flow  at  the  orifices  of  the  semicircular  canals,  and 
therefore  currents  which  pass  through  them  ;  these  currents  are  also  a  source 
of  excitation  for  the  nervous  currents  ending  therein. 

A.     LABYRINTHINE    EXCITATION 

The  excitation  we  call  auditory  is  of  a  complex  nature  :  it  conveys 
to  us,  in  addition  to  the  specific  tonal  sensation  of  hearing,  other  un- 
conscious or  subconscious  impressions  which  play  a  most  important 
part  in  the  formation  of  our  idea  of  space.  From  this  point  of  view 
audition  may  in  a  certain  degree  be  compared  to  touch,  in  which,  to- 
gether with  cutaneous  sensibility,  a  less  distinct  sensation  of  deep  origin 
whieh  is  called  the  muscular  sense,  is  associated  ;  but  in  auditory  in- 
nervation the  specialization  of  the  two  functions,  that  is  to  say,  the 
dissociation  of  the  idea  of  space  from  the  specific  sensation  is  carried  a 
great  deal  farther. 

Uniform  modality  of  the  excitation. — The  three  apparatus,  of  such 
very  distinct  geometrical  form,  composing  the  internal  ear,  or  laby- 
rinth, all  receive  the  impulse  in  a  similar  manner,  and  the  method 
originates  in  tactile  excitation  by  contact  or  by  rubbing.  An  aerial 
wave  causes  the  tympanic  membrane  to  vibrate  ;  it  is  transformed 
into  a  solidarized  movement  of  the  chain  of  ossicles,  it  gives  rise  to  a 
displacement  and  liquid  currents  in  the  labyrinth,  and  the  nervous 
papillae  of  the  latter,  analogous  to  those  of  the  dermis,  are  stimulated. 
It  must  be  admitted  that  this  form  of  stimulation  is  more  comprehen- 
sible than  that  suggested  by  Helmholtz,  which  attributes  to  fibres  of 


604 


SPECIAL  INNERVATIONS 


microscopic  dimensions  the  possibility  of  vibrating  separately,  accord- 
ing to  their  length,  in  conformity  with  the  pitch  of  the  sound  emitted. 
Different  appropriations. — This  uniform  method  of  excitation  of  the 
nerves  of  the  ear  by  external  pressure,  alternately  positive  (condensing 
wave)  and  negative  (rarefying  wave)  is  utihzed  for  the  purpose  of  effect- 
ing different  analyses  in  each  part  of  the  labyrinth.  In  the  cochlea, 
the  collected  impulse  determines  the  auditory  sensation.  In  the  semi- 
circular canals,  the  impulse  is  united  to  the  notion  of  direction  or  sense 
of  space.  In  the  vestibule  the  nature  of  the  impulse  is  in  some  degree 
of  a  mixed  character,  and  participates  in  that  of  both  the  preceding. 


Facial  y. 


Sup.  br.  reHib.—- 
N. 


CocU.  N. 


Br.  inf.  xtitib.  - 
N. 


■'~^ucc.  N.    jV.  to  pjst.  s.-circ. 
canal 


Fig.  242. — Mode  of  ramification  of  the  auditory  nerve  (after  Retzius). 
Right  membranous  labyrinth,  seen  posteriorly. 


Far  from  being  limited,  to  hearing  alone,  the  apparatus  we  call  auditory 
furnishes  us  with  varieties  of  information  other  than  those  by  which  it  analyses 
sound  ;  it  possesses,  as  it  were,  a  certain  number  of  secondary  functions  derived 
froin  its  method  of  excitation,  such  as  has  been  explained  above.  Bonnier 
attributes  to  it  the  following  functions  in  particular  : — - 

Baresthetic  function. — By  it  the  animal,  whatever  be  the  species,  under  con- 
sideration, possesses  the  power  of  estimating  the  pressure  exercised  on  it  by  the 
external  medium,  be  it  aerial  or  liquid,  in  which  it  lives. 

The  liquid  (perilymph  and  endolymph),  shiit  up  in  the  closed  cavity,  or  rigid 
portion  of  the  labyrinth,  has  no  tension  of  its  own  in  this  cavity,  but  arrange- 
ments exist  there  which  ensure  it  (normally)  equality  of  tension  with  the  external 
medium.  Thus  it  will  reflect,  either  the  constant  state  of  this  pressure,  or  its 
variable  conditions  (during  shocks).     It  is  true  that  there  are  canals  of  derivation, 


AUDITORY  INNERVATION 


605 


but  these  are  too  delicate  to  allow  of  the  exit  en  masse  of  the  labyrinthine  lymph, 
but  on  the  other  hand  they  are  sufficient  to  re-establish  compensation  when  the 
difference  of  tension  becomes  too  strong.  Other  protecting  mechanisms,  like 
the  muscle  moderating  the  pressure  of  the  stapes  on  the  fenestra  ovalis,  are  also 
adapted  to  diminish  the  effects  of  exaggerations  of  external  pressure  and  so 
preventing  the  ruptiu-e  of  the  membranes  of  the  labyrinth  which  would  ensue. 
However  that  may  be,  we  possess  an  apparatus  which  instructs  us  with  regard 
to  the  state  of  external  pressure  and  its  variations. 

The  resulting  sensations  are  not  conscious  ones,  they  only  become  so  when 
reaching  a  condition  of  discomfort  apiDroaching  pain,  or  indeed  of  pain  itself. 
They  nevertheless  act  on  us  as  a  source  of  internal  excitation  and  may  modify 
ovir  general  aptitude. 

Manaesthesic    function. — If  the  internal  pressvu-e  of  the  labj^rinthine  Ij^mph 


Fig.  243. — Diagram  of  the  internal  ear. 

RT,  scala  tympani  ;  RV,  scale  vestibuli  ;  CC,  cochlear  canal ;  OC,  organ  of  Corti  situated 
on  the  basilar  layer  which  separates  the  scala  tympani  from  tlie  scala  vestibuli  ;  GC,  ganglion 
of  Corti  in  the  canal  of  Rosenthal  ;  Si,  saccule  ;  UT,  utricule  ;  VA,  anterior  serai-circular  canal  ; 
VP,  posterior  semi-circular  canal  ;  ma,  auditory  maculae  of  the  utricule  and  saccule  ;  ca,  auditory 
crests  of  the  ampullse  of  the  semi-circular  canals  ;  GS,  ganglion  of  Scarpa.  It  has  not  been 
possible  to  rejDresent  the  horizontal  canal  which  is  perpendicular  to  the  preceding  (after  M. 
Duval). 


(which  has  its  immediate  source  in  the  pressure  of  the  arteries  distributed  to  it) 
becomes  in  certain  conditions  too  high,  the  internal  ear  acts  as  a  plethysmograph 
and  its  sensory  nerves  register  this  pressiu'e  according  to  its  conscious  or  im- 
conscious  manifestation  and  also  its  degree.  The  liquids  of  the  labyrinth  (peri- 
lymph and  endolymph)  are  not  humoui's  of  a  permanent  nature,  but  like  all 
analogous  liquids  are  submitted  to  a  slow  circulation  which  renews  them.  Pro- 
duced in  the  canals  by  secretion  of  the  endothelium  wliich  lines  the  latter,  they 
are  suspended  in  the  lymphatic  spaces  of  the  dura-mater  and  the  subarachnoid 
membrane. 

The  equilibrium  between  their  production  and  distribution  is  regvilated  by  a 
reflex  vaso-motor  and  secretory  excitation,  which  is  itself  regulated  by  the  pres- 


(506 


SPECIAL  INNERVATIONS 


sure.  Disturbances  of  this  mechanism,  as  regards  any  of  its  factors,  will  induce 
abnormal  variations  of  the  internal  labyrinthine  pressure  with  its  consequences 
(buzzing  in  the  ears,  vertigo,  nausea,  vomiting,  etc.),  which  are  caused  by  rever- 
beration of  the  sensory  excitation  either  on  the  bulbar  nuclei  or  others. 

Seisaesthesic  function. — The  abrupt  and  rhythmic  variations  of  the  pre.ssiu'e  of 
the  external  medium  are  also  registered  in  the  internal  ear  like  the  preceding, 
which  we  have,  in  the  first  instance,  supposed  to  be  slow  and  isolated.  This  will 
be  the  same  excitation  become  periodic. 

a.  Vestibule. — This  seissesthesic  function  which  registers  the  vibra- 
tions of  whatever  kind  appertains  to  the  vestibule,  and  more  especially 
to  the  utricule.  Its  membrane  (fenestra  ovalis),  shaken  by  the  stapes, 
communicates  its  vibrations  to  its  liquid,  and  by  it  to  the  crista  acustica. 
The  resulting  sensations  are  not  hearing,  properly  so  called,  but  a 
phenomenon  which  is  prepared  there  and  which  will  become  hearing  in 
the  differentiated  apparatus  of  the  cochlea.     These  sensations  are  the 


Fig.  "244. — Structure  of  the  organ  of  Corti. 

AX,  axis  of  the  cochlea  ;  MB,  basilar  membrane  ;  in,  its  insertion  in  the  free  border  of  the 
spiral  osseus  membrane  ;  ex,  its  external  insertion  ;  TC,  tunnel  of  Corti  ;  PL,  its  internal  pillar  ; 
PE,  its  external  pillar  ;    AR,  articulation  of  the  two  pillars. 

AI,  internal  ring,  giving  passage  to  the  hairs  of  the  internal  acoustic  cell  ;  SI,  cell  of 
external  support  ;  EP,  indifferent  epithelium  ;  CD,  cells  of  external  support  forming  by 
their  prolongation  the  articular  membrane  cc  whose  orifices  give  passage  to  the  cilia  ca  of  the 
external  acoustic  cells  or  those  of  Corti. 

CX,  cellular  bodies  of  acoustic  neurons,  situated  in  the  canal  of  Rosenthal  (ganglion  of  Corti). 
One  of  them  has  its  receptive  arborizations  in  an  internal  acoustic  cell  ;  tiie  other  in  the  external 
acoustic  cells  (after  M.  Duval). 


hearing  of  the  invertebrata  or,  at  any  rate,  in  them  take  the  place  of 
hearing.  They  are  very  general,  and  may  be  found  in  man.  It  is 
these  which,  in  a  deaf  person  deprived  of  cochlear  audition,  permit 
him  to  perceive  the  vibrations  of  a  tuning-fork  placed  on  the  skull  or 
on  the  mastoid  apophysis  (Bonnier). 

b.  Cochlea. — The  function  of  the  cochlea  is  very  complex  and  its 
mechanism  is  still  obscure.  In  embryological  and  functional  develop- 
ment it  is  the  last  to  put  in  an  appearance  ;  it  is  the  most  differentiated 
and  most  conscious  portion  of  the  auditory  apparatus  taken  as  a  whole, 
and  for  this  reason  it  disguises  the  others,  which  can  only  be  revealed 
by  an  analysis  external  to  the  subject  itself.     We  shall  examine  it  in  a 


AUDITORY  INNERVATION  607 

special  manner  with  regard  to  the  senses  properly  so  called  and  their 
organs.  The  cochlea  also  collects  vibrations  whose  mode  of  origin  and 
propagation  is  not  essentially  different  from  that  of  the  preceding. 

These  vibrations  are  fused  together  in  the  nervous  system,  which 
contains  their  initial  expansions.  They  give  rise  in  it  to  a  continuous 
sensation  which  is  called  the  sonorous  sensation.  This  consequently 
proceeds  from  a  periodic  repetition  of  the  excitation  and  is  only  brought 
into  being  when  the  rhythm  is  comprised  between  certain  limits,  the 
one  minima  (32)  and  the  other  maxima  (76,000  vibrations  to  the  second). 
In  music  hardly  any  sounds  are  employed  except  those  comprised 
between  40  and  4,000  oscillations. 

c.  Semicircular  canals. — The  semicircular  canals  make  their  appear- 
ance in  the  zoological  series  long  before  the  cochlea  ;  they  are  a  much 
less  marked  differentiation  of  the  tactile  sense  than  is  the  latter.  They 
are  found  in  the  lamprey  and  the  myxinodes  ;  they  are  highly  de- 
veloped in  fishes.  In  man  and  the  larger  number  of  the  vertebrata  they 
exist  to  the  number  of  three,  orientated  in  three  f  lanes  which  recall  the 
three  directions  of  space  :  one  is  vertical  and  superior,  that  is  to  say, 
raised  above  the  two  others ;  it  is  perpendicular  to  the  crest  of  the  petrous 
portion  ;  the  other  is  vertical  and  posterior,  it  is  parallel  to  the  axis  of 
the  petrous  portion  ;  the  last  is  horizontal  and  external.  The  three 
canals  are  perpendicular  the  one  to  the  other  reciprocally.  At  their 
point  of  communication  in  the  vestibule  these  canals  present  ampullary 
dilatations,  at  the  site  of  these  dilatations  their  membrane  presents  a 
ciliated  epithelium  and  a  neuro-epithelium  in  connexion  with  the  rami- 
fications of  the  vestibular  nerve.  We  have  already  said  that  these 
canals  receive  their  portion  of  the  excitation  produced  by  the  aerial 
wave  which,  by  the  play  of  the  tympanic  membrane  and  the  ossicles, 
displaces  the  labyrinthine  lymph.  This  excitation,  which  never  gives 
rise  to  the  sonorous  sensation,  is  utilized  for  furnishing  the  subject 
with  ideas  of  another  description  relative  to  his  attitude,  and  his  orien- 
tation in  the  surrounding  medium.  These  ideas  are  related  to  what 
is  known  as  the  sense  of  space. 

2.    The  Sense  of  Space 

The  relation  of  the  semicircular  canals  to  equihbrium  was  fu'st 
noticed  by  Flourens  in  1824.  Goltz,  Breuer  and  others,  when  repeating 
these  experiments  endeavoured  to  give  a  rational  explanation  of  this 
relationship.  De  Cyon,  in  1874,  was  the  first  to  speak  of  a  sense  of 
space  and  connected  with  the  more  general  conception  of  such  a  sense 
all  the  different  experiments,  including  his  own.  In  the  midst  of  dis- 
cussions and  criticisms,  the  new  idea  gained  ground  and  the  expression 


608 


SPECIAL  INNERVATIONS 


held  good.  The  question  was  taken  up  by  M.  Duval  and  Laborde, 
and  a  number  of  foreign  authors,  Ewald  being  amongst  them.  It  is 
to  Bonnier  that  we  owe  the  best  analysis  of  the  phenomenon  of  the 
formation  of  images  in  space  and  the  most  lucid  outline  of  this  complex 
question.^ 

1 .  Excitations  of  extrasomatic 
origin — Exteriorization  and 
localization  in  s  p  a  c  e. — W  e 
possess  the  faculty  of  distin- 
guishing the  origin  of  the  aerial 
waves  which  reach  us  and  which 
we  call  sonorous,  in  virtue  of 
the  sensation  developed  by 
them  in  a  specific  portion  of  our 
nervous  system.  We  experi- 
ence a  sensation  and,  as  in  all 
the  other  senses,  we  exteriorize 
and  localize  in  space  the  origi- 
nal cause  of  the  impression 
and  sensation  experienced. 
The  process  of  localization  is  a 
complex  one,  but  its  principal 
mechanism  is  contained  in  the 
semi-circular  canals,  or,  in 
other  words,  in  an  apparatus  annexed  to  that  of  audition,  but  dis- 
tinct from  it. 

According  to  the  direction  of  the  aerial  wave,  the  tympanic  mem- 
brane is  not  affected  in  the  same  manner  nor  on  all  the  same  points  of 
its  different  diameters.  The  transmission  of  movement  to  the  fenestra 
ovalis,  which  is  a  genuineinternal  tympanum,  is  modifiedby  it,  andthe 
attack  on  this  membrane  is  concentrated  on  different  points  of  its 
surface,  whence  arises  a  displacement  of  the  labyrinthine  lymph,  this 
also  taking  place  in  different  directions,  so  as  to  affect  in  a  predominat- 
ing manner,  either  the  different  parts  of  the  crista  acustica  (in  the  sac- 
cule), or,  more  especially,  the  different  semicircular  canals.  Thus  we 
obtain  particular  indications  with  regard  to  the  source  of  the  aerial 
wave,  and  therefore  of  the  sound  heard  (Bonnier). 

2.  Excitations  of  intrasomatic  origin. — But  the  semicircular  canals 
are  also  accessible  to  another  kind  of  excitation  independent  of  all 
pressure  or  any  modification  of  pressure  of  the  external  medium  (aerial 
or  liquid).     Goltz  maintained  that  changes  of  position  of  the  head  in- 

^  P.  BoNNiEB,  Le  vertige  (Bibliotheque  Charcot-Debove). 


Fig.  245. — Diagram  representing  ampulla  of 
a  semi-circular  canal  and  acoustic  crest. 
(M.  Duval). 

AM,  ampulla  ;  CR,  its  acoustic  crest  ;  CB,  basal 
cells  ;  CS,  cells  of  support  ;  cc,  cuticle  ;  ca,  acoustic 
cells  and  their  cilia  ;  N,  nerve  fibre  going  to  the 
acoustic  cells. 


AUDITORY  INNERVATION  609 

fluenced  the  distribution  of  the  Hquid  in  these  canals  and  became  the 
cause  of  the  sensations  by  which  equihbrium  is  regulated.  Breuer 
defined  this  conception  by  pointing  out  that  the  labyrinthine  lymph 
(endolymph),  by  virtue  of  its  iiiertia,  exerted  a  jriction  on  the  sensory 
wall  of  the  ampullae  when  the  head  was  moved.  Some  variations  of 
this  explanation  attribute  the  excitation  of  the  ampullary  nerves  to  a 
counter- pressure  (but  ^\athout  displacement  or  friction)  of  the  lymph 
against  the  wall  in  a  direction  contrary  to  the  displacement,  or  else  to 
some  irritation  of  an  unknown  nature,  but  probably  connected  with 
acceleration.  According  to  Breuer,  Mach,  Crum-Brown,  the  semi- 
circular canals  are  the  organ  of  sensations  of  acceleration. 

Relation  between  the  direction  of  the  movement  and  that  of  the  semi- 
circular canals. — Previously  to  all  these  explanations  Flourens  had 
demonstrated  (1824),  by  very  striking  experiments,  the  strict  connexion 
which  unites  the  semicircular  canals  to  the  co-ordination  of  movements, 
and  consequently  to  equilibrium.  Separate  section  of  each  of  the  canals 
produces  disorderly  movements,  in  the  direction  of  the  plane  of  the  muti- 
lated canal. 

Pierret,  Brown-Sequard  and  Bechterew  have  shown  that  these 
disorders  may  also  be  observed  in  lesions  of  the  labyrinthine  nerve. 

Cyon  does  not  consider  that  the  movements  of  the  Uquid  or  the  liquid 
itself  cause  stimulation  of  the  ampullae.  He  brings  forward  as  an 
objection  the  viscosity  of  this  liquid  in  a  tube  of  capillary  dimen- 
sions, and  the  fact  that  its  escape,  after  the  opening  of  the  labyrinth, 
does  not  produce  a  loss  of  equilibration.  The  locomotory  disturbances 
brought  about  in  the  experiments  of  Flourens  would  be  due  to  an  exci- 
tation, not  to  a  paralysis  (Loewenberg).  The  destruction  (though 
certainly  complete)  of  the  semicircular  canals  does  not  cause  these 
disorders  (Steiner),  this  being  in  favour  of  the  lesions  acting  as  an  ex- 
citant. At  any  rate,  lesions  of  the  cochlea  bringing  deafness  in  their 
train  do  not  disturb  the  equilibrium.  The  starting  point  of  convulsions 
is  in  lesions  of  the  ampullae  rather  than  in  that  of  the  canals,  that  is  to 
sa}^  in  the  locahty  which  contains  the  nerve  arborizations  (Lussana). 

Unconscious  sensations. — A  point  about  which  there  is  room  for 
insistence  is  that  impressions  and  sensations  having  this  origin  are  not 
conscious  (at  least  not  habitually  conscious),  but  are  connected  with 
reflex  acts  which,  by  being  exaggerated,  in  lesion  of  the  canals  become 
convulsive  (Loewenberg,  Laborde). 

3.  Link  between  the  muscular  tonus  and  the  motor  power. — The 
relation  between  the  semi-circular  canils  and  muscular  movement 
is  a  close  one,  and  displayed  in  a  very  evident  manner  to  all  observers. 

R.  Ewald  maintains  that  these  organs  are  the  starting-point  of  con- 

P.  R  K 


610  SPECIAL  INNERVATIONS 

tinuous  and  permanent  impulses,  reflected  by  the  nervous  system  on  to 
the  muscular  tissue  ;  so  much  so,  that  after  section  of  the  labyrinthine 
nerve  or  destruction  of  the  canals,  muscular  relaxation  is  immediately 
produced,  and  displayed  by  loss  of  tonicity,  and  inability  in  the  animal 
to  perform  energetic  movements.  In  fact,  the  ayiimal  jweserves  its 
muscular  energy,  hut  no  longer  knows  liow  to  emjjloy  it. 

H.  Girard  has,  it  is  true,  remarked  in  the  frog,  after  unilateral  section 
of  the  acoustic  nerve  and  destruction  of  the  labyrinth,  the  reflex  excit- 
ability of  the  corresponding  side  to  be  increased. 

This  connexion  of  the  labyrinthine  apparatus  with  motricity  is  also 
defined  in  the  experiments  of  Cyon,  who  shows  that  there  is  a  deter- 
minate relationship  between  the  excitation  of  each  canal  in  particular, 
and  the  movements  of  the  eyeballs.  And  these  relations  are  such  that 
the  movement  produced  (by  a  reflex  path)  corrects,  or  tends  to  correct, 
the  visual  illusion  which  arises  from  the  movement  provoked.  And  a 
relation  of  the  same  nature  would  also  exist  with  the  locomotor  muscles 
(Y.  Delage). 

4.  Analysis  of  the  perceptions  of  space. — Whatever  idea  may  be 
formed  with  regard  to  the  modality  and  nature  of  the  excitations  col- 
lected by  the  semicircular  canals,  the  relation  of  this  apparatus  to  the 
position  of  the  body  and  the  sense  of  space  cannot  be  denied.  The 
wave,  whatever  it  may  be,  which  reaches  the  three  canals  taken  as  a 
whole,  will  have  on  each  of  them,  by  reason  of  the  relative  arrangement 
of  their  planes  at  right  angles,  an  unequal  action  on  each  of  the  three, 
and  one  which  differs  according  to  its  own  direction.  The  idea  of  this 
direction  is  drawn  from  the  comparative  value  of  the  excitations  pro- 
duced on  each  of  the  three  canals.  The  movements  of  the  head  in 
different  directions,  changes  of  place  in  the  body  as  a  whole,  are  equally 
as  regards  the  different  canals  both  right  and  left,  the  origin  of  equal, 
unequal,  or  inverse  excitations,  which  give  us  information  with  regard 
to  changes  of  position  of  the  head  or  body,  and  also  concerning  the 
movement  of  the  latter,  and  any  acceleration  of  this  movement. 

By  the  muscular  sense,  or  that  which  has  been  more  correctly  called 
the  cinesthetic  impressions,  we  are  instructed  with  regard  to  the  relative 
displacements  of  our  limbs  and  their  segmentary  positions  ;  from  the 
sensations  produced  by  the  semicircular  canals  we  receive  information 
with  regard  to  changes  of  place  in  our  bodies  and  its  attitudes,  in  con- 
nexion with  the  surrounding  medium.  In  that  special  sense  which  has 
been  called  the  sense  of  space,  a  preponderating  position  is  taken  by 
the  apparatus  called  auditory,  and  it  owes  this  to  an  organ  distinct 
from  that  which  collects  sounds  ;  still  this  position  is  not  entirely 
exclusive.     Touch  procures  information  of  the  same  nature  with  regard 


AUDITORY  INNERVATION  611 

to  objects  in  immediate  contact  with  us.  Sight  furnishes  us  with  it  for 
distant  objects.  Between  these  two  senses  and  the  ear  the  difference 
is  that  locahzation  of  the  exciting  cause  is  in  the  latter  made  by  the 
sensorial  apparatus  itself,  and  not  by  an  apparatus  other  than  the 
sensorial.  The  retina  at  the  same  time  sees  and  locahzes  objects  {visual 
sense  of  sjmce)  ;  the  skin  gives  us  the  idea  of  contact  and  also  of  the 
position  of  bodies  [tactile  sense  of  space).  In  the  ear  the  cochlea  hears, 
and  the  semicircular  canals  localize  the  sound  heard  {auricular  sense 
of  space,  which  by  some  is  considered  as  the  only  sense  of  space). 

5.  Superposition  and  synthesis  of  notions  of  space  furnished  by  each 
sense. — Thus,  wherever  there  is  exteriorization  and  locahzation  of  the 
originating  cause  of  sensation,  there  is  an  idea  or  sensation  of  space. 
Each  sense,  in  different  degrees,  is  a  sense  of  space  ;  further,  each  sense 
duplicates  this  common  and  primordial  idea  of  specific  sensation  ;  that 
is  to  say,  one  which  is  irreducible  to  the  sensation  belonging  to  the 
other  senses.  It  is  by  their  sjMtial  element  that  these  ideas  are  super- 
pdsable.  It  is  by  the  superposition  of  these  ideas  that  we  identify  the 
objects  of  which  different  senses  display  to  us  the  various  qualities 
(Bonnier).  It  is  by  successive  identifications  that  we  pass  from  the 
sensation  to  the  idea,  and  the  vocal  or  graphic  sign  expressing  it, 
then  from  the  simple  to  the  general  idea,  from  the  concrete  to  the 
abstract. 

Objective  and  subjective  orientation. — The  perceptions  which  maintain  the 
sense  of  orientation  are  of  two  orders,  or  at  least  may  be  classed  under  two  head- 
ings. The  first  give  lis  information  concerning  the  situation  of  objects  and  their 
relations  with  us  and  with  each  other,  and  variations  in  these  relations,  that  is 
to  say,  their  movements  or  changes  of  position  ;  they  are  furnished  to  us  by 
those  senses  which,  like  sight,  touch,  and  even  hearing,being  open  to  the  external 
world,  receive  shocks  either  dii'cctly  or  indirectly  of  extrasomatic  origin,  and  which 
are  gradated,  as  indeed  are  these  objects  themselves  ;  this  is  objective  orientation. 
The  second  instruct  us  concerning  the  position  of  our  bodies  with  regard  to  these 
objects  and  to  changes  in  this  position  :  they  reach  us,  in  a  great  measure,  from 
an  apparatus  to  which  the,sense  of  hearing  is  as  it  were  annexed,  the  semicircular 
canals  and  the  utricule  which  are  arranged  so  as  to  collect  excitations  of  intra- 
somatic  origin  from  the  fact  of  the  movements,  or  only  from  the  attitude  of  oiu' 
body  :    this  is  subjective  orientation  (Bonnier). 

The  distinction  between  objective  and  subjective  is  here,  as  may  be  seen, 
drawn,  not  from  the  pliysical  or  psychical  nature  of  the  phenomena,  but  from 
the  anatomical  and  functional  difference  between  the  receptive  apparatus  of  the 
senses.  This  division,  however,  is  not  absolute,  since  the  labyrinth  itself  is  cap- 
able of  giving  us  information  with  regard  to  the  direction  of  the  shocks  coming 
to  it  from  external  objects,  and  hence  of  their  situation,  and,  on  the  other  hand, 
deep  tactile  sensibility  also  instrvicts  vis  concerning  the  relative  situation  of  oxir 
organs  and  limbs. 

The  labyrinthine  apparatus  is  constructed  so  as  to  furnish  us  with  a  faithful 
analysis  of  the  movements  (and  even  the  positions)  of  ovu'  body  with  regard  to 
the  three  dimensions  of  space.     But  these  three  dimensions  are  not  selected 

R  R* 


612  SPECIAL  INNERVATIONS 

arbitrarily.  Tliere  is  at  least  one  of  the  three,  the  vertical,  which  is  given  by 
weight,  and  which  represents  a  force  or  excitation  at  a  distance,  defining  the  posi- 
tion of  oiir  body  with  regard  to  the  earth  svipporting  us  ;  so  that  subjective 
orientation  is  itself,  as  it  were,  slightly  tinctiired  by  objective  orientation. 
Fundamentally,  objective  and  subjective  orientation  preside  over  each  other 
mutually,  as  do  action  and  reaction,  and  the  disturbance  of  one  may  bring  about 
that  of  the  other. 

Vertigo. — Vertigo  is  defined  by  Bonnier  as  being  a  disturbance  of  subjective 
orientation,  supervening  either  directly  or  indirectly.  Like  so  many  others,  the 
function  of  orientation  can  only  be  correctly  exercised  by  means  of  reciprocal 
links  between  sensibility  and  movement  ;  whence  it  follows  that  vertigo  includes 
both  sensory  and  motor  phenomena  which,  taken  separately,  would  not  be 
sufficient  to  characterize  it.  In  all  concerning  sensibility,  vertigo  may,  like 
orientation  itself,  be  either  conscious  or  unconscious.  However,  speaking 
clinically,  it  is  by  the  special  sensation,  sui  generis,  accompanying  it  that  it  is 
habitually  characterized  ;  whence  the  definition  of  Grainger  Stewart  accepted 
by  Weill :  vertigo  is  "  the  feeling  of  the  instability  of  our  position  in  space 
relative  to  surrounding  objects.  In  reality,  vertigo  may  exist  withovit  con- 
sciousness of  giddiness,  vmconscious  orientation  (the  most  usual)  being  capable 
of  disturbance  like  conscious  orientation  (more  exceptional). 

Forms  of  vertigo. — There  may  be  vertigo  from  want  of  perception  of  space 
(momentary  suspension  of  all  conscious  localization),  from  too  acute  perception 
of  space  (vertigo  of  heights,  agoraphobia),  from  illusion  of  space  (illusion  of 
position,  direction),  or  from  hallucination  of  space  (obsession  of  an  unreal  void,, 
or  unreal  movement  or  position).     (See  Bonnier,  Vertige,  Bibl.  Charcot-Dehove). 

Different  origins  of  vertigo. — The  sensorial  apparatus  which,  like  those  of  sight, 
of  touch,  and  especially  the  semicircular  canals,  furnish  the  most  important 
information  for  the  guidance  of  the  function  of  orientation,  may  by  the  disturb- 
ance, and  therefore  the  discordance  of  their  operations,  become  the  exciting 
cause  of  vertigo. 

Optical  vertigo. — Weill  enumerates  a  series  of  circumstances  which  may  produce 
op)tical  vertigo,  principally,  however,  in  neurotic  subjects  :  abrupt  transition 
from  darkness  to  light  or  conversely  (Purkinje),  sight  of  numerous  colours  riuming 
into  each  other,  or  of  material  ornamented  with  lozenges  giving  tlie  illusion  of 
movement,  passing  in  front  of  a  railing,  sight  of  running  water,  or  of  a  rotatory 
body,  etc.,  etc. 

Labyrinthine  vertigo  or  that  of  Meniere. — Meniere  was  the  fii'st  to  observe  a 
very  well  characterized  form  of  vertigo,  having  as  a  starting-point  alterations  in 
the  internal  ear  and  especially  in  the  labyrinth.  It  must  be  noted  that  people 
born  deaf  are  but  little  subject  to  vertigo  or  to  sea-sickness. 

Vertigo  of  tactile  origin  ;  mixed  vertigo. — The  sense  of  touch  takes  part  in  many 
ways  in  orientation  and  equilibration.  Weill  gives  proof  of  the  existence  of  a 
vertigo  of  the  muscular  sense.  An  excitation  which  has  its  starting-point  in  a 
single  sense,  often  in  the  restricted  locality  of  a  single  nerve  trunk,  may  spread 
by  being  propagated  to  the  neighboviring  sensory  or  sensorial  nuclei  (nuclei  of 
the  vestibular  nerve)  ;  whence  arise  many  forms  of  vertigo  having  a  starting- 
point  in  the  stomach,  the  nasal  mucous  membrane,  the  pharynx,  the  heart,  the 
ureter,  etc.,  and  whence  also  are  produced  many  external  and  internal  motor 
reactions  (palpitations,  nausea,  etc.)  accompanying  vertigo.  Finally,  the  ex- 
citations may  have  many  origins,  as  in  the  naupathia  of  sea-sickness  (see  Weill^ 
Des  vertiges,  these  d'ag.  de  Paris,  1886). 

Not  only  may  abnormal  excitation  have  varied  and  nmnerous  sensorial  origins, 
but  as  regards  the  same  sense  functional  alteration  may  have  a  varied  place  in 
the  cycle,  and  affect  the  receptive  apparatus,  the  sensorial  conductors,  the  bulbo- 


AUDITORY    INXERVATION  613 

medullary  nuclei,  the  cerebellum,  and  the  brain,  whence  so  manj-  kinds  of  vertigo, 
bulbar,  cerebellar,  cerebral,  etc. 


2.     Specific  sensation  or  tliat  of  auditory  tonality 

1.  Auditory  field. — We  have  an  auditory  just  as  we  have  a  visual 
field  ;  and  the  former,  instead  of  extending  in  front  of  us,  as  does  the 
latter,  is  situated  laterally,  in  the  form  of  an  extremely  spread-out 
cone,  whose  axis  is  located  in  the  prolongation  of  the  auditory  meatus, 
and  whose  base  is  external.  We  have  in  reality  two  auditory  fields, 
one  for  each  ear ;  but  whereas  the  visual  fields  of  both  eyes  are  super- 
posed so  as  to  form  but  one,  the  auditory  fields  are  diametrically 
opposed.  Nevertheless,  they  partially  overlap  so  as  to  fill  the  hiatus 
which  they  tend  to  leave  either  in  front  or  behind.  It  is  behind  that 
this  gap  is  most  obvious  ;  and  it  is  at  the  back  of  the  head  that  approach- 
ing deafness  at  first  shows  itself,  and  it  is  in  the  prolongation  of  the 
axis  of  the  auditory  duct  that  audition  persists  the  longest  (Gelle). 

This  orientation  in  an  opposite  direction  of  the  auditory  fields  of  the 
two  ears  gives  rise  to  conditions  which  are  special  to  binauricular  audi- 
tion and  renders  it  very  different  from  binocular  vision.  It  suppresses 
certain  of  the  advantages  of  the  latter  ;  but  at  the  same  time  creates 
new  ones.  From  the  fact  of  the  lateralization  of  a  sound,  in  the 
exteriorization  made  for  us  by  it,  we  arrive  at  some  idea  of  its  origin 
and  of  its  localization  in  space.  We  guide  ourselves  by  this  indication ; 
either  by  turning  the  head  and  the  ear  distinctly  to  face  the  sound, 
if  we  wish  to  hear  it  better ;  or,  on  the  contrary,  by  turning  the  head 
and  the  eyes  in  its  direction,  if  we  wish  to  see  the  original  cause  of  it ; 
this  is  an  act  of  voluntary  motor,  instinctive  orientation  (Gelle). 
This  movement  may  be  compared  to  that  made  by  the  eyes  in  order 
to  locate  the  image  of  the  objects  on  the  central  part  of  the  retina. 
But,  whatever  be  the  direction  of  the  head  and  the  ear,  and  without 
the  necessity  of  any  change  in  their  position,  we  have  a  means  of 
recognizing  the  direction  of  the   aerial  wave  which  reaches  us. 

The  apparatus  which  analyses  the  direction  of  the  exciting  wave  is 
situated  in  the  internal  ear,  the  labyrinth,  and  especially  in  the  semi- 
circular canals  (Bonnier).  We  have  seen  above  how  this  analysis  is 
performed  and  how  distinct  is  the  apparatus  which  analyses  the  direc- 
tion of  the  wave  from  that  which  analyses  tonality. 

Binauricular  audition. — Consciousness  is  one  and  alone  ;  it  is  in 
every  case  the  characteristic  of  our  unity,  that  is  to  say,  of  our  being. 
The  excitations  penetrating  our  nervous  system,  in  proportion  as  they 
reach  its  depths,  are  synthetized  into  a  sensory    phenomenon  which 


614  SPECIAL  INNERVATIONS 

does  not  allow  of  their  component  elements  being  longer  distinguished, 
or,  at  least,  which  establishes  no  distinction  except  between  their 
principal  groups,  and  that  generally  only  on  the  condition  of  an  effort 
of  the  attention  seeking  for  them  in  the  field  of  consciousness.  Sounds, 
even  when  they  strike  unequally  on  our  two  ears,  give  us  but  a  single 
perception.  This  inequality  in  the  intensity  of  the  impression  may, 
nevertheless,  be  in  some  degree  perceptible,  as  it  is  pointed  out  by  a 
motor  phenomenon  of  orientation ;  only  this  perception  is  not  usually 
of  a  distinct  nature,  but  is  obscure,  resembling  that  which  regulates 
reflex  or  automatic  acts. 

2.  Fusion  of  excitations  into  the  sonorous  sensation, — When  vibra- 
tions with  a  long  interval  between  them  strike  the  ear,  they  act  as 
isolated  excitations,  and  can  be  separately  distinguished.  When  these 
vibrations  attain  a  frequency  of  sixteen  shocks  or  oscillations,  we  can 
still  distinguish  them,  but  can  no  longer  recognize  an  interval  of  silence 
between  them. 

Thus  the  nervous  system  possesses  the  power  of  associating  impulses 
in  time,  just  as  it  has  the  power  of  associating  the  simultaneous  stimula- 
tions of  the  two  labyrinths  and  of  the  component  elements  of  each  of 
them.  In  proportion  as  the  frequency  augments,  the  fusion  becomes 
more  complete  :    sensation  is  continuous. 

3.  Damping  of  the  vibrations  special  to  the  ear. — A  movement 
applied  to  a  body,  should  the  latter  be  of  an  elastic  nature,  tends  to 
communicate  to  it  a  vibration  which  persists  after  the  shock,  even  if 
this  be  instantaneous  and  not  reiDcated.  This  secondary  vibration, 
were  it  permitted  to  exist,  would  absolutely  falsify  the  information 
which  the  sense  of  hearing  supplies.'  Special,  but  so  far  undetermined 
conditions,  certainly  exist  in  the  labyrinth,  whose  effect  is  to  damp 
this  secondary  vibration,  so  that  only  the  primary  vibration  is  utilized 
for  the  stimulation  of  the  auditory  apparatus.  The  viscous  nature 
of  the  liquid  which  is  displaced  in  tubes  of  capillary  dimensions  is  a 
circumstance  which  may  help  to  explain  this  phenomenon  of  the  damp- 
ing of  the  vibrations  (Bonnier). 

Thus  conditions  exist  at  the  origin  of  the  nervous  cycle  in  the  organ 
which  receives  the  impulse  which  cause  the  movement  received  to 
possess  exactly,  or  all  events  sensibly,  the  same  value,  not  only  with 
regard  to  intensity,  but  also  as  concerns  duration,  as  the  external  move- 
ment communicated  to  it.  But  in  the  nervous  system  itself  the  excita- 
tion (transformed  into  a  nervous  wave)  has  a  far  more  prolonged  echo, 
whence  arises  the  fusion  of  impulses  succeeding  each  other  with  a 
rhythm  of  rather  more  than  ten  to  the  second,  and  the  unity  or 
continuity  in  time  of  the  resulting  sensation. 


AUDITORY    INNERVATION  615 

If  a  sound  is  too  short,  it  is  not  (other  things  being  equal)  perceived 
below  a  certain  duration  (Gelle). 

4.  Rate  of  development  of  the  sensation. — The  excitation,  in  order 
to  terminate  in  the  psychical  phenomenon  of  sensation,  must  be  de- 
veloped in  the  nervous  system.  This  development,  which  implies 
phenomena  of  succession  and  association,  which  are  at  the  same  time 
both  numerous  and  complicated,  requires  a  certain  time  for  its  elabor- 
ation.    Methods  have  been  devised  to  determine  this  period  of  time. 

The  method  is  a  general  one.  The  shortest  interval  which  elapses 
between  the  commencement  of  an  auditory  impulse  and  the  motor 
reaction  which  answers  to  this  impulse,  is  measured.  Beaunis  estimates 
this  interval  as  being  106  to  159  thousandths  of  a  second  or,  on  an 
average,  and  in  round  numbers,  150  thousandths  of  a  second.  It  may 
through  practice  fall  to  100,  say  a  tenth  of  a  second.  This  delay  is 
certainly  longer  than  the  time  required  for  transmission  along  the  course 
of  a  single  nervous  conductor.  The  impulse  is  delayed  by  the  multiple 
and  graduated  transformations  which  take  place  in  the  grey  matter, 
and  especially  by  the  cerebral  transformations,  an  attempt  having 
been  made  to  separate  these  from  other  superposed  transformations 
which  are  sufficiently  well  known.  According  to  Richet,  these  cerebral 
transformations  Avould  require  a  half-tenth  of  a  second. 

When  sounds  possessing  different  characteristics  (hke  the  articulated  sounds 
of  speech)  succeed  each  other,  a  certain  interval  between  them  becomes  necessary 
in  order  that  they  may  be  distinctly  perceived,  that  is  to  say,  that  their  characters 
may  be  recognized.  Richet,  according  to  his  own  personal  experience,  estimates 
the  rate  of  articulation  of  syllables,  either  spoken  or  thought,  at  ten  in  a  second. 
It  is  this  very  rate  which  limits  the  perception  of  the  words  which  we  hear  pro- 
nounced. The  delay  is  of  a  psychical  nature.  It  is  also  necessary  that  our 
attention  should  be  awake,  for  a  sound  or  a  noise  which  takes  us  by  surprise 
undergoes  a  much  greater  delay  before  arriving  in  our  consciousness.  This 
latter,  however,  once  warned,  rapidly  discerns  it  should  it  be  reproduced. 

B.     TRANSMISSION  FROM  THE  EAR  TO  THE  CEREBRAL  CORTEX 

The  acoustic  nerve,  or  that  of  the  eighth  pair,  is  formed  by  the  union 
of  two  nerves,  each  arising  from  a  special  organ  adapted  to  the  reception 
of  certain  stimulations  ;  these  two  nerves  are  :  (1)  the  cochlear  nerve, 
which  is  stimulated  by  the  displacement  of  a  liquid  filling  the  cochlea, 
these  displacements  being  due  to  the  pressure  exercised  by  the  vibra- 
tions of  air  or  of  sonorous  bodies  ;  (2)  the  vestibular  nerve,  which  is  also 
stimulated  by  the  displacements  of  a  liquid  filling  the  semicircular 
canals,  which  displacements  are  in  this  case  due.  not  merely  to  the 
aerial  waves  arriving  from  the  exterior,  but  also,  and  more  especially, 
to  changes  of  position  of  the  head  or  of  the  body. 

R  R** 


616 


SPECIAL  INNERVATIONS 


Post.  N. 


N.  of  Deiters 


.»-•  Lat.  ac.  tub. 


Ant.  N. 


The  cochlear  nerve  traverses,  in  the  same  way  as  the  posterior  roots, 
a  ganghon  situated  at  the  base  of  the  lamina  spiralis,  and  is,  like  the 
latter,  twisted  {spiral  ganglion,  or  ganglion  of  Corti). 

The  vestibular  nerve  also  passes  through  a  ganglion  at  the  bottom 
of  the  internal  auditory  meatus  {vestibular  ganglion,  or  that  of  Scarpa). 

These  two  nerves  are 
not  entirely  independ- 
ent, for  the  cochlear 
nerve  gives  off  a  small 
branch  to  the  saccule 
and  to  the  ampulla  of 
the  inferior  semicircular 
canal  ;  the  ganglion 
of  this  small  branch 
lies  at  the  bottom  of 
the  internal  auditory 
meatus. 


Semi-circ.  can. 

G.  of  Scarpa 

Coch'ea 

Spiral  G.  {Corti) 
the    acoustic 


JJ^ 


Fig.  246.— Origin 


and    termination 
nerve. 


vestib.  N.  Vestibular    nerve. — The 

vestibular  nerve  has,  like 
the  posterior  roots,  two 
radicular  branches  ;  the 
inferior  branch  terminates 
in  a  grey  mass  situated  im- 
mediately above  the 
nucleus  of  Burdach,  of 
which  it  is  a  kind  of  pro- 
longation. The  inferior 
radicular  branch  of  the 
vestibular  nerve  is  then  in 
reality  eqmvalent  to  the 
superior  branch  of  the  sensory  nerves  of  the  spinal  cord,  and  this  remark 
applies  to  the  inferior  radicular  branch  of  the  glosso-pharyngeal,  a  sensorial  and 
sensory  nerve,  and  also  to  that  of  the  trigeminal  and  of  the  vagus,  sensory  nerves. 
The  superior  radicular  branch  (generally  called  superior  root)  of  the  vestibular 
nerve  comes  in  contact  in  a  very  restricted  space  with  three  nuclei,  called  the 
internal  dorsalnucleiis,  the  external  dorsal  nucleus  (or  that  of  Deiters),  and  the  nticleus 
of  Bechterew.  From  these  different  nuclei  fibres,  called  cerebellar,  arise,  which, 
with  the  help  of  the  inferior  cerebellar  peduncle,  reach  the  cerebellum  either  with 
or  without  decussation,  where  they  terminate  in  the  nucleus  of  the  roof,  the 
nucleus  glohosus,  and  the  nucleus  emboliformis.  These  fibres  are  obviously  equiva- 
lent to  those  which,  in  the  tactile  system,  form  the  cerebellar  tract  of  the  spinal 
cord.  Other  fibres,  emanating  from  the  primary  nuclei  (internal  and  external 
dorsal,  and  of  Bechterew),  and  perhaps  also  from  the  nuclevis  of  the  inferior  root, 
pass  through  the  reticular  formation,  and  after  enlarging  the  fillet  (riband  of 
Reil)  finally  reach  their  destination  in  the  cerebral  cortex. 

Thus  the  impulse,  on  leaving  these  nuclei,  follows  j^aths  which  convey  it  either 
to  the  brain,  or  to  the  cerebellimi  :  further,  there  are  some  which  from  these 
same  nuclei,  and  especially  from  the  external  dorsal  nucleus,  may  convey  it  to 


AUDITORY    INNERVATION 


617 


the  nucleus  of  origin  of  the  external  oculo-motor  nerve  ;    so  that  to  the  cerebral 
and  cerebellar  paths,  reflex  paths  must  also  be  added. 

Cochlear  nerve. — From  the  locality  where  the  cochlear  nerve  comes  in  contact 
with  the  medulla  oblongata  by  its  lateral  portion,  up  to  the  cortex,  the  acoustic 
cochlear  paths  traverse  or  skirt  along  a  series  of  gi'ey  nuclei  which  are  :  (a)  the 
anterior  nucleus,  and  the  acoustic  tubercle  (quite  at  the  entrance),  (b)  the  nuclei 
of  the  trapezoid  body  (either  of  the  same,  or  of  the  opposite  side  after  decussation). 


Corp.  quad. 


int.  gen.  body 


"-  Dir.  T. 


~  .\nt.  ac.  N 


._  CoeU.  y. 


Fig.  247. — Diagram  of  the  acoustic  tract  (central  acoustic  path  of  the  cochlear  nerve, 

Charpy). 


(c)  the  lateral  nucleus  of  the  fillet  {riband  of  Reil),  (d)  the  corpora  quadrigemina 
(principally  the  posterior),  (e)  the  internal  geniculate  body,  after  which  the  fibres 
reach  the  cortex  of  the  temjaoral  lobe. 

The  fibres  which  either  pass  through  or  stoj^  in  these  different  ganglia  are  some- 
times superficial,  like  the  acoustic  strife,  and  the  posterior  arms  of  the  corpora 
quadrigemina,  and  sometimes  deep,  like  the  traiaezoid  body  or  the  fillet  (riband 
of  Reil). 

We  may  add  that  the  acoustic  paths  are  also  connected  with  the  optic  thalamus. 
This  important  organ  is,  in  a  manner,  like  the  cortex  itself,  distributed  between 
the  different  senses.     The  pulvinar  is  connected  with  vision  ;    between  the  pul- 


618 


SPECIAL  INNERVATIONS 


Dorsal  N. 


vinar  and  the  internal  nucleus  a  segment  is  situated  wliich  is  united   by  tracts 
to  the  temporal  lobe,  and  which  is  connected  with  audition. 

The  presence  in  the  course  of  the  auditory  paths  of  ganglionic  masses,  like  the 
above-mentioned  segment  of  the  thalamus,  the  posterior  corpus  quadrigeminum, 
the  internal  geniculate  body,  all  having  such  a  striking  resemblance  to  the  ganglia 
passed  through  by  the  optic  tracts  (pulvinar,  anterior  corpus  quadrigeminum, 
external  geniculate  body),  establishes  an  obvious  homology  between  the  two 
sensorial  systems  and  tlieii*  principal  relays. 

The  functional  significance  of  these  different  nuclei  would  be  of  the  highest 
interest,  were  it  possible  to  ascertain  it  correctly,  either  by  experiment,  or  even 
by  comparison  with  the  similar  nuclei  of  the  other  senses.     On  this  point  positive 

data  are  almost  entirely 
wanting.  At  the  same 
time  it  may  be  observed 
that  amongst  these  grey 
masses  there  are  some 
which,  like  the  corpora 
quadrigemina,  are  e  s  - 
pecially  localities  for 
reflexion  of  the  impulses  : 
the  anterior  c  o  r  p  o  r  a 
quadrigemina  reflect  the 
visual,  the  posterior  the 
auditory  impulses.  The 
other  grey  masses  are  jier- 
haps  not  entii-ely  de- 
prived of  this  power  of 
reflexion,  but  instead  of 
bringing  back  the  im- 
pulse towards  its  start- 
ing-point, they  seem 
rather  to  deflect  it  in  the 
direction  of  the  deep 
paths  leading  to  the  cortex. 
As    they    pass    on,  they 


..Cereb.  pel. 


Ac.  tub. 


Ant.  ac.  N. 


..  CochJ.  X. 


Vest.  N. 


Sup.  ulive 


Pyr.  T. 


Keil 


Fig.   248. — The  acoustic  stri*. 


The  striae  and  the  trapezoid  body  in  blue.     Transverse 
section  of  the  pons.     Diagrammatic  (Charpy). 


associate  the  elementary  impulses,  and  thus  in  a  way  sketch  out  the  work 
of  synthesis  from  which  arises  the  specific  sensation  of  audition,  when  these 
impulses,  following  a  determinate  order  and  connexion,  shall  arrive  in  the  cortex. 
So  far  as  can  be  ascertained,  the  general  plan  of  these  connexions  between 
fibres  is  the  same  here  as  in  the  other  senses.  It  is  in  j^rinciple  maintained  that 
in  these  fibrillary  paths  going  from  the  ear  to  the  brain,  there  is  at  least  one  break, 
and  therefore  at  least  two  neurons  transmitting  the  impulse.  These  breaks  do 
not  all  occur  in  the  same  locality,  but  are  graduated  in  stages  on  the  different 
nuclei  which  succeed  each  other  along  the  nerve  path  ;  hence  each  nucleus  pi"e- 
sents  terminal  fibres  and  fibres  of  passage.  Nevertheless,  the  fibres  of  passage 
emit  collaterals  which  have  practically  the  value  of  terminal  fibres,  so  that  the 
same  neviron  coming  from  the  periphery  distributes  impulses  to  several  nuclei. 
The  neurons  which,  from  these  nuclei,  proceed  to  the  cortex  are  in  general  much 
more  numerous  than  those  coming  from  the  periphery  to  them  Further,  be- 
tween one  nucleus  and  another,  as  between  the  elements  of  the  same  nucleus, 
there  are  longer  or  shorter  neurons  called  neurons  of  association,  whose  part  it  is 
to  solidarize  and  harmonize  the  elementary  actions  of  the  neurons  conveying  the 
impulses  to  these  grey  masses.  Finally,  in  a  certain  number  of  these  masses  the 
impulse  has  to  make  a  choice  between  two  directions  which  are  not  merely  dif- 


AUDITORY    INNERVATION 


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620 


SPECIAL  INNERVATIONS 


MUTUAL  RELATIONSHIP  OF  THE  PRINCIPAL  PRIMARY  AND 
SECONDARY  NUCLEI  (after  Bonnier). 


Origins. 


Terminations. 


Anterior  Nucleus  (or  inferior) 


Globular  Nucleus 


Internal  nucleus  of  the  same  side. 

Superior  olive  of  the  same  side. 

Superior  olive  of  the  opposite  side. 

Corpus  quadrigeniinum  of  the  opposite  side  (by 
the  trapezoid  body). 

— Thence  to  the  postero-basilar  nucleus  of  the 
1        optic  thalamus. 
I    — iTlience  also  to  the  interna]  geniculate  body, 
\       and  by  it  to  the  temporal  lobes. 

I 

j'  Anterior  nucleus  of  the  same  side, 

r  -vT  Superior  olive  of  the  same  side. 

Internal  Nucleus -^  ^^^^^^^,^  ^f  the  roof  of  the  same  side. 

Nucleus  of  the  roof  of  the  opposite  side. 

Cortex  of  the  superior  vermis. 

Cortex  of  the  superior  vermis. 
Red  nucleus  of  Stilling. 

— Thence  to  the  tactile  area  of  the  cerebral 
cortex. 

Cerebellum. 

Fundamental  tract  of  the  lateral  columns  of 
the  spinal  cord. 

Anterior  nucleus  of  the  same  side. 
Anterior  nucleus  of  the  opposite  side. 
Internal  nucleus  of  the  same  side. 
Nucleus  of  the  roof  of  the  same  side. 
Oculo-motor  and  facial  nuclei. 
Corpora  c^uadrigemina. 

— Thence  course  towards  the  optic  layer  of  the 
cerebral  cortex. 

Temporal  lobes. 

Reunited  to  that  of  the  opposite  side  by  the 
commissure  of  Gudden. 


Nucleus  of  the  Roof 


Nucleus   of   Deiters    (or   ex- 
ternal) and  of  Bechterew 


Superior  Olives 


Internal  Geniculate  Body 
(receives  the  fibres  of  the 
anterior  nucleus) 


ferent  but  opposed  ;  it  may,  as  has  just  been  observed,  continue  its  progress  to- 
wards the  cortex,  but  it  may  also  return  by  paths  which,  for  this  reason,  have 
been  described  as  refle:x.  This  retrograde  course  does  not  always  and  necessarily 
conduct  the  impulse  to  the  muscles,  but  sometimes  causes  it  to  fall  into  nervous 
organs,  where  it  finds  an  employment  which  is  not  clearly  defined. 

Held,  who  has  studied  the  auditory  (cochlear)  nerve  very  thoroughly,  divides 
the  succession  of  its  constituent  elements  into  four  distinct  orders,  which  he  calls 
systems.  The  first  order  is  made  up  of  those  radicular  fibres  which  proceed  to 
the  anterior  acoustic  nucleus  and  the  acoustic  tubercle,  but  certain  of  which  also 
ascend  in  the  superior  olives,  and  some  in  the  grey  masses  situated  still  higher. 
The  fibres  of  the  second  order  follow  the  same  route  as  the  preceding  ones,  either 
by  starting  from  their  strictly  terminal  arborizations,  or  from  the  collaterals 
along  which  they  graduate  in  the  nuclei,  which  they  traverse  without  being  totally 
exhausted  therein.  They  arise  then  in  the  anterior  nucleus  and  the  acoustic 
tubercle,  in  the  olivary  bodies  of  the  medulla  oblongata,  and  in  the  trapezoid 
bodies,  and  in  the  nucleus  of  the  lateral  fillet  ;  some  amongst  the  number  go  as 
far  as  the  cortex  (genuine  fibres  of  projection  of  the  second  order)  ;    many  pass 


AUDITORY  INNERVATION 


621 


from  one  nucleus  to  another  in  a  centripetal  direction  (inter -nuclear  fibres  of 
association)  ;  an  important  portion  terminates  in  the  corpora  quadrigemina, 
and  especially  in  the  posterior  ;  some  of  them  become  involved  in  the  superior 
cerebellar  peduncle. 


4  c.  tub 


Coch. 
nerve 


Fig.  249. — Diagrammatic  representation  of  the  auditory  system  ;  cochlear  or  auditory 
system  properly  so  called  in  blue  ;  vestibular  system  or  that  of  orientation  in  red 
(copied  from  P.  Bonnier). 

Ill  to  X,  nuclei  of  cranial  pairs  marked  according  to  their  conventional  numbers. 

The  two  other  systems,  that  of  the  third  and  that  of  the  fourth  order  are,  with 
regard  to  the  preceding  ones,  reciu-rent  systems  :  they  convey  the  impulse  back 
in  the  direction  of  the  perif)hery  instead  of  involving  it  in  the  depth  of  the  central 
masses.     In  the  mxmbering  of  the  systems  having  here  as  a  basis  the  progress  of 


622  SPECIAL  INNERVATIONS 

the  impulse  in  the  nervous  cycle,  the  fibres  of  the  third  order  will  be  found  to  be 
practically  repeated,  but  with  an  orientation  opposite  to  their  conduction  ;  those 
of  the  second  order  follow  Held's  classification.^  They  redescend  either  from 
the  cortex  or  from  the  corpora  quadrigemina,  and  other  deep  nuclei,  to  the  so- 
called  primary  nuclei  of  the  auditory  nerve,  and,  thanks  to  their  different  lengths, 
and  also  to  the  presence  of  collaterals  given  off  on  their  progress,  they  are  distri- 
buted in  gradation  over  a  certain  number  of  these  nuclei,  but  without  going 
beyond  the  lowest  amongst  them.  Amongst  these  fibres  some  mvist  be  included 
which  form  part  of  tlie  longitudinal  bandelette  or  posterior  longitudinal  bvindle, 
whose  origins  are  situated  in  the  corpora  quadrigemina  and  whose  collaterals  are 
distributed  to  the  bulbar  nuclei  (oculo-motor)  and  whose  terminals  reach  the 
anterior  cornea  of  the  spinal  cord. 

The  fibres  of  the  fourth  order  are  motor  elements  arising  from  the  bulbar  nuclei 
(oculo-motor,  facial)  and  superior  medullary  (nerves  of  the  rotatory  muscles  of 
the  head  and  the  neck). 

C.     AUDITORY    CORTICAL    AREA 

Cortical  localization. — The  sensorial  area  of  audition  is  localized  in 
the  'posterior  portio7i  of  the  first  teJiiporal  convolution.  Some  authors 
consider  that  it  also  extends  to  the  posterior  part  of  the  second  temporal 
convolution. 

Partial  decussation. — Each  acoustic  nerve  is  connected  with  the  two 
auditory  areas.  Complete  deafness  then  (cortical)  will  only  supervene 
when  the  convolutions  above  mentioned  are  destroyed  on  both  sides. 
This  arrangement  obviously  recalls  that  of  the  optic  tracts  as  regards 
the  retina.  Yet  nothing  is  known  concerning  the  internal  ear  which 
recalls  the  mode  of  connexion  of  the  optic  nerve  with  the  two  right 
and  left  halves  of  the  retina,  and  the  laws  regulating  the  distribution 
or  the  mixture  in  each  cochlea  of  the  auditory  fibres  in  connexion  with 
the  two  hemispheres  are  also  unknown. 

The  localization  of  the  sensorial  auditory  area  in  the  temporal  lobe 
is  practically  based  on  the  same  kind  of  proof  as  are  the  other  analogous 
localizations,  namely  :  loss  of  hearing,  in  the  case  of  destruction  (bi- 
lateral) of  the  above-mentioned  cortical  area  [clinical  observations  in 

1  It  may  here  be  well  to  remember  that  the  classifications  of  the  different  authors 
although  based  on  the  same  anatomical  and  experimental  facts,  differ  as  regards  the 
numbers  given  to  the  diverse  orders  or  systems.  All  maintain,  in  principle,  that  there 
are  four  orders  of  fibres  of  projection  which  are  divided  on  the  one  hand  into  two  parallel 
groups,  and  on  the  other  hand  into  two  superposed  groups  according  to  the  direction 
of  the  break  which  separates  them.  An  imaginary  surface  passing  through  the  pari- 
phery  and  the  cerebral  cortex  is  supposed  to  separate  the  sensory  and  motor,  or  centri- 
petal and  centrifugal,  or  afferent  and  efferent  elements  ;  another  imaginary  surface 
passing  through  the  grey  axis  is  supposed  to  separate  the  neurons,  the  peripheral  from 
the  deep,  and  the  inferior  from  the  superior.  Speaking  generally,  the  peripheral  or 
inferior  neurons  proceeding  from  the  periphery  to  the  grey  axis,  or  conversely,  are 
called  fibres  of  projection  of  the  first  order,  and  those  going  from  the  grey  axis  to  the 
brain,  or  conversely,  fibres  of  projection  of  the  second  order,  whatever  be  the  direction 
of  the  conduction.  But  other  authors  have  inverted  these  numbers.  If  the  impulse 
be  followed  in  its  cyclic  progress,  the  classification  of  Held  must  be  admitted.  On 
the  other  hand,  it  must  not  be  forgotten  that,  in  addition  to  fibres  of  projection,  there 
are   a  large  number  of  fibres  of  association  of  all  lengths. 


AUDITORY    INNERVATION  623 

man  (Wernicke,  Friedlander  and  Naunyn),  experimental  destruction 
in  animals  (Munck,  Luciani  and  Sepilli]  ;  atrophy  of  the  sj^stem,  as  a 
result  of  its  permanent  loss  of  function  ;  degeneration  of  its  paths  of 
conduction,  as  a  result  of  the  destruction  of  its  origins  or  terminations  ; 
finally,  embryological  development  of  these  paths,  studied  thanks  to 
the  more  or  less  early  myelination  of  certain  bundles  which  this  myelin- 
ation  renders  more  obvious  in  the  midst  of  others. 

The  deep  situation  of  the  internal  ear  does  not  allow  of  the  per- 
formance with  the  same  facility  of  destructive  operations  comparable 
to  the  enucleation  of  the  ball  of  the  eye  ;  nevertheless,  section  (uni- 
lateral or  even  bilateral)  of  the  auditory  nerve  inside  the  skull  can  be 
performed. 

On  the  other  hand,  the  auditory  paths  may  be  attacked  through 
the  cortex.  Destruction  of  the  first  temporal  convolution  brings  about 
a  secondary  degeneration  w^hich  may  be  followed  into  two  distinct 
tracts,  terminating  in  the  internal  geniculate  body  passing  through  the 
internal  capsule,  which  they  traverse  perpendicularly  to  the  general 
direction  of  its  fibres.  The  internal  geniculate  body  is  itself  degener- 
ated ;  it  has  not  been  possible  to  follow  the  alteration  further 
(Monakow). 

These  tracts  are,  in  the  infant  of  two  months,  myehnated  before  those 
surrounding  them  in  the  same  locality  ;  they  may  be  seen  starting 
from  the  internal  geniculate  body,  to  terminate  (while  becoming  en- 
larged deep  down  and  a  little  below  the  fissure  of  Sylvius)  in  two  trans- 
verse gyri,  which  lose  themselves  in  the  first  temporal ;  they  are  the 
portion  of  the  corona  radiata  which  belongs  to  the  geniculate  body, 
and  attaches  it  to  the  cortex.  The  cochlear  nerve  is  not  mj^elinated 
till  after  birth  ;  it  is,  amongst  all  the  sensory  nerves,  the  last  to  be 
myelinated  (Flechsig). 

In  individuals  affected  with  congenital  deafness  (deaf  mutes),  these 
convolutions  have  been  found  atrophied. 

Physical  deafness  ;  psychical  deafness. — An  individual  who,  from  any 
cause  whatever,  has  lost  singly  but  completely  the  apparatus  receptive 
of  sonorous  stimuli  is  deaf.  His  deafness  is  of  a  physical  nature.  It 
abolishes  for  ever  the  physical  conditions  necessary  for  the  production 
of  auditory  sensation.  But  he  retains  in  his  brain  anterior  auditory 
images  ;  can  invoke  them  at  will,  mutually  associate  them  and  repre- 
sent to  himself  noises,  sounds,  words,  phrases,  and  ideas  corresponding 
to  them.  He  is  not  psychically  deaf,  and  he  still  regulates  a  great 
number  of  his  actions,  according  to  auditory  representations  arising 
in  him  by  the  association  of  auditory  impulses  w^hich  have  reached 
him  previously. 


624  SPECIAL  INNERVATIONS 

An  individual  who  has  singly  but  completely  lost  the  posterior  portion 
of  the  second  temporal  convolution,  and  also  certain  neighbouring 
regions  (inferior  operculum  of  the  fissure  of  Sylvius,  portion  of  the 
second  temporal  convolution)  is  not  physically  deaf ;  he  continues 
to  receive  sonorous  impressions  and  reacts  to  them  by  a  great  number 
of  complex  acts  whose  mechanism  is  instinctive  or  automatic,  and 
especially  of  a  defensive  nature  ;  but  this  individual  is  psychically 
deaf,  and  this  psychical  deafness  allows  of  variations  in  severity,  which 
also  resemble  those  of  the  corresponding  blindness,  in  cases  of  destruc- 
tion of  the  occipital  lobe. 

a.  Cortical  deafness. — Should  the  cerebral  cortex  be  attacked  sym- 
metrically in  the  aforesaid  regions,  the  psychical  deafness  is  total  ; 
there  no  longer  exists,  for  this  individual,  distinct  auditory  sensation 
properly  so  called.  At  first  sight  he  is  not  to  be  distinguished  from  an 
ordinary  deaf  person  who  has  lost  the  power  of  hearing  from  disease 
of  the  ear,  because  in  ordinary  language  the  term  audition  merely 
designates  the  specific  sensation  of  tonality,  which  is  a  cortical  condition^ 
and  which  he  has  lost  for  ever.  But  he  has,  nevertheless,  retained 
reflexes  of  great  importance  ;  and  the  idea  of  sj)ace,  which  is  of  laby- 
rinthine origin,  and  which  is  analysed  in  the  sub-cortical  systems,  is 
preserved,  since  he  has  no  vertigo. 

b.  Deafness,  properly  called  psychical. — The  lesion  may  be  of  such  a 
nature  that  the  sonorous  sensation  or  that  of  tonality  subsists  in  a 
distinct  state,  but  it  goes  for  nothing.  The  individual  who  perceives 
the  sonorous  sensation  does  not  recognize  it,  that  is  to  say,  he  does  not 
recognize  the  object  which  has  furnished  him  with  the  sensation.  The 
sound  of  a  clock  no  longer  recalls  to  him  the  object  clock.  He  is  brought 
back  by  his  lesion  to  the  period  of  his  earliest  auditory  education,  with 
this  aggravating  circumstance  :  that  he  has  lost  the  power  he  previ- 
ously possessed  of  associating  his  sensations  in  time,  either  as  regards 
their  succession  or  their  contemporaneous  occurrence. 

c.  Verhal  deafness  or  that  for  words. — A  cortical  lesion  may  have 
still  more  restricted  consequences.  It  may  allow  of  the  subsistence 
of  the  sensation  of  sound  and  of  recognition  of  the  object,  while  sup- 
pressing the  recognition  of  the  ivord,  that  is  to  say,  the  appreciation 
of  its  conventional  signification.  The  verbal  sound  "  clock,"  will 
arouse  no  idea  of  the  object  clock.  And  this  alteration  itself  is  sus- 
ceptible of  degrees,  since,  in  individuals  speaking  several  languages, 
it  may  suppress  one  or  several  of  these  while  allowing  of  the  persistence 
of  one,  namely  :  that  which  was  learnt  first  during  childhood.  In 
those  who  speak  only  one  language,  it  may  suppress  separately  a  portion 
of  it,  such  as  the  substantives,  which  are  the  proper  names  of  objects. 


AUDITORY  INNERVATION  625 

Ideas  of  space  ;    their  relation  to  the  cortex  and  the  different  senses 

We  owe  to  Ewald  an  experiment  which  shows  the  comparative  part 
played  by  the  labyrinth,  the  cerebral  cortex,  and  the  different  senses 
in  the  conception  of  space  and  the  preservation  of  equilibrium. 

This  experiment  is  made  on  the  dog,  and  consists  in  effecting  methodi- 
cal ablations  of  the  two  labyrinths,  and  the  two  tactile  areas,  and  in 
verifying  after  each  operation  the  immediate  effects  and  the  permanent 
deficiency  resulting  from  these  ablations. 

Suppression  of  the  ideas  of  space  of  labyrinthine  origin. — After  complete  abla- 
tion of  one  labyrinth,  the  animal  displays  disturbances  both  of  audition  and  of 
the  muscular  movements.  The  first  are  permanent,  the  specific  function  cannot 
be  rej^Iaced  ;  the  second  ameliorate  and  seem  to  disappear  at  the  expiration  of  a 
variable  period  of  some  weeks.  The  ablation  of  the  second  labyrinth  brings 
about  bilateral  deafness,  and  completes  and  renews  the  disturbances  of  locomo- 
tion, which  are  reproduced  with  greater  severity,  but  they  in  their  turn  improve, 
and  after  several  months  the  animal  will  perform  all  its  movements,  whether 
instinctive,  voluntary,  or  acquired,  ajiparently  with  perfect  precision. 

Suppression  of  the  ideas  of  space  of  tactile  origin. — Afte:  wards  the  area  called 
motor,  but  in  reality  tactile,  of  the  cerebral  cortex  of  one  side  is  removed.  The 
consecutive  disturbances  are  those  observed  in  an  animal  which  has  not  under- 
gone previous  lesion  of  its  auditory  organs.  The  sensori-motor  paralyses  which 
result  from  this  cortical  lesion  continue  to  ameliorate,  and,  though  certain  acquired 
movements  may  have  disappeared,  locomotion  may  at  the  end  of  some  time  be 
considered  as  entirely  re-established.  Then  a  fourth  oiaeration  is  performed, 
consisting  in  the  ablation  of  the  second  cortical  tactile  area.  Motor  disturbances 
then  appear  which  surpass  in  gravity  all  which  it  has  been  possible  to  observe 
after  lesions  of  the  portions  of  the  nervous  system  governing  movement.  The 
dog  can  then  neither  jump  nor  run.  nor  walk,  can  neither  hold  itself  upright,  nor 
even  lie  down  on  the  abdomen  and  the  chest  :  it  lies  on  one  or  the  other  side,  and 
the  most  violent  movements  of  its  limbs  no  longer  succeed  in  raising  it. 

Preservation  of  the  ideas  of  space  of  visual  origin, — But  the  movements  of  the 
head  are  preserved  ;  it  turns  the  head,  and  also  the  eyes,  in  the  direction  of  the 
movements  it  desires  to  perform,  or  to  look  at  the  persons  or  objects  which 
interest  it.  After  some  days  it  uses  the  head  as  a  limb,  and  leans  the  muzzle  on 
the  ground,  so  as  to  make,  with  the  help  of  the  neck  and  trunk,  an  attempt  to 
raise  its  body. 

In  this  disorganized  condition  of  its  nervous  system,  the  animal  is  still  capable 
of  a  certain  amount  of  re-education  as  regards  locomotion  ;  but,  on  one  condition, 
viz.  :  that  it  is  left  in  the  light.  Shut  up  in  darkness,  it  remains  quite  incapable 
of  standing  up.  And  after  this  partial  re-education,  if  light  is  wanting,  the  most 
simple  automatic  movements  are  difficult,  if  not  impossible. 

As  the  result  of  each  of  these  fovu-  operations,  the  animal  has  lost  one  of  the 
apparatus  which  furnish  it  with  information  regarding  the  position  of  its  body 
and  its  limbs  in  relation  to  surrounding  objects,  and  also  as  to  its  own  segmentary 
attitudes.  After  the  ablation  of  the  two  labyrinths,  it  lost  the  api^aratus  which 
fiu-nished  the  most  definite  ideas  of  space,  and  those  wliich  are  most  frequently 
made  use  of,  because  they  are  rather  of  a  reflex  than  a  conscious  order  (sense  of 
space  of  labyrinthine  origin).  After  the  ablation  of  the  two  tactile  areas,  it  lost 
in  addition  the  tactile  and  muscular  sense  (tactile  sense  of  space).  After  the  two 
first  operations  affecting  the  labyrinths,  it  succeeded  in  bringing  about  an  appar- 
ently complete  re-education  of  its  movements  of  locomotion  or  otherwise,  because 

P-  S  S 


626  SPECIAL  INNERVATIONS 

it  still  had  at  its  disposition  several  senses,  and  more  particularly  the  tactile 
sense.  After  the  removal  of  its  two  tactile  areas,  it  lost  at  the  same  time  the 
labyrinthine  sense  of  space,  and  the  tactile  sense  of  space.  It  is  true  that  these 
two  latter  operations  are  not  rigorously  equivalent  to  the  two  former  ones  since, 
instead  of  abolishing  the  peripheral  apparatus  for  the  reception  of  tactile  stimiili 
(which  is  impossible),  a  central  ajjparatus  has  been  suppressed,  whose  associations 
preside  simultaneously  over  reflex  acts  like  the  former  (but  while  allowing  at  the 
same  time  others  to  subsist  in  the  subjacent  ganglia)  and  psychical  acts  (which 
introduces  a  functional  deficiency  of  a  new  character).  But  the  disturbance  of 
tlie  sense  of  space  has  none  the  less  been  extreme,  and  has  caused  all  the  latent 
sympton^s  of  the  labyrinthine  destruction  to  reappear. 

After  the  loss  of  two  senses  out  of  five  there  still  remains  one  available  to  the 
animal,  the  last  which  can  provide  it  with  information  concerning  the  space 
surrounding  it  and  to  bring  into  operation  the  sjDatial  sense  :  this  is  vision.  Thus 
we  see  that  it  makes  use  of  this  sense  to  orientate  its  efforts  and  its  movements, 
and  to  re-acquire,  by  means  of  a  longer  and  more  laborious  education  than  the 
preceding,  the  power  of  standing  up  and  of  walking. 

Part  taken  by  the  cerebellum. — It  must  be  remarked  that,  however  serious  and 
extensive  it  may  appear  to  be,  the  mutilation  inflicted  on  the  animal  has  still 
allowed  of  the  svibsistence  in  it  of  associations  which  are  either  important  or 
essential  for  equilibration  and  co-ordination  of  movements.  We  have  already 
said  that  the  tactile  sense,  though  very  much  con^promised  in  certain  respects, 
is  not  completely  abolished  as  regards  its  relations  with  locomotion.  Reflex 
associations  continue  between  the  sensory  extremities  (cutaneous,  articular, 
and  muscular)  and  the  motor  nerves  through  the  cerebral  ganglia  and  the  grey 
medullary  axis,  and  especially  by  means  of  that  pre-eminently  associating  and 
co-ordinating  organ,  the  cerebellum.  On  the  other  hand,  the  brain,  from  the 
psychical  point  of  view,  has  only  lost  its  tactile  area,  and  has  consequently  pre- 
served those  conscious  associations  which  act  as  a  guide  to  the  re-education  of 
the  nervous  system. 

The  sense  of  sight  is  intact  from  a  point  of  view  which  is  as  much  psychical  as 
reflex  or  automatic.  The  labyrinthine  sense  (sj^ecificallj^  auditory  and  spatial) 
is  out  of  court  on  account  of  its  incapability  of  furnishing  any  impulse.  The 
tactile  sense  (general  and  muscular  sensibility)  is  psychically  and  reflectively 
incomplete,  but  partially  subsists  from  a  more  specially  automatic  point  of  view. 
The  central  apparatus  of  motor  association  and  co-ordination,  the  cerebellum, 
continues  in  its  entirety,  and  again  utilizes  with  the  aim  in  view  of  locomotion 
and  equilibrium,  the  ideas  of  space,  at  first  discordant,  which  reach  it  from  the 
subsisting  sensory  and  sensorial  areas. 

Specific  and  common  nature  of  functions  ;  mechanism  of  the  substitutions. — 
Not  one  of  the  suppressed  apparatus  can  be  considered  as  useless,  and  after  the 
disappearance  of  each,  it  is  not  speciflcally  and  entirely  replaced  in  the  nervous 
functions.  But,  as  the  specific  nature  of  each  is  only  the  result  of  a  differentia- 
tion or  an  elaboration  of  the  function  common  to  all,  it  follows  that  substitutions 
are  possible  to  a  very  great  degree.  These  substitutions  come  into  being  the 
more  speedily  and  effectively  in  proportion  to  the  number  of  the  subsisting 
specific  organs,  so  that  from  this  fact  alone  the  jDossible  combinations  of  associa- 
tion become  more  numerous.  The  cerebellum  itself  may  be  removed,  provided 
that  the  brain  and  the  senses  are  retained. 

D.     PATHS    OF    RETURN 
Like  all  sensory  and  sensorial  systems,  the  auditory  system  has  its 
paths  of  return  or  of  reflexion,  which,  either  from  the  cortex  or  the 
subjacent  ganglia,  conduct  the  impulses  to  the  exterior. 


AUDITORY  INNERVATION  627 

The  motor  organs  on  which  the  impulse  is  reflected,  either  from  the 
cortex  or  the  ganglia  of  the  base  of  the  brain,  are  the  muscles  of  the 
external  ear  and  the  more  deeply  situated  ones  of  the  middle  ear. 

1.  Stimulation  of  the  cortex. — When  this  is  effected  in  the  temporal 
region  in  animals,  contraction  of  the  muscles  of  the  ear  is  the  effect  pro- 
duced by  it  ;  this  stimulation  further  reacts  on  the  rotatory  muscles 
of  the  head  and  the  eyes  to  turn  them  in  a  determinate  direction. 

2.  Muscles  of  the  concha. — The  muscles  of  the  concha  in  man  play 
an  extremely  restricted  part  and  are  nearly  obliterated.  In  animals 
they  answer  the  purpose  of  directing  the  auricular  aperture  in  the 
direction  required  for  collecting  the  sonorous  waves,  almost  in  the 
same  manner  as  the  oculo-motor  muscles  turn  the  visual  axis  in  different 
directions.  It  is  the  facial  nerve  which  provides  the  auricular  muscles 
with  their  motor  branches. 

In  order  to  proceed  from  the  cortex  to  the  motor  nuclei  of  the  bulb  and  the 
pons,  the  motor  impulse  follows  fibres  contained  in  the  external  bundle  of  the 
crusta  of  the  cms  cerebri  (cortico-pontine  path).  Another  portion  of  these  fibres 
appears  to  rejoin  these  nuclei  by  a  more  devious  path,  which  passes  tlirough  the 
optic  thalamus,  whence  in  their  turn  they  reach  the  grej"  bulbo-pontine  matter. 
The  first  of  these  two  motor  paths  is  devoted  to  voluntary  movements,  the  second 
to  the  movements  of  emotional  expression,  according  to  a  division  of  attributes 
wlaich  appears  to  exist  for  all  the  senses  and  the  motor  combinations  associated 
with  them. 

3.  Muscles  of  the  middle  ear. — These  have  an  equally  precise  function,  but  one 
of  another  order.  The  muscle  of  the  malleus,  by  its  contraction,  renders  the 
tympanic  membrane  tense,  making  it  project  into  the  tjTnpanic  cavity,  and 
thus  increases  the  intra-labyrinthine  pressvu-e.  The  muscle  of  the  stapes,  by  its 
contraction,  on  the  contrary,  relaxes  this  membrane,  and  lowers  the  pressure  in 
the  labyrinth.  The  fii'st  of  these  muscles  receives  its  motor  fibres  from  the  tri- 
geminal :    the  second  from  the  facial. 

Fi.u"ther,  vaso-motor  reflexes  (with  bulbar  centres)  take  part  in  maintaining 
(or  in  re-establishing  after  disturbance)  the  equilibrium  of  the  tensions  between 
the  lymph  of  the  internal  ear  and  the  air  of  the  tympanic  cavity. 

The  adapting  and  compensating  mechanisms  which  take  part,  by  reflex  stimula- 
tion, in  the  exercise  of  audition  and  of  orientation,  will  be  examined  in  the  stvidy 
of  the  organs  of  the  senses. 

Functional  analogy. — The  analogy  of  function  between  the  muscles 
of  the  auditory  ossicles  and  the  ciliary  muscles  of  the  eye  is  sufficiently 
great  to  have  at  once  arrested  the  attention  of  observers.  Obviously, 
these  muscles  obey  solicitations  of  reflex  order,  which  are  controlled 
and  regulated  by  auditory  stimulation.  It  is  probable  that  the  reflex 
system  to  which  they  belong  closely  resembles  in  its  arrangement  that 
of  the  pupil,  and  that  its  centre  of  reflexion  is  situated  in  the  region 
of  the  corpora  quadrigemina  ;  but  we  possess  no  convincing  experi- 
mental evidence  in  support  of  this  inference. 

SS* 


CHAPTER    IV 
OLFACTORY  AND  GUSTATORY  INNERVATIONS 


Light,  sound,  and  the  mechanical  actions  of  bodies,  which  are  the 
stimuh  of  our  three  principal  senses,  are  physically  known  to  us.  We 
cannot  say  as  much  as  concerns  S7nell  and  taste,  which  for  us  are  only 
sensations  and  have  in  themselves  no  scientifically  defined  objective 
character.  Placed,  the  one  at  the  entrance  of  the  respiratory,  and  the 
other  at  that  of  the  digestive  paths,  the  senses  of  smell  and  taste  give 

us  information  concerning  certain  quali- 
ties, either  of  the  air  we  breathe,  accom- 
panied by  odours,  or  of  the  food  we 
introduce  into  the  stomach  after  its  pre- 
paration for  swallowing  in  the  mouth. 

At  first  sight  it  would  seem  that  these 
senses  serve  as  a  means  of  preservation 
and  immediate  defence  against  the 
dangers  which  may  threaten  us  through 
the  paths  of  nutrition.  This  action  of 
instinctive  defence  is,  however,  a  restricted 
one  ;  for  very  poisonous  substances  may 
be  quite  odourless  and  tasteless. 

The  olfactory  and  gustatory  sensations 
in  man  do  not  possess  an  importance  in 
any  way  comparable  to  that  of  the  senses 
already  considered,  and  the  analysis,  both 
objective  and  subjective,  we  can  make 
of  them,  gives  us  less  detail  and  allows  of 
epithelial  cells  of  support ;  h  olfactory  fcwcr  poiuts  of  vicw  than  as  regards  the 

It  is  reduced  to  a  problem 
of  localization,  which  is,  however,  but 
imperfectly  solved. 


Fig. 


In 


250. — Elements     of 
Olfactory  epithelium. 

1,   elements    in    the    frog  ; 


the 


cells;  with   a   deep   prolongation     (d)    ^^^^^   ^^^^^^ 
and    a    superncial    prolongation   (c), 
and  with  its  terminal  cilia  (e)  . 

In  2.  Same  elements  in  man, 
similar  lettering. 

In  3.  Nerve  fibres  of  the  olfactory 
nerve  in  the  dog,  their  terminal  sub- 
divisions in  a  (Frey). 


A.     OLFACTORY    SYSTEM 
At  the  present    time   it  is   principally 
from  morphology  that  we  must  seek  information  concerning  olfactory 
innervation.     Experiment  points  out  the  pituitary  mucous  membrane 


OLFACTORY  AND  GUSTATORY  INNERVATIONS 


629 


as  being  the  seat  of  olfactory  impressions,  not,  however,  in  its  whole 
extent,  but  only  in  the  superior  portion  of  the  nasal  fossae. 

Field  for  the  reception  of  impressions. — Special  cells  {olfactory  cells) 
which  are  continuous  with  the  hbres  of  the  olfactory  nerve,  exist  in 
this  portion  of  the  mucous  membrane.  These  elements,  intercalated 
between  the  epithelial  cells  of  the  mucous  membrane,  assume  the  form 
of  elongated  rods,  ciliated  on  the  mucous  surface  ;  they  possess  a 
nucleus  by  which  they  are  increased  in  size,  and  a  moniliform  pro- 
longation which  attaches  them  to  the  olfactory  fibres  contained  in  the 
bundles  which  pass  through  the  cribriform  plate  of  the  ethmoid  bone. 
Thus  they  form  neurons  whose  cells,  located  in  the  mucous  membrane, 
have  a  cihated  receptive  pole  of  very  simple  form,  the  axon  of  which 
terminates  in  the  small  rounded  masses  which  are  the  glomeruli  of  the 
olfactory  bulb.  Such  is  the  jjeripheral,  or  injerior,  neuron  of  the 
system. 

1.    Bulbar  portion  of  the  system 

Olfactory  bulb. — Situated  in  the  interior  of  the  skull,   the  olfactory 
bulb  is  a  primary  ganglion,  analogous  to  the  bulbar  nuclei  of  the  audi- 
tory nerve,  or  to  the  grey 


columns  of  the  spinal  cord 
which  receive  the  posterior 
roots,  but  by  no  means  to 
the  ganglia  of  Corti  and 
Scarjja,  or  to  the  spinal 
ganglia,  as  has  been  some- 
times held.  The  olfactory 
nerve  (such  as  we  must 
understand  it)  being  made 
Tip  merely  of  those  fibres 
which,  arising  in  the 
pituitary  mucous  rnj?m- 
brane,  traverse  the  cribri- 
form plate  in  order  to 
terminate  in  the  olfactory 
bulb,  its  cells  of  origin  re- 
tained in  the  mucous 
membrane,  form  there  a 
sort    of    dissociated    and 


Mitral  cell 


■  Cent,  path 


Glomerulus 


'  Periph.  path 


,>.—  OH.  cell 
Olf.Epith. 


Fig.  251. — Olfactory  paths. 

Peripheral  neuron  (olfactory  cell)  and  deep  neuron 
(mitral  cell). 

Connexions  of  the  terminal  polar  fields  of  the  first 
and  initial  polar  fields  of  the  second  in  the  glomerulus. 


spread-out  ganglion,  which  is  in  all  respects  the  equivalent  of  a  spinal 
ganglion. 

The  olfactory  bulb  has  the  appearance  of  a  mass  of  grey  matter, 


630  SPECIAL  INNERVATIONS 

containing  not  only  cells,  but  also  polar  arborizations  of  the  same  cells, 
by  means  of  which  they  carry  out  their  functional  associations.  It  is  a 
relay,  a  locality  of  association,  and  consequently  of  distribution  and  of 
transformation  of  the  impulse. 

Its  organization. — Histological  examination  of  this  "  centre  "  reveals  in  it 
details  of  great  interest.  The  olfactory  bulb  contains  the  terminations  of  the 
olfactory  fibres  (those  having  their  receptive  pole  and  their  cell  of  origin  in  the 
olfactory  mucous  membrane)  ;  it  contains,  on  the  other  hand,  special  cells  of 
different  categories.  The  principal  element  is  the  mitral  cell,  so  called  on  account 
of  its  resemblance  to  the  mitre  of  a  bishop.  From  the  apex  of  this  mitre  an  axon 
arises,  which,  following  the  olfactory  tract,  proceeds  to  the  brain.  Its  borders 
and  its  base  throw  out  protoplasmic  prolongations  (dendrites)  which,  taken  as 
a  whole,  represent  its  receptive  pole.  These  prolongations  have  different  con- 
nexions, and  it  will  be  necessary  to  examine  them  separately.  Finally,  it  con- 
tains the  terminations  of  a  variety  of  very  singular  elenaents,  of  which  the  other 
senses,  and  especially  the  optic  nerve,  furnish  us  with  examples.  It  receives 
from  the  brain  elements  whose  conduction  is  obviously  centrifugal,  which  convey 
to  it,  through  a  purely  sensorial  organ,  descending  impulses  of  the  nature  of  those 
furnished  by  the  brain  to  the  grey  axis  of  the  spinal  cord,  or  by  this  latter  to  the 
motor  organs  of  the  periphery. 

Connexions  between  the  olfactory  fibres  and  the  mitral  cells. — Those  which  are 
continuous  with  the  base  of  the  mitral  cell  descend,  so  to  speak,  in  order  to  meet 
the  terminations  of  the  olfactory  fibres.  The  connexions  between  these  two 
orders  of  fibres,  representing  the  opposite  poles  of  two  successive  neurons,  are 
effected  in  small  masses  isolated  the  one  from  the  other,  the  glomeruli  of  the 
olfactory  bulb.  Nowhere  can  the  connexions  between  the  nervous  elements 
transmitting  the  impulse  be  better  seen  than  in  these  small  masses,  made  up  of 
grey  matter  without  cells.  The  nerve  cell  (by  this  being  imjolied  the  mass  of  primi- 
tive protoplasm  which  has  remained  more  visible  in  the  surroundings  of  the 
nucleus)  is  therefore  not  necessarily  the  portion  of  the  neuron  receiving  the  im- 
pulse. The  function  of  the  differentiated  portions  (the  dendrites)  is  the  collection 
of  this  impulse  and  its  direction  in  the  paths  it  must  follow  in  the  cell,  by  causing 
it  to  converge  on  the  axon. 

In  an  example  of  this  nature  everything  is  interesting,  because  under  its  simple 
form  it  supplies  us  with  essential  data  concerning  the  organization  of  the  nervous. 
system.  The  glomerulus  displays  to  us  relations  between  the  terminal  and 
initial  portions  of  two  neurons  placed  in  succession.  It  is  generally  naaintained 
that  this  connexion  is  effected  by  contiguity,  with  interruption  of  the  nervous 
matter  properly  so  called.  The  mechanism,  certainly  of  an  extremely  delicate 
nature,  of  the  transmission  of  the  impulse,  at  the  present  moment  is  completely 
unknown  to  us.  The  hypotheses  which  may  be  made  on  this  subject  need  stand 
in  no  fear  of  contradiction,  as  they  cannot  be  submitted  to  experimental  in- 
vestigation. 

Numerical  relations. — Though  the  functional  natiire  of  these  connexions, 
remains  unknown  to  us,  we  may  nevertheless  observe,  in  the  manner  in  which 
they  are  carried  out,  interesting  details.  In  man,  each  olfactory  cell  is  connected 
by  a  single  axis-cylinder  prolongation  with  a  single  mitral  dendritic  prolongation,, 
ramified  at  the  meeting-point  of  one  with  the  other  in  the  glomerulus,  rarely  with 
two  of  these  prolongations.  But  there  is  not  on  this  account  either  augmentation 
or  reduction  in  the  number  of  neurons  placed  in  succession,  this  being  exceptional 
in  connexions  of  this  nature. 

In  reptiles  and  batrachia,  each  mitral  cell  is  provided  with  from  two  to  five 


OLFACTORY  AND  GUSTATORY  INNERVATIONS         631 

dendritic  prolongations  which   collect   the  impulse   from  an  equal   number    of 
olfactory  fibres  into  as  many  distinct  glomeruli  (P.  Ramon). 

In  birds  there  are  mitral  cells  which  display  as  many  as  twenty  dendritic  or 
protoplasmic  prolongations  spreading  out  in  as  many  glomeruli.  Here  obviously 
is'a  reduction  in  number  of  the  neurons  in  the  direction  of  the  transmission  of 
the  impulse. 

Tn  the  dog,  the  arrangement  is  the  reverse  ;  when  the  olfactory  fibre  reaches 
a  glomerulus,  it  there  enters  into  comiexion  with  five  or  six  dendi'itic  prolonga- 
tions belonging  to  as  many  distinct  mitral  cells.  Here  we  find  augmentation 
of  the  nmnber  of  neurons  in  the  direction  of  the  current  of  stimulation. 

Functional  varieties. — It  is  quite  certain  that  these  differences  in  the  associa- 
tions of  the  glomeruli  coi-respond  to  functional  varieties.  In  the  inferior  verte- 
brata,  the  parallel  repetition  of  the  olfactory  cells  and  fibres  corresponds  to  an 
enlargement  in  siirface  of  the  field  of  reception  for  olfactory  impressions  on  the 
pituitary  mucous  membrane.  In  the  dog  and  the  osmatics,  the  multiphcation 
of  the  mitral  cells  which,  in  the  same  glomerulus  come  into  cormexion  with  the 
same  olfactory  fibre,  should  correspond  (like  the  augmentation  of  the  cerebral 
olfactory  system  in  these  animals)  to  an  elaboration  of  the  sensation  itself. 

The  osmatics,  when  compared  with  man  and  the  primates,  present  a  double 
increase  in  their  olfactory  power,  namely  :  (1)  through  the  absolutely  larger 
number  of  their  olfactory  cells  and  fibres,  corresponding  to  the  extension  of  the 
sensorial  area  of  the  pituitary  mucous  membrane  ;  (2)  through  the  relatively 
equally  increased  number  of  their  mitral  cells  with  regard  to  the  first,  this  in- 
crease in  number  of  the  deep  elements  proceeding  pari  passu  with  a  continually 
increasing  complexity  of  their  connexions  both  between  themselves  and  with 
other  elements. 

Other  connexions  of  the  mitral  cells. — By  their  angles  the  mitral  cells  give  off 
other  dendritic  prolongations  somewhat  similar  in  shape  to  the  preceding,  but 
whose  direction  is  different  and  which  have  no  relation  with  the  glomeruli  and 
the  olfactory  fibres.  These  prolongations  are  on  one  side  in  contact  with  small 
cells  having  limited  expansions,  the  granules,  which,  rare  in  fish  and  reptiles, 
begin  to  be  numerous  in  birds,  and  still  more  so  in  mammals.  Here  may  be  seen 
cells  of  association  mutually  solidarizing  or  systematizing  a  certain  number  of 
mitral  cells.  The  same  lateral  prolongations  of  the  mitral  cells  come  again  into 
contact  with  the  terminal  arborizations  of  the  elements  of  centrifugal  conduction, 
which  have  been  found  to  exist  in  the  olfactory  tract  (Van  Gehuchten)  and  convey 
an  impulse  of  cerebral  origin  to  the  olfactory  bulb. 

The  descending  or  centrifugal  conduction  of  these  elements  is  not  a  fact  estab- 
lished by  experiment,  but  may  be  affirmed  (like  that  of  the  similar  elements  of 
the  optic  nerve)  from  the  orientation  of  these  elements  in  the  olfactory  tract, 
•which  orientation  is  exactly  the  contrary  to  that  of  the  axons  appertaining  to 
the  obviously  sensorial  or  centripetal  mitral  cells. 

The  mitral  cells,  or  at  least  the  articulations  of  their  lateral  prolongations  with 
the  preceding  elements,  appear  to  be  the  seat  of  a  reflexion  of  the  impulse,  effected 
in  the  opposite  direction  to  the  one  we  are  acquainted  with,  and  of  which  the 
grey  matter,  wherever  existing,  supplies  so  many  examples. 

If  we  recall  what  has  been  said  above  with  regard  to  the  nmiierous  relations 
between  the  cells  and  olfactory  fibres  and  the  mitral  cells,  we  shall  see  that,  even 
in  animals  in  which  these  relationships  assume  the  most  simple  modality,  without 
apparent  reduction  or  increase  of  the  ntmnber  of  the  neurons  in  connexion,  the 
impulse,  in  surmounting  the  ganglionic  halting-place  where  these  connexions 
come  into  being,  finds  new  conditions,  and  enters  into  conflict  with  impulses  of 
internal  or  external  origin,  which  transform  it  from  this  moment  by  sending  it 
forward  and  preparing  it  for  other  successive  transformations. 


632 


SPECIAL  INNERVATIONS 


Collaterals  ;  pyramidal  cells. — ^The  axons  of  the  mitral  cells  which  direct  the 
impulse  towards  the  brain  in  localities  which  will  be  defined  later  on,  have  already 
partially  allowed  it  to  flow  away  in  the  olfactory  tract  by  collaterals  arranged 
in  series  throughout  its  length  :  these  transmit  it  to  fresh  cells  belonging  to  the 
grey  matter  of  the  tract  (peduncle  in  animals)  :  these  cells,  of  small  size  and  of 
pyramidal  form,  direct  it  anew  by  distinct  paths  towards  the  brain.  Here  again 
is  another  example  of  the  arrangement,  so  often  pointed  out,  of  doul^le  paths, 
one  direct  and  rapid  (by  fibres  of  projection  to  a  great  distance),  the  other  indirect, 
slower  and  broken  by  relays  (short  paths  of  the  grey  matter),  which  present 
themselves,  so  to  speak,  to  every  impulse,  diffuse  and  disseminate  it,  and  so 
multij^ly  its  associations  and  its  conflicts,  that  at  last  nothing  of  the  initial  form 
of  the  impulse  is  left  subsisting  in  the  surface  receiving  the  impression. 

2.    Cerebral  portion 

The  olfactory  tract  is  connected  with  the  brain  by  four  roots  :  one, 
external  ivhite,  which,  after  having  crossed  the  fissure  of  Sylvius,  is  lost 
in  the  antero-external  portion  of  the  hippocampal  convolution  ;  one, 
internal  ivhite,  which  reaches  the  mesial  surface  of  the  cerebral  hemi- 
sphere and  is  lost  in  the  region  known  as  that  of  the  olfactory  commissure 
towards  the  front  of  the  convolution  of  the  corpus  callosum  ;  a  grey  or 
^^-^.^-^  middle    root,    which, 

// ^''~-  ~"^\  plunging     into     the 

grey  matter  of  the 
anterior  perforated 
space,  penetrates  to 
a  large  extent  into 
the  head  of  the  corpus 
striatum  and  joins 
the  anterior  white 
commissure  of  the 
l)rain.  As  regards 
the  fibres  involved 
in  this  commissure, 
they  all  cross  to  the 
opposite  side  ;  but 
some  proceed  to  the 
opposite  olfactory 
bulb,  and  others  to 
the  cerebral  cortex 
of  the  opposite  side. 
Finally,  a  superior 
root  (also  mingled  with  grey  matter)  is  lost  in  the  posterior  portion 
of  the  two  orbital  convolutions. 

To  sum  up,  these  four  roots  terminate  in  a  hijDpocampal  region 
(external  white    root),  in   a   callosal  region  (internal   white   root),  in 


Call,  centre..^ 


Front  C. 


Int.  Root. 


Temp.  C. 


Fig.  252. 


-Cortical  centres  of  olfaction  (after  Charpy). 

The  olfactory  tract  has  been  cut  and  its  cerebral  end  turned 
backwards,  in  order  to  unco\-er  a  subjacent  area  of  the  grey 
inatter  appertaining  to  olfaction. 


OLFACTORY  AND  GUSTATORY  INNERVATIONS        633 

an    orbital  region    (superior    root),  and  a    temporal    region  (middle 
root). 

a.  Hippocam^^al  region. — The  olfactory  area  thus  described  corresponds  more 
especially  to  the  crotchet  or  uncus  of  the  hippocanipal  convolution.  Further,  the 
cornu  ammonis  is  included  in  it,  and  this  connexion  is  effected,  either  by  fibres 
which  pass  to  this  structure  directly  from  the  white  external  root,  or  by  fibres 
which,  proceeding  from  the  white  internal  (or  even  the  middle  root),  follow  the 
devious  course  of  the  trigon  to  return  finally  to  the  cornu  atnmonis. 

b.  Callosal  region. — This  includes  the  olfactory  chiasma,  the  point  of  union 
between  the  j^osterior  extremity  of  the  internal  frontal  with  the  convolution  of 
the  corpus  callosum  ;  and,  further,  the  adjacent  portion  of  this  last  convolution 
(as  far  as  the  knee  of  the  corjDus  callosum). 

c.  Orbital  region. — This  includes  the  posterior  portion  of  the  two  orbital  con- 
volutions up  to  the  cruciform  fuiTow  (in  the  himian  brain).  In  completely  anos- 
matic  animals  like  the  dolphin,  this  posterior  portion  is  quite  smooth  and  atro- 
phied, whence  the  name  of  olfactory  desert  given  it  by  Broca. 

d.  Temporal  region. — This  region,  in  which  are  supposed  to  terminate  those 
fibres  which  have  traversed  the  median  line  in  their  progress  to  the  cortex  of  the 
opposite  hemisphere,  is  very  little  known,  and  is  perhaps  merely  a  prolongation 
of  the  hippocampal  region. 


Lirribir  lobe 


Sup.  arc. 


Inf.  arc. 


Pel. 


Limbic  convolution  of  the  osmatics. — All  sensory  or  sensorial  systems 
have  a  cyclic  arrangement,  to  which  we  have  already  directed  attention. 
In  the  olfactory  system,  the 
general  anatomical  structure 
seems  to  display  this  exter- 
nally, so  that  it  becomes  per- 
fectly obvious.  As  Broca 
was  the  first  to  remark,  this 
sensorial  system,  so  import- 
ant in  certain  species,  is 
developed  around  the  corpus 
callosum  perpendicularly  to 
the  transverse  direction  of 
the  fibres  of  this  great  com- 
missure, and  is  represented 

by  a  convolution  in  the  shape  of  a  ring  or  limbus,  the  limbic  con- 
volution, lying  on  the  mesial  aspect  of  the  cerebral  hemisphere. 
Somewhat  dissociated  in  man,  in  whom  it  is  subdivided  into  two 
arched  convolutions  united  by  their  anterior  and  posterior  ex- 
tremities, the  one  above  the  corpus  callosum  (convolution  of  the  corj^us 
callosum),  the  other  below  (hippocampal  convolution),  this  convolution 
is  distinctly  continuous  in  the  osmatics  (animals  with  highly  developed 
sense  of  smell  :  dog,  otter,  fox,  etc.),  to  such  a  degree,  indeed,  that, 
starting  from  the  olfactory  lobe  and  jDcduncle  by  following  its  internal 


O//.  lobe 

Fig.   253. — Diagram  of  the  limbic  lobe, 
in  the  form  of  a  racket. 


634  SPECIAL  INNERVATIONS 

root,  the  boundaries  of  the  whole  corpus  callosum  will  be  traversed, 
of  which  the  superior  surface  the  splenium,  and  the  inferior  surface 
will  be  successively  followed  in  order  to  regain  the  peduncle  by  its 
external  root.  Hence  arises  the  comparison  of  this  aggregation  to  a 
playing  racket,  of  which  the  olfactory  peduncle  would  be  the  handle 
and  the  convolution  itself  the  enclosed  network.  This  latter  is  com- 
pleted by  other  circular  formations  Avhich,  either  above  or  below  the 
corpus  callosum,  form  concentric  circles  of  the  same  nature,  and  to 
which  we  shall  return  later  on. 

Osmatics  ;  anosmatics. — It  is  also  to  Broca  that  the  distinction 
drawn  between  osmatic  and  anosmatic  animals  is  due,  these  expressions 
being  replaced  by  Turner  by  those  of  macrosmatics,  microsmatics  and 
anosmatics  in  order  to  indicate  a  graduation  not  sufficiently  empha- 
sized by  the  preceding  epithets  ;  the  dog  is  macrosmatic  ;  the  dolphin 
is  anosmatic  ;  man  and  the  monkey  are  microsmatic.  Such  marked 
differences  in  the  exercise  of  so  important  a  function  (the  question  here 
is  of  a  sense  taken  in  its  entirety)  should  be  rendered  evident  by  in- 
equalities in  development  of  the  nervous  organs  corresponding  to  it, 
and  this  is  what  anatomy  and  comparative  physiology  have  demon- 
strated as  regards  the  sense  of  smell.  By  taking  as  a  guide  the  con- 
nexions by  which  to  the  external  organ  of  smell  (itself  highly  developed 
in  osmatics)  certain  convolutions  of  the  brain  are  attached,  there  will 
be  found  in  them  a  development  proportional  to  the  function  in  each 
species  under  consideration. 

Functional  localization  and  balance. — The  question  regarded  from 
this  point  of  view  reverts  to  that  of  the  cerebral  localization  of  the 
sense  of  smell,  which  comparative  anatomy  has  undertaken  to  solve, 
failing  definite  clinical  observations  and  experiments,  these  latter  being 
too  difficult  to  perform.  This  question  is  complicated  by  another 
which  by  no  means  diminishes  its  difficulties,  namely,  that  of  the  balance 
of  the  special  senses  capable  of  mutual  replacement  in  the  directive 
function  which  devolves  on  one  or  the  other,  according  to  the  particular 
evolution  of  the  species,  in  the  course  of  ph3^1ogenetic  development. 
We  have  already  pointed  out  a  functional  balance  of  another  nature, 
between  organs  or  systems,  not  juxtaposed,  but  superposed  ;  and  it  is 
thus  that  the  brain  in  the  superior  vertebrata,  in  the  primates  and 
specially  in  man,  monopolizes  by  centralization  those  federal  associa- 
tions which,  in  the  inferior  vertebrata,  are  organized  in  the  cerebral 
ganglia  or  in  the  spinal  cord,  and  in  the  in  vertebrata  in  the  ganglionic 
chain.  This  centralization  to  the  benefit  of  the  brain  does  not  operate 
without  a  differentiation  of  its  parts  and  of  its  functions,  and  a  kind  of 
fresh  metamerization,  which  is  more  or  less  marked  at  its  surface,  in 


OLFACTORY  AND  GUSTATORY  INNERVATIONS        635 

a  new  order.     This  corresponds  to  different  senses,  which  have  each 
chosen  a  special  territory  in  the  cortex. 

The  equivalence  of  these  different  sensorial  systems  does  not  imply 
their  equality.  In  the  progressive  develoiDment  of  the  brain,  they  are 
not  seen  to  take  an  equal,  or  even  proportional  part  ;  but,  on  the  con- 
trary, the  more  or  less  rapid  extension  of  one  amongst  them  progresses 
pari  jMSSu  with  the  partial  regression  of  another.  But  as  the  general 
morphology  of  the  brain  does  not  sensibly  alter  in  its  larger  features, 
or,  to  put  it  otherwise,  as  the  functional  associations  of  the  elements 
are  independent  of  the  external  form  of  the  brain — the  encroachment 
of  the  systems  on  each  other  may  come  about  without  leaving  very 
obvious  traces,  and  morphologically  equivalent  portions  may  be  found 
to  correspond  to  specifically  differentiated  functions,  in  the  chft'erent 
animal  species.  Nevertheless,  when  the  regression  is  very  marked, 
or  when,  conversely,  the  development  is  exaggerated,  more  or  less 
obvious  morphological  changes  may  be  recognizable  on  the  surface  of 
the  brain ;  and  this  is  what  stands  prominently  displayed  in  a  com- 
parison between  the  brains  of  the  macrosmatics  and  the  anosmatics, 
in  spite  of  the  difficulties  arising  from  the  want  of  definite  boundaries 
l^etween  the  different  sensorial  areas. 

Indefinite  boundaries  ;  mutual  dependence  of  functionally  differentiated  portions. 


Ext.  marj.  arc. 


Int..  i.iarj.  arc. 


01  f.  Fed 


Corp.  call. 


Fimbria 


Bent,  body 


Fig.  254. — System  of  olfactory  association. 
Internal  and  external  marginal  arcs  (diagrammatic.     Charpy). 


— It  is  important,  however,  to  remember  that,  in  the  strict  sense  of  the  word, 
such  limitations  do  not  exist.  If  at  the  periphery  of  the  body  the  sensorial  areas 
are  distinctly  defined  and  without  mutual  connexions,  this  is  not  so  at  the  surface 
of  the  brain  which  receives  their  fibres  of  projection.  The  areas  for  the  reception 
of  the  impulses  conveyed  by  the  fibres  of  projection  of  each  special  sense  are 
very  distinct  from  each  other,  but  are,  in  addition,  mutually  connected  by  fibres 


636  SPECIAL  INNERVATIONS 

of  association,  and  these  are  more  numerous  than  the  elements  of  projection 
themselves.  From  this  fact  it  will  he  seen  that  there  is  no  sense  whose  functional 
activity  does  not  reverberate  through  the  ivhole  brain,  and  by  it  through  the  whole 
organism,. 

The  word  centre,  so  often  employed  to  describe  these  sensorial  cortical  terri- 
tories, should  be  understood  as  implying  foci,  not  only  of  reflexion  on  the  spot  by 
descending  fibres  of  projection,  but  also,  and  principally,  of  radiation  in  the 
cerebral  substance  ;  the  brain  being,  like  the  spinal  cord,  but  to  a  still  greater 
extent,  an  elective  organ  of  dispersion  and  distribution  of  the  impulses  reaching 
it  by  localized  and  specialized  paths,  it  permits  these  impulses  to  flow  away  after 
multiplied  transformations  by  functionally  specialized  and  localized  descending 
paths  connected  with  the  preceding  and  according  to  all  possible  combinations. 

External  and  internal  marginal  arc. — The  limbic  convolution  of  Broca  rej^re- 
sents  tlie  ideally  simplified  scheme  of  the  olfactory  system.  In  reality  this  scheme 
is  complicated  by  the  adjunction  of  arched  tracts  of  white  fibres,  more  or  less 
mingled  with  grey  matter  or  interupted  by  ganglia,  which  reproduce  its  genera 
oval  form,  being,  as  they  are,  concentric  to  the  limbic  convolution  (M.  Duval, 
Schwalbe,  Giacomini,  Zukerkandl,  Trolard,  Bole).  The  olfactory  system,  to 
sum  up,  is  formed  of  three  concentric  circles.  The  external  one  is  the  limbic 
convolution  ;  inside  it  is  an  external  marginal  arc  comprehending  the  fascia  dentata 
and  the  nerves  of  Lancisi,  and  which  consequently  passes  above  the  corpus 
callosum.  The  third  is  an  internal  marginal  arc,  formed  by  the  fimbria,  the 
cerebral  trigon,  and  the  peduncle  of  the  septum  lucidum,  and  passes  below  the 
coi'piis  callosum  ;  perforating  fibres  unite  the  second  to  the  third  arc,  passing 
through  the  substance  of  this  latter. 

All  these  portions  present  tolerably  natiiral  mutual  connexions.  It  is,  however, 
impossible  to  say  in  what  degree  each  is  connected  with  the  exercise  of  smell. 

3.  Evolution  of  the  olfactory  system  and  of  its  function 

The  evolution  of  the  olfactory  s^^stem  in  the  zoological  series  forms 
an  interesting  chapter  of  comparative  physiology.  We  will  here 
endeavour  to  trace  the  principal  data  concerning  it. 

a.  Inferior  vertebrata. — In  fishes,  the  cerebral  cortex,  strictly  speaking,  does 
not  yet  exist,  being  merely  indicated  by  an  epithelial  layer  not  yet  differentiated. 
In  reptiles  it  is  distinctly  recognizable,  and  enters  into  communication  with  the 
olfactory  lobe,  though  the  other  senses  are  not  yet  directly  connected  with  it. 
"  The  brain  of  reptiles  is  an  olfactory  brain  "  (Edinger). 

The  sense  of  smell  is  not  wanting  in  fishes  ;  it  merely  shares  with  the  other 
senses  the  thalamus  and  the  basal  ganglia,  which  in  these  creatures  represent  the 
highest  differentiation  of  the  nervous  system  and  of  its  functions.  In  reptiles, 
the  new  and  exckisive  relations  of  the  olfactory  bulb  with  the  cerebral  cortex 
allow  of  the  subsistence  of  its  older  connexions  indicated  by  two  other  tracts 
proceeding  to  the  subcortical  ganglia.  One  of  these  tracts  reaches  the  ganglion 
habenulse  and  from  this  ganglion  a  descending  bundle  arises,  the  activity  of 
which  is  motor.  The  olfactory  impulses  are  thus  reflected  in  superposed  stages 
of  grey  matter,  viz.  :  the  habentda,  the  epistriatum  and  finally  the  cortex,  under- 
going, in  each  case,  a  transformation  of  superior  order  which  removes  them  from 
purelj^  automatic  acts. 

The  cortex  of  reptiles,  of  purely  olfactory  function,  consequently  corresponds 
to  the  cornu  ammonis  in  mammals,  and  to  their  limbic  lobe,  in  so  far  as  it  itself 
possesses  olfactory  function.  Here  also  may  be  recognized  a  kind  of  fornix  wliich 
is  distributed  between  a  genuine  corpus  mammillare  and  the  ganglion  habenijlse 
^Edinger). 


OLFACTORY  AND  GUSTATORY  INNERVATIONS        637 

b.  Superior  Vertebrata. — The  olfactory  system  in  man  being  taken  as  a  basis 
of  comparison,  we  see  its  different  portions  presenting  a  relative  increase  in  tlie 
osmatics,  and  an  equally  relative  atrophy  in  anosmatics,  unec^ually  distributed 
over  the  different  arcs  or  convolutions  of  this  system. 

Macrosmatics. — On  account  of  its  antiquity  (equally  relative)  in  ph^'logenetic 
development,  its  convolutions  are  the  first  to  be  sketched  in  those  species  where 
the  brain  from  being  lissencephalic  becomes  gyrencephalic.  At  an  early  period 
a  fiu'row  separates  the  peduncle  from  the  hippocamjDus,  thus  marking  the  exten- 
sion in  area  of  these  portions.  The  convolution  of  the  corpus  callosum  is  also 
one  of  the  first  to  be  sketched  in.  Its  bulb  and  its  peduncle  with  their  prolonga- 
tions assume  the  proportions  of  a  genuine  lobe  (olfactory  lobe). 

The  roots  of  the  peduncle  are  strong  and  the  middle  one  occupies  that  quadri- 
lateral space  which,  much  diminished  in  thickness  in  man,  ultimately  becomes 
the  anterior  perforated  spot  ;    it  is  this  same  root  whose  fibres  decussate  with 


G.  hjben.  Opt.  tlvd. 


T.  retrofl  ■ 


Pin.  gl. 


Tcenin  thai. 

Ant.  tub. 
Trigon  {ant.  p.) 


Stripe  of  Vicq  d'Azyr 
T.  of  the  tegumentum 
Mammill.  ped. 

Mammill.  tub. 


Pons 


Fig.  255. — Habenular  system  (blue)  and  mammillary  system. 
Sagittal  Section.     Diagrammatic  (Charpy). 


those  of  the  opposite  side  in  the  anterior  commissure,  and  which  further  furnishes, 
according  to  Broca.an  excito-reflex  tract  which  by  the  peduncle  rejoins  the  bulbo- 
medullary  centres,  whence  arise  the  motor  nerves.  These  roots  connect  the 
olfactory  lobe  to  three  regions  of  grey  matter  belonging  to  the  frontal  lobe  above, 
to  the  hippocampal  lobe  externally,  and  to  the  lobe  of  the  corpus  callosum  within. 
The  organization  of  the  internal  arcs  (external  and  internal  marginal)  is  in 
proportion. 

This  is  the  arrangement  in  osmatics  as  a  whole.  Even  in  these  animals,  and 
in  spite  of  their  coherent  appearance  as  a  whole,  we  are  not  authorized  to  connect 
these  different  portions  to  the  sense  of  olfaction  in  an  invariable  and  strict 
manner. 

Microsmatics. — In  microsmatics,  and  especially  in  man,  they  have  imdergone 
an  extremely  marked  redviction.     This  reduction  is  at  the  same  time  displayed 


638  SPECIAL  INNERVATIONS 

in  the  peripheral  field  of  olfaction,  by  the  more  restricted  dimensions  of  the 
pituitary  cavity  and  the  holes  of  the  cribriform  j^late  of  the  ethmoid,  and  in  the 
deep  portion  of  the  system,  starting  from  the  olfactory  bulb,  whose  peduncle  is 
reduced  to  a  tract  and  the  roots  diminislied  in  proportion.  Tlie  arrangement  of 
the  limbus  is  marked  in  front  by  the  separation  of  the  two  superior  and  inferior 
arcs,  and  behind  by  a  constriction  in  the  shape  of  an  isthmus  which  forms  a  con- 
necting link  between  the  convolution  of  the  corpus  callosum  and  the  hippocampal 
convolution.  Nevertheless,  the  limbic  convolution  persists  in  its  general  form. 
Olfaction  seems  to  have  taken  refuge  in  the  anterior  portions  (especially  the 
hippocampal  and  that  of  the  cornu  ammonis)  of  the  limbus,  though  we  are  not 
able  to  say  what  functions  have  replaced  it  in  the  remainder  of  its  extent. 

Relations  and  functions  of  the  superior  arc. — The  relationships  least  well 
defined  are  those  connecting  the  superior  arc  (convohition  of  the  corpus  callosvim) 
witli  the  exercise  of  olfaction. 

The  well  developed  root  which  in  osmatics  unites  this  convolution  (internal 
root)  to  the  peduncle,  and  the  much  frailer  one  (of  the  same  name)  which  realizes 
the  same  connexion  in  man,  do  not  allow  of  our  doubting  of  the  participation 
of  the  superior  arc  of  the  limbus  in  the  perception  of  odours. 

The  augmentation  in  voluiue  assumed  by  the  anterior  portion  of  this  arc  in 
osmatics  seems  definitely  to  settle  this  connexion  by  acquainting  us  with  the  fact 
that  the  posterior  portion  is  connected  with  other  functions.  Conversely,  the 
reduction  in  volun:ie  of  this  same  anterior  portion  of  the  supra-callosal  gyrus  in 
primates  (chimpanzee),  proceeding  pari  passu  with  the  reduction  of  the  internal 
root  and  the  relative  maintenance  of  its  posterior  portion,  confirms  the  same 
inference.  In  cetacea  the  regression  terminates  in  the  disappearance  of  the 
internal  root  ;  we  should  expect  to  find  a  parallel  atrophy  of  the  anterior  part 
of  the  supra-callosal  gyrus,  but  this  does  not  appear  to  be  the  case.  This  anterior 
portion  is  the  most  developed,  compared  with  the  rest  of  the  convolution  ;  it  is 
even  traversed  by  furrows  which  increase  its  importance  (Broca). 

We  may  here  observe  a  local  appropriation  by  a  nervous  organ  of  functions 
which  have  not  always  been  its  own  :  but  we  are  totally  ignorant  of  the  nature 
of  these  functions. 

Olfactory  commissure. — If  the  atrophy  resulting  in  the  cerebral  cortex  from 
the  disapjaearance  of  the  internal  and  superior  root  in  cetacea  is  not  indicated  in 
the  limbic  lobe  properly  so  called,  it  is  nevertheless  marked  in  a  neighbouring 
region,  the  orbital  area,  by  an  effacement  of  folds  and  a  smoothness  of  surface 
which  forms  the  commissure  of  Broca. 

4.  Constitution  of  the  olfactory  system 
The  constitution  of  the  olfactory  system  is,  however,  very  difficult 
to  unravel.  As  in  other  sensory  systems,  we  may  distinguish  fibres 
of  projection  and  fibres  of  association.  Between  the  first  and  the 
second  there  is  no  essential  difference.  All  the  elements  of  the  nervous 
system  convey  the  impulse  towards  some  new  element  which  forwards 
it  to  its  destination,  through  a  series  of  progressive  or  regressive  trans- 
formations. All  equally  associate  other  elements  between  themselves 
in  a  common  function  or  one  of  aggregation.  But  the  name  of  fibre 
of  projection  is  more  especially  reserved  for  those  passing  over  great 
distances  and  forming  long  paths,  like  those  which  directly  unite  the 
cortex  of  the  brain  to  the  grey  matter  of  the  spinal  cord,  and  which 
connect  localities  where  this  transformation  presents  very  different 


OLFACTORY  AND  GUSTATORY  INNERVATIONS      639 

values,  in  sometimes  a  descending  and  sometimes  an  ascending  direc- 
tion. The  name  of  fibres  of  association  is  preferably  given  to  those 
which  unite  in  a  transverse  direction  the  fibres  of  projection,  both 
ascending  and  descending,  and  which  complete  the  reflex  or  psychical 
arcs  which  they  constitute,  by  mutually  associating  in  the  brain  its 
gangha,  or  the  grey  axis  of  the  medulla  oblongata  and  of  the  spinal  cord. 


Corp.  quad.   -,-,- 


Tci»n..  seim-circ 


Post.  trij.  T 


Inter ped.  g 


Dent,  body 


Fig.  256. — The  olfactory  system. 
Olfactory  ladiations  and  cerebral  trigon  (after  Dejerine). 

In  every  case  the  two  expressions  have  no  signification  exclusive  the 
one  of  the  other. 

Inferior  or  peripheral  neuron.— By  analogy  with  the  other  specific  systems 
we  recognize  in  the  olfactory  system  a  first  order  of  fibres,  proceeding  from  the 
olfactory  mucous  membrane  to  the  olfactory  bulb  through  the  cribriform  plate 
of  the  ethmoid.  This  is  the  true  olfactory  nerve  analogous  to  a  posterior  root,  or, 
to  put  it  better,  an  auditory  nerve  ;  it  is  formed  of  peripheral  neurons,  whose 
cells  of  origin  have  remained  in  the  mucous  membrane,  and  whose  axon  is  spread 


640 


SPECIAL  INNERVATIONS 


out  in  the  glomeruli  of  the  olfactory  lobe.  There,  these  neurons  enter  into  com- 
munication witli  the  dendrites  of  neurons  of  the  second  order,  formed  by  the 
mitral  cells  whose  axons  are  turned  towards  the  brain,  by  following  the  olfactory 
tract  (or  olfactory  peduncle)  sometimes  so  incorrectly  named  the  olfactory  nerve. 
Olfactory  bulb,  primary  nucleus. — The  olfactory  bulb  is  the  equivalent  of  the 
primary  nuclei  of  the  auditory  nerve  or  of  the  retina  of  the  optic  nerve  ;  it  there- 
fore has  the  value  of  a  primary  nucleus.  The  olfactory  tract  which  starts  from  it 
contains  white  fibres,  which  in  their  turn  proceed  towards  the  cerebral  cortex  : 
these  white  fibres  are  in  part  the  axons  of  the  mitral  cells  (true  fibres  of  jDrojection) 
and  in  part  fibres  arising  from  fresh  cells  disseminated  along  the  tract,  and  which 
receive  the  impulse  by  collaterals  given  off  by  the  axons  of  the  mitral  cells.  We 
here  find  once  more  the  overlapping  of  the  polar  fields,  so  often  pointed  out, 
which  causes  the  impulse  distributed  by  one  neuron  to  reach  several  others,  and 
most  generally  at  unequal  distances. 

The  most  direct  portion  of  the  tract,  that  which  answers  to  its  fibres  of  projec- 
tion properly  so  called,  chiefly  follows  the  external  root,  and  by  it  goes  to  the 
anterior  portion  of  the  hippocampal  convolution,  and  also  to  the  cornu  ammonis. 
Of  moderate  development  in  man  (microsmatic),  the  cornu  ammonis  is  rudi- 
mentary in  the  dolpliin  (anosmatic),  and  highly  developed  in  the  otter  (macros- 
matic).  The  uncus  is  not  prominent  except  in  those  species  in  which  this  horn 
begins  to  retrograde.  The  tract  is  in  strict  developmental  relationship  with  the 
fascia  dentata  or  corps  godronne,  whose  development  it  follows  ;  it  is  also  connected 
with  the  grey  matter  of  the  anterior  perforated  or  quadrilateral  space  of  Broca, 
a  layer  much  atrophied  in  man,  but  which  is  important  in  the  osmatics  and 
manifestly  connected  with  the  sense  of  smell. 

We  have  mentioned  above  that  the  olfactory  tract  contains,  like  the  optic 

nerve,  descending 
or  centrifu gal 
fibres;  fibres 
which  in  other 
terms  bring  back 
the  impulse  to  its 
starting  point  in 
the  olfactory  bulb 
and  to  the  contact 
of  the  mitral  cells. 
This  arrangement 
appears  to  ensure 
a  true  nervous 
circulation  b  e  - 
tween  the  brain 
and  the  olfactory 
bulb,  and  recipro- 
cally. 

Olfactory  chiasma,  anterior  cerebral  commissure. — The  fibres  rising  along  the 
tract  from  its  pyramidal  cells,  take  part  especially  in  the  formation  of  the  middle 
root  and  pass  with  it  into  the  anterior  commissure  to  reach  the  opposite  side. 
They  gain  (at  least  in  part)  the  olfactory  bulb  of  the  opposite  side  and  form  a 
commissxire  with  an  anterior  concavity,  distinct  from  another  interhemispherical 
commissure  with  a  posterior  concavity,  and  equally  distinct  (according  to  some) 
from  fibres  decussated  in  the  manner  of  an  olfactory  chiasma  brought  into  being 
in  this  anterior  commissure.  By  this  path  also  the  olfactory  tract  is  connected 
with  the  optic  thalamus. 

The  gi-ey  matter  of  the  tract  is  an  offshoot  of  that  of  the  hemispheres,  with 


01  f.  bulb. 


0.7.  c»nm. 


Temp,  comin. 


Fig.  257. — AiTangement  of  the  anterior  white  commissure 
(diagram). 


OLFACTORY  AND   GUSTATORY  INNERVATIONS       CAl 

which  it  is  continuous,  and  connected  by  iibres  of  association.  The  siix3erior 
olfactory  root  is  represented  more  especially  by  fibres  of  this  nature  proceeding 
to  the  orbital  convolutions.  But  the  most  remarkable  fibres  of  association  of 
this  system  are  formed  by  the  trigon,  the  nerves  of  Laneisi  and  other  formations 
of  the  same  order. 

Trigon. — The  trigon  is  that  double  circular  tract  (one  on  each  side,  backed  up 
by  its  congener  and  afterwards  divergent)  which,  starting  from  the  mammillary 
bodies,  ascends  by  turning  around  the  optic  thalamus,  redescends  by  pushing 
aside  its  posterior  cokimns,  and  is  continued  by  the  fimbria  which  terminates  in 
the  cornu  ammonis,  whose  relations  with  the  olfactory  bulb  and  its  tract  we 
have  alreadj^  noticed  :  the  fimbria  receives  the  fibres  of  the  fascia  dentata  or 
corps  godronne.  The  sensorial  conduction  is  in  reality  effected  in  a  direction 
converse  to  the  above-mentioned  course,  and  the  impvilses  arrive  at  the  mam- 
millary body  from  the  cornu  ammonis  ;  the  mammillary  body  possesses  numerous 
paths  for  their  distribution.  Some  of  these  paths  pass  through  the  crura  cerebri, 
in  the  neighbourhood  of  the  trochlear  nvicleus  (dorsal  ganglion  of  the  roof  of 
Gudden).  Another  of  them,  under  the  name  of  stripe  of  Vicq  d'Azyr,  ascends 
into  the  anterior  nticleus  of  the  optic  thalamus.  Thence  a  fresh  connexion  with 
the  ganglion  of  the  habenula,  and  from  this  by  a  tract  called  retro-reflex  of 
Meynert,  to  the  interpeduncular  ganglion  of  Gudden,  on  leaving  which  we  are 
in  the  external  motor  or  centrifugal  paths. 

Psalterium. — In  the  interval  between  the  posterior  columns,  the  trigon  shows 
fibres  strung  between  the  pillars  like  the  strings  of  a  lyre.  This  is  an  inter- 
ammonian  commissure  formed  by  fibres  of  the  fimbrise  of  each  side  which 
decussate. 

Olfactory  tract  of  the  cornu  ammonis. — The  trigon,  in  the  anterior  angle  which 
it  forms  with  the  corpus  callosum,  leaves  behind  a  tract  which  is  detached  from 
it,  and  of  which  a  certain  munber  of  fibres  skirt,  in  a  scattered  manner,  the  septum 
luciduni,  pass  in  front  of  the  white  commisstu'e,  and  crossing  the  olfactory  roots, 
with  which  it  has  some  connexion,  contribute  to  form  a  diagonal  tract,  which 
terminates  in  the  hippocampal  convolution.  It  is  from  this  tract  that  the 
perforating  fibres  are  detached  which  rejoin  the  nerves  of  Laneisi  through  the 
corpus  callosum. 

Striae  of  Laneisi. — The  nerves  of  Laneisi  turn  externally  round  the  corpus 
callosum,  which  separates  them  from  the  trigon  and  its  olfactory  tract.  Starting 
from  the  fascia  dentata,  by  the  intermediary  of  the  fasciola  cinerea,  they  form  a 
path  of  association  of  great  length,  which  attaches  these  portions  to  the  olfactory 
area. 

Corona  radiata,  globus  pallidas,  and  optic  thalamus. — The  olfactory  convolu- 
tions (frontal  and  temporsj.1)  have  practically  the  same  general  connexions  as  the 
other  portions  of  the  covering  of  the  cortex  of  the  hemispheres  ;  they  give  off  or 
receive  (or  more  probably,  especially  give  off)  fibres  of  the  corona  radiata.  These 
fibres  establish  a  fresh  connexion  between  these  convolutions  and  the  globus 
pallidus  of  the  lenticular  nucleus,  as  well  as  with  the  thalamus. 

Degenerations. — Gudden  has  applied  his  method  to  the  study  of  this  C£uestion. 
By  shtitting  up  a  nostril  in  a  new-born  rabbit  which  was  killed  after  some  weeks, 
he  established  the  fact  of  an  arrest  of  development  in  the  olfactory  nerves  of  the 
bulb  and  of  the  tract.  Destruction  of  the  olfactory  mucous  membrane  gave 
almost  similar  resvilts.  This  signifies  that  destruction  of  the  primary  neuron 
involves  as  its  consequence  a  certain  amount  of  atrophy  of  the  secondary  neui'ons 
following  it,  from  the  fact  of  privation  of  excitations  and  want  of  functional 
exercise  which  is  its  result  (atrophic  degeneration). 

If  the  olfactory  lobe  be  injured,  the  destruction  then  affects  the  original  cells 
of  a  certain  number  of  deep  cerebral  neurons,  whose  axons  degenerate  as  far  as 

P.  T  T 


642 


SPECIAL  INNERVATIONS 


tlieir  first  relay,  and  at  the  same  time  atrophies  may  occur  in  the  consecutive 
neurons.  These  degenerations,  both  direct  and  consecutive,  have  not  yet  been 
studied  with  the  same  detail  as  those  of  the  other  systems.  Nevertheless,  Tre- 
viranus  had  long  ago  noticed  a  certain  degree  of  atrophy  of  the  cornu  ammonis 
as  a  result  of  lesions  of  the  olfactory  tract.  The  new  methods  confirm  this  obser- 
vation, a  degeneration  may  be  observed  in  the  cornu  ammonis  of  the  same  side, 
and  in  the  pyriform  lobe,  in  the  cornu  ammonis,  and  in  the  olfactory  bulb  of  the 
opposite  side  ;  thus  this  degeneration  reaches  both  crossed  and  direct  fibres. 
There  is  no  degeneration  of  the  root  proceeding  to  the  convolution  of  the  corpus 
callosum  (Loewenthal). 

Caudate  N . 


Fimhru 


'■  Strut,  laeiinarium 


Fi(i.  258. — The  cornu  ammonis  and  tho  fascia  dentata. 

Transverse  diagrammatic  section  ;    fascia  dentata    in    blue  ;    pia  mater  in  red  ;    only   the 
fundamental  elements  are  delineated  ;    partly  after  Dejerine. 


Absence  of  experimental  and  clinical  data. — None  of  the  cortical 
localizations  is  poorer  in  definite  data  (clinical  and  experimental)  capable 
of  checking  the  inductions  of  anatomy  with  regard  to  it.  A  case 
followed  by  autopsy  has  been  observed,  in  which  compression  of  the 
hippocampus  by  a  neoplasm  gave  rise  to  attacks  preceded  by  an  aura 
consisting  in  sensations  of  very  disagreeable  odours.  Besides  being 
isolated,  this  fact  by  itself  is  hardly  demonstrative.     It  is  by  the  defi- 


OLFACTORY  AND  GUSTATORY  INNERVATIONS         643 

ciency  in  function  that  the  sensorial  localizations  are  easiest  to  establish, 
for  functional  exaggeration  may  be  as  well  and  even  better  explained 
by  irritation  at  a  distance  than  by  an  action  directly  localized  on  the 
cortical  region  under  discussion.  A  double  lesion  affecting  the  cortical 
olfactory  area  would  furnish  the  typical  case  required  to  settle  the 
question,  supposing  that  the  anosmia  had  been  verified  during  the 
life  of  the  subject.     Such  a  lesion  must  necessarily  be  very  rare. 

5.  Olfactory  motor  paths 
Motor  activity  is  the  external  measure  of  sensibility.  The  senses 
being  numerous,  the  most  important  amongst  them  will  be  the  one 
having  the  most  habitual  relations  with  motricity,  or,  in  other  words, 
the  one  which  is  the  most  usual  source  of  the  informations  by  the  help 
of  which  ideas  are  elaborated  and  acts  determined.  From  this  point 
of  view  it  is  easy  to  see  how  much  the  sense  of  smell  has  lost  in  us  of 
the  importance  it  possessed  in  the  first  vertebrata  and  still  retains  in 
some  mammals.  In  the  chase,  which  of  old  man  was  forced  to  follow 
to  supply  his  needs,  and  which  now  (amongst  civilized  races)  he  only 
pursues  for  his  pleasure,  he  is  accompanied  by  the  dog,  on  account  of 
its  osmatic  aptitudes.  From  this  example,  it  is  easy  to  see  the  part 
played  by  olfaction  in  the  representations  which  this  animal  makes  for 
itself  of  the  objects  surrounding  it.  Its  brain  is  furnished  with  olfactory 
images  of  an  intensity  and  definite  detail  of  which  our  omu  sense  of 
olfaction  may  give  us  an  idea,  but  of  which  our  sense  of  audition,  for 
example,  is  more  or  less  the  equivalent. 

In  man,  the  olfactory  sense  not  only  no  longer  directs  the  external  motor 
activity,  but  now  plays  only  a  very  incidental  part  therein,  either  with  a  defen- 
sive ami  or  for  the  search  of  the  sensation  itself.  Also  the  motor  activity  directly 
connected  with  olfaction  is  itself  reduced  to  some  movements  of  the  nostrils 
and  of  the  thorax,  co-ordinated  in  the  acts  of  inspiration,  expiration,  or  a  more 
or  less  complete  closing  of  the  respiratory  orifice.  The  facial,  and  with  it  the 
nerves  of  respiration,  are  thus  associated  to  the  olfactory  nerve  in  a  reflex  action, 
which  is,  according  to  circumstances,  defensive  (constriction)  or  adapted  to  the 
exercise  of  smell  (opening  of  the  nostrils  and  inspiration). 

Reflexes  of  adaptation. — In  the  most  elaborated  organs  of  the  senses 
{eye,  ear),  in  addition  to  the  reasoned  and  voluntary  movements  which 
proceed  from  the  activity  of  the  senses,  we  may  observe  reflex  move- 
ments of  adaptation  which  are  of  three  orders  :  (1)  an  external  motricity 
of  direction  ;  (2)  an  internal  motricity  of  adaptation  ;  (3)  vaso-motor 
and  secretory  activities  which  are  equally  necessary. 

a.  External  adaptation. — In  the  movement  of  the  nostrils  (and  that  of 
the  thorax)  we  observe,  almost  exactly,  the  action  of  the  directing 
muscles  of  the  eye  or  of  the  external  ear.     We  do  not  know  of  any 

r,  TT 


644  SPECIAL  INNERVATIONS 

internal  muscle  in  the  nostril  having  a  function  similar  to  the  iris  and 
the  ciliary  muscle,  or  to  the  muscles  of  the  ossicles  in  the  middle  ear  ; 
but  secretory  epithelia  regulate  the  state  of  humidity  suitable  for  the 
impression  of  odours  on  the  olfactory  mucous  membrane,  and  vaso- 
motor actions  also  regulate  the  circulation  in  this  mucous  membrane, 
b.  Internal  adaptation . — As  far  as  can  be  judged  from  what  takes 
place  at  the  entrance  and  the  inferior  portion  of  the  nostril,  the  vaso- 
motor and  secretory  innervation  of  the  organ  of  olfaction  closely  imitates 
that  of  the  visual  and  auditory  organs.     The  great  sympathetic  by 
means  of  fibres  proceeding  from  the  thoracic  spinal  cord,  and  by  others 
which,  originally  contained  in  the  trunk  of  the  trigeminal  converge 
with  the  preceding  ones  towards  the  spheno-palatine  ganglion,  balances 
the  circulation  of  this  region,  moderates  it  by  its  constrictors,  and 
exaggerates  it  by  its  dilators,  which  sometimes  come  from  the  cervical 
sympathetic,  and  sometimes  from  the  trigeminal,  and  which  are  in  both 
nerves  very  excitable  in  the  dog.     The  system  of  the  secretory  nerves 
has  probably  the  same  topography  and  the  same  functional  duality. 

Relations  to  general  sensibility. — We  may  repeat  for  the  sense  of  olfaction 
what  has  already  been  remarked  with  regard  to  the  other  senses,  concerning 
their  relations  with  general  sensibility.  The  olfactory  mucous  membrane,  the 
peripheral  organ  of  the  sense  of  smell,  possesses  special  nerves  for  odours  :  it  also 
possesses  others  which  here  represent  tactile  sensibility,  this  latter  having  uni- 
versally devolved  upon  the  organs,  is  for  this  reason  called  general.  The  tri- 
geminal ensures  this  general  sensibility  for  the  interior  as  well  as  the  exterior 
of  the  nostril.  Its  paralysis  (of  functional  or  traumatic  natvire),  hysteria,  section 
of  the  nerve)  causes,  in  addition  to  loss  of  general  sensibility,  a  dist\arbance  or 
even  a  paralysis  of  olfaction.  These  facts,  clearly  grasped  by  Magendie,  would 
thus  give  rise  to  a  belief  in  the  direct  participation  of  the  trigeminal  in  the  osmatic 
function. 

Sensorial  paralysis  is  here  (as  it  is  for  sight  and  hearing)  a  secondary  pheno- 
menon. It  does  not  immediately  follow  experimental  section  of  the  sensory 
nerve  (trigeminal),  but  is  the  consequence  of  the  disturbances  of  nutrition  resulting 
from  it.  The  explanation  of  these  nutritive  disttirbances  has  often  varied.  The 
fact  that  they  succeed  the  paralysis  of  an  obviously  sensory  nerve  causes  them 
to  be  attributed  to  a  disappearance  of  general  sensibility,  which  would  be  the 
immediate  and  sufficient  cause.  We  believe  in  the  existence  of  centrifugal 
nerves  governing  the  proper  functions  (and,  by  the  medium  of  these,  the  nutrition) 
of  the  fixed  elements  of  the  mucous  membrane,  which  elements  degenerate  as  a 
result  of  section  of  their  own  nerves,  as  do  all  organs  no  longer  receiving  stimula- 
tion. 

B.  GUSTATORY  SYSTEM 
1.  Field  of  impressions. — The  field  of  gustatory  impressions  is  limited 
to  certain  regions  of  the  buccal  mucous  membrane  ;  namely  :  (1)  the 
base  of  the  tongue  behind  the  lingual  V  ;  (2)  its  tip  and  slightly  also 
its  borders  ;  (3)  the  borders  of  the  soft  palate.  These  limits,  however, 
may  vary  in  individuals. 


OLFACTORY  AND  GUSTATORY  INNERVATIONS        645 

Papillae  of  the  tongue. — It  is  especially  at  the  base  of  the  tongue 
that  the  receptive  organs  of  gustatory  impressions  have  chiefly  been 
studied.  The  mucous  membrane  is  provided  with  papillae  of  various 
forms  [filiform,  fungiform,  caliciform).  The  organs  of  taste  are  buds 
disseminated  on  the  fungiform  and  more  especially  on  the  caliciform 
papillae,  on  the  borders  of  the  circumvallate  fossa  surrounding  these 
papillae,  which  would  be  better  named  calicicoles,  since  they  arise  in 
the  interior  of  the  calyx  instead  of  forming  it  (M.  Duval). 


Taste  buds. — The  taste  bvids  are  small  ovoid  organs,  whose  long  axis  is  directed 
perpendicularly  to  the  surface  of  the  mucous  membrane.  They  appear  to  be 
striated  on  their  surface,  and  these  striae  correspond  to  elongated  cells  following 
the  meridians  parallel  to  the  long  axis. 

Gustatory  cells. — These  cells  are  of  two  kinds  :  some  are  supporting  elements  ; 
others  specifically  differentiated  elements,  adapted  to  the  reception  of  the  gusta- 
tory impression  [gustatory  cells).  The  first  exist  on  the  whole  circumference  of  the 
taste  bud,  and  also  in  its  interior.  It  is  amongst  them  that  the  second  are  found  ; 
their  form  is  that  of  a  nucleated  element  prolonged  on  one  side  by  a  ciliated  rod 
which  has  an  outlet  outside  the  taste  bud,  and  on  the  other  by  a  thin  fibre  which 
is  directed  towards  the  deep  surface  of  the  mucous  membrane.     The  gustatory 

taste  bud  is  fvu-nished  with  a  kind  of  pore,  situated 
in  the  suj^erficial  prolongation  of  its  axis.  By  this 
pore  the  ciliated  prolongations  of  the  gustatory 
cells  emerge,  which  are  thus  bathed  in  the  buccal 
liquid  containing  sapid  substances. 

Equivalency. — The  gustatory  cells  are  not  the 
equivalent  of  the  olfactory  cells  ;  they  are  not 
nervous  elements.     They  are  only   in  immediate 


Pig.     259. — Foliated    gustatory  Fig.   260. — Receptive  gustatory  nervovis  arboriza- 

apparatus  of  the  rabbit.  tions. 

p,  taste  pore  ;   s,  gustatory  cells  ;  A,  taste  bud  with  a  gustatory  cell  surrounded  by  nerve 

i,    intra- epithelial  nervous    fibres  ;  ramifications  :   B,   the  ramifications  are  alone  indicated 

n,  afferent  nerve  of  the  taste  bud  (after  M.  Duval). 
Rafter  Ranvier). 

contact  with  the  arborizations  of  the  nerves  of  taste,  whose  ganglionic  cells 
are  situated  in  the  ganglion  of  Andersh  as  regards  the  glosso-pharyngeal.  The 
initial  extremities  of  these  nerves  penetrate  into  the  taste  buds  by  intrageminal 
fibrillse  and  cover  the  gustatory  cells  with  their  arborization.  They  thus  receive 
the  exciting  shock  of  the  sapid  substances  at  second  hand,  through  the  medium 
of  the  gustatory  cells,  just  as  the  acoustic  nerves,  the  nerves  of  touch,  and  the 
bipolar  cells  of  the  retina  receive  it  from  analogous  cells. 

Section  of  the  glosso-pharyngeal  nerve  involves  degeneration  of  the  nervous 


646  SPECIAL  INNERVATIONS 

arborisations,  and  secondarily,  disajapearance  of  the  gustatory  cells,  and  atrophy 
of  the  taste  buds  (Kanvier). 

2.  Nerves  of  taste. — The  base  of  the  tongue  has  the  glosso-pharyngeal 
for  a  sensorial  nerve  ;  the  tip  has,  through  the  medium  of  the  Hngual, 
the  chorda  tympani,  and  the  pillars  of  the  palate  have  the  filaments  of 
the  palatine  nerves.  These  latter,  and  also  the  chorda,  arise  from  the 
nerve  of  Wrisberg  or  small  root  (sensorial  root)  of  the  facial.  The 
primary  nucleus  of  the  glosso-pharyngeal  nerve  and  that  of  the  nerve 
of  Wrisberg  approximate  each  other  in  the  substance  of  the  medulla 
oblongata  (M.  Duval). 

Relations  to  general  sensibility. — These  are  very  visible  and  anato- 
mically well  marked  in  the  gustatory  apparatus.  The  area  of  gustatory 
impressions  is  sensible  to  those  of  touch  and  of  temperature,  and  pos- 
sesses tactile  as  well  as  gustatory  nerves.  These  elements  of  different 
modes  of  sensation  are  mixed  in  the  nerve  trunks  of  the  tongue  and  of 
the  soft  palate  ;  the  glosso-pharyngeal  and  the  chorda  tympani  respond 
to  mechanical  excitation.  In  the  glosso-pharyngeal  the  sensorial  and 
sensory  elements  are  mixed  at  starting  from  the  origins  of  the  nerve, 
though  they  are  sorted  out  in  the  bulb  into  distinct  nuclei  ;  the  elements 
of  special  sensibility  jDroceed  to  the  chorda  by  the  nerve  of  Wrisberg  ; 
those  of  general  sensibility  appear  to  come  to  it  from  the  trigeminal 
(perhaps  by  the  petrosal  nerves).  Both  of  these  being  enlarged  by 
centrifugal  vaso-motor,  and  secretory  elements  which  also  pass  by  the 
nerve  of  Wrisberg,  proceed  to  throw  themselves  into  the  trunk  of  the 
lingual  (branch  of  the  inferior  maxillary  nerve,  itself  a  branch  of  the 
trigeminal)  which  bestows  general  sensibility  on  all  the  anterior  portion 
of  the  tongue. 

Secondary  disturbances. — The  dissociation  of  general  gustatory 
sensibility  is  then  only  possible  for  the  anterior  portion,  or  tip,  of  the 
tongue,  by  cutting  in  an  isolated  manner  the  chorda  tympani  or  the 
trigeminal  in  the  skull.  The  resulting  secondary  disturbances  of  vas- 
cularization, secretion,  and  nutrition  have  often  embarrassed  the 
experimenters  who  have  attempted  to  effect  this  dissociation.  There 
are,  however,  facts  sufiEiciently  convincing  to  lead  us  to  accept  it  in 
principle. 

Unknown  cortical  localization. — With  regard  to  the  cortical  localization  of 
the  sense  of  taste,  we  have  no  data,  either  observational  or  experimental  ;  further, 
on  this  matter,  morphological  inductions  are  wanting.  Neither  the  study  of 
myelination  nor  any  anatomical  method  furnishes  us  with  any  indications  which 
are  in  the  least  probable  as  concerns  the  locality  of  the  cortex  which  is  connected 
with  the  nuclei  of  the  glosso-pharyngeal  nerve  or  that  of  Wrisberg.  There  is. 
hesitation  in  connecting  the  gustatory  area  with  the  tactile  region  (as  some  do),, 
or  with  the  olfactory  or  an  intermediate  area  (as  do  others). 


OLFACTORY  AND  GUSTATORY  INNERVATIONS       647 

3.  Reflexes   of  adaptation. — As   a   set-off  we   are  acquainted  with 
reflexes  of  adaptation  obviously  appertaining  to  the  exercise  of  the 
function  of  taste.     The  movements  of  the  tongue  are  controlled  by 
the  hypoglossal  nerve,  whose  nucleus  adjoins  that  of  the  glosso-pharyn- 
geal.     Further,  taste  is  connected  with  the  act  of  mastication,  of  which 
act  the  motor  nerves  are  also  of  bulbar  origin.     In  addition  to  these 
strictly  motor  actions,  taste,  in  a  manner  which  is  also  reflex,  involves 
vaso-motor  and  secretory  modifications,  the  nervous  mechanism  of 
which  is  well  known.     It  is  contained  in  the  great  sympathetic  and 
its    bulbar   dependencies.      The    vaso-constrictors    ascend   from    the 
thoracic  spinal  cord  through  the  cervical  cord  ;    the  dilators  proceed 
to  the  lingual  mucous  membrane  through  the  glosso-pharyngeal  and 
the  chorda  tympani,  to  the  soft  palate  through  the  palatine  nerves  ; 
these  latter,  and  also  those  of  the  chorda  tympani,  arise  from  the  nerve 
of  Wrisberg.     These  vaso-dilatory  elements  are  duplicated  by  secretory 
elements  having  the  same  origin,  which,  through  the  glosso-pharyngeal, 
proceed  to  the  parotid  gland,  by  the  chorda  tympani  to  the  sub-maxil- 
lary and  to  the  sub-lingual  glands,  and  by  the  palatine  nerves  to  the 
glands  of  the  mucous  membrane  of  the  soft  palate.     The  vaso-dilation 
proceeds  }ja7~i  passu  with  the  secretion  of  the  glands,  and  the  two  pheno- 
mena are  favourable,  indeed  indispensable,  to  the  exercise  of  the  sense 
of  taste,  sapid  impressions  only  arising  in  suitably  vascularized  and 
moistened  mucous  membrane.     The  sensorial  impression  excites,    by 
reflex  action,  the  phenomena' of  vascularization  and  of  secretion,  by 
the  help  of  a  cycle  of  adaptation,  similar  to  that  existing  in  all  the 
other  organs  of  the  senses. 

Painful  reflex. — The  secretion  which  is  the  most  directly  connected  with  the 
sense  of  taste  appears  to  be  that  of  the  sub-maxillary  and  of  the  sub-lingual 
glands.  The  parotid  secretion,  more  watery  and  abvmdant  in  certain  animals 
(herbivora),  seems  to  be  especially  connected  with  mastication  (CI.  Bernard). 
The  reflex  secretion  of  -the  sub-inaxillary  gland  may  be  easily  provoked,  by 
stimulating,  in  animals,  the  central  end  of  the  cut  lingual  nerve.  Although  the 
lingual  contains  gustatory  fibres  (coming  to  it  through  the  chorda  tympani), 
this  secretion  must  not  be  considered  as  resulting  from  a  stimlus  of  a  purely 
sensorial  nature  reflected  to  the  gland.  The  lingual,  a  branch  of  the  trigeminal, 
contains  chiefly  elements  of  general  sensibility,  and  the  abundant  flow  of  saliva 
following  its  centripetal  stimulation  is  the  expression  of  an  ordinary  reflex  accom- 
panied by  pain.  It  is  this  reflex  salivation  which  may  be  observed  in  dental 
neuralgia,  or  in  other  varieties  of  neuralgia  of  the  trigeminal. 


CHAPTER    V 
LANGUAGE    AND    IDEATION 

Language  is  a  succession  of  motor  acts  wliich^by  their  combinations, 
usually  express  ideas. 

A  distinction  is  made  between  articulated  and  sjjokeyi  language, 
which  makes  use  of  sounds  (audible  signs),  and  a  written  language, 
which  employs  letters  (visible  signs).  Language  is  the  great  charac- 
teristic of  humanity,  and  it  forms  the  basis  of  civilized  life.  It  is  the 
facultas  sigyiatrix  of  Kant. 

Emotional  expressions.^ — Below  the  language  of  ideas,  a  language  of  the  emotions 
exists.  Every  emotion  is  revealed  by  a  series  of  motor  acts  which  are  both 
internal  and  external.  The  latter,  which  may  be  reduced  to  mere  attitudes, 
reveal  to  others  the  j)assions  which  agitate  us.  Having  a  deeper  root,  this 
language  is  much  more  general  than  the  preceding  ;  it  is  indeed  both  universal 
and  natural  ;  animals  comprehend  it,  and  by  its  aid  they  communicate  with 
each  other  and  with  us.  Darwin  has  endeavoured  to  find  in  the  structixre  of 
language  a  support  for  his  theory  of  evolution.  It  is  reasonable  to  suppose  that 
the  conventional  language  of  the  different  human  races  is  derived  from  the 
language  expressive  of  the  emotions,  this  being  common  both  to  man  and  to 
animals  ;  but  it  must  be  recognized  that  the  traces  of  transition  between  one 
and  the  other  are  at  present  entirely  lost  or  inappreciable. 

A.  FORMATION  OF  WORDS  AND  IDEAS 
Language  is  expressed  by  signs  which,  being  associated,  form  ivords  ; 
words  express  ideas  ;  ideas  arise  in  us  from  sensations,  and  sensations 
proceed  from  i?npressions  made  upon  us  by  the  external  world.  Such 
is  the  filiation  of  the  phenomena.  They  are  displayed  in  a  nervous 
cycle  of  great  complexity,  and  their  mode  of  succession  is  naturally 
opposed  to  the  above-mentioned  filiation ;  that  is  to  say,  it  proceeds 
from  the  impression  to  the  motor  act.  We  find,  once  again,  in  the 
function  of  speech  that  connexion  between  sensation  and  movement 
which  underlies  all  nervous  functions,  and  it  is  here  presented  under 
multiple  forms  ;  we  also  observe  in  it  both  consciousness  and  uncon- 
sciousness, with  their  unequal  and  variable  distribution.  Most  of 
the  nervous  mechanisms  so  far  studied  are  disj)layed  in  it  in  a 
condensed  condition.  Further,  it  often  fuses  into  a  single  act  two,  or 
even  three,  of  the  principal  specific  systems  which  share  the  cerebral 


LANGUAGE  AND  IDEATION  64& 

cortex  between  them.  This  function  of  language  is  pre-eminently 
adapted  for  furnishing  a  conception  of  the  function  of  the  brain  as  a 
whole. 

1.     Representations  in  consciousness 

1.  Method  of  analysis. — Language  is  one  of  the  superior  functions 
of  the  nervous  system  ;  on  this  account  it  is  amenable  to  a  double 
analysis,  one  purely  internal  or  subjective,  performed  on  ourselves,  the 
other  objective  and  external;  conducted  according  to  physiological 
methods. 

Physical  world  and  moral  world. — For  each  of  us  there  is  an  external 
ivorld,  opened  out  to  us  by  our  senses,  and  an  internal  tcorld,  which  is 
more  especially  realized  when  we  close  the  senses  to  impressions  from 
without.  The  first  is  the  ijhysical  world,  the  second  the  psychical  or 
moral  world.  The  first  is  formed  of  objects  and  phenomena  which  we 
discern  by  our  senses,  but  indirectly,  inasmuch  as  it  is  external  to  us  ; 
the  second  is  formed  of  moral  representations  or  phenomena  ;  and  this 
we  comprehend  directly,  because  it  is  internal  to  us. 

The  jahysical  and  jDsychical  worlds  are,  by  their  nature,  incapable  of 
reduction  to  a  common  element.  Every  attempt  to  bring  them  back 
to  a  uhity  which  may  probably  exist  at  the  foundation  of  things,  but 
for  the  perception  of  which  our  position  is  unfavourable,  fails  before  the 
arguments  of  evidence  and  of  common  sense.  Nevertheless,  we  feel 
the  strict  connexion  and  dependence  in  which  they  exist  with  regard 
to  each  other.  Further,  between  the  operations  performed  within  us 
on  representations,  and  those  effected  external  to  us  on  objects  and 
movements,  we  detect  an  analogy  which  ordinary  language  sanctions 
by  expressing  them  in  similar  terms.  Internally,  as  well  as  externally, 
to  ourselves,  we  recognize  amplifications  and  reductions,  sef)arations 
and  reunions,  concordances  and  oppositions,  actions  and  reactions, 
etc. 

Internal  and  external  observation. — When  we  carry  out  an  analysis 
of  this  nature,  on  the  one  hand  in  our  owai  consciousness,  and  on  the 
other  hand  with  regard  to  the  brain  of  a  fellow  creature  considered  as 
an  external  object,  we  apply  the  two  methods  to  the  study  of  a  question 
fundamentally  one  and  indivisible  regarded  from  two  opposite  aspects, 
and  each  method  is  almost  useless  alone.  Consciously  or  imcon- 
sciously,  we  call  upon  them  to  lend  each  other  a  mutual  support.  It 
is  not  difficult  to  discover  that  the  two  analyses  thus  conducted,  the 
one  in  the  moral  and  the  other  in  the  physical  world,  though  they  may 
not  be  far  advanced  as  regards  actual  results,  are  not  superposed  in 
the  things  with  which  they  are  concerned.     The  method  by  which  we 


650  SPECIAL  INNERVATIONS 

take  cognizance,  with  our  senses,  of  objects  external  to  ourselves  is  more 
particularly  an  analytical  one.  It  furnishes  us  as  concerns  the  brain  of  a 
fellow  creature  (and,  therefore,  also  our  own)  with  details  which  our 
internal  vision  can  in  no  way  grasp.  Concerning  the  static  organization 
of  the  elements  it  has  thus  discovered,  it  possesses  and  continually 
acquires  data  which  are  not  without  importance,  but  which  will  really 
bear  fruit  only  Avhen  the  day  arrives  in  which  it  will  see  this  dead 
matter  in  a  state  of  movement  and  can  then  comprehend  the  incessant 
modifications  which  constitute  its  dynamic  state. 

Our  internal  sense  also  discerns  representations  ;  but,  amongst 
these  representations,  precisely  those  of  the  material  objects  (brain 
and  its  component  elements)  presiding  over  its  activity  and  its  existence 
are  effaced.  The  simplest  of  these  representations  (the  sensations), 
those  which  enter  as  elements  into  the  psychical  aggregations  which 
minister  to  the  operations  of  the  mind,  those  beneath  which  the  internal 
sense  no  longer  analyses  or  distinguishes  anything,  are  physically 
brought  about  by  a  physiological  complexus  of  a  very  elevated  organiza- 
tion (cerebral  cortex),  of  which  it  can  grasp  neither  the  elements  nor  the 
limits.  The  play  of  the  nervous  forces,  on  which  it  depends,  while  at 
the  same  time  directing  it,  eludes  it  in  the  same  way  as  do  all  material 
objects  and  phenomena.  Should  this  play  of  forces,  however,  become 
accessible  to  it,  it  will  be  so  by  means  of  a  detour  ;  that  is  to  say,  by 
passing  once  more  through  the  external  senses,  which  will  then  provide 
it  with  its  representation  and  nothing  but  its  representation. 

Thus  it  is  necessary  for  us  to  watch  over  ourselves  alternately  with 
our  eyes,  with  our  reason.  We  are  acquainted  with  the  fact  that  the 
two  analyses,  although  following  parallel  paths,  do  not  overlap  each 
other.  We  shall  rarely  call  upon  them  to  verify  each  other.  We 
rather,  by  taking  each  in  its  own  sphere  of  action,  seek  to  complete 
one  by  the  other. 

2.  Multiple  operations  of  the  mind. — Internal  observation  shows  us 
a  distinct  series  of  operations  in  ourselves,  to  which  ordinary  language 
has  given  different  names. 

Sensation,  knoivledge,  recog^iition  (psychological),  representation, 
memory,  attention,  idea,  ivill,  are  all  internal  phenomena  (eluding  the 
external  senses)  which  every  one  can  distinguish  from  each  other,  and 
the  relations  and  connexions  of  which  we  are  able  to  recognize. 

Primordial  element,  sensation. — Of  all  these  phenomena,  sensation 
is  the  most  elementary.  This  is  the  original  fact  whence  all  others 
are  derived  by  extensions,  associations,  dissociations  or  different 
combinations.  In  itself  it  is  simpler  than  it  appears  to  be.  A  sensa- 
tion may  be  isolated  from  every  other  to  such  a  degree  as  to  leave  no 


LANGUAGE  AND  IDEATION  651 

trace  behind  it.  The  sensations  revealed  by  the' cries  of  an  individual 
under  the  influence  of  chloroform,  and  which,  on  awakening  from  this 
influence,  he  forgets,  are  of  this  nature  ;  those  which  first  penetrate 
into  the  nervous  system  of  the  new-born  child  are  of  the  same  order  ; 
they  are  independent  elements,  not  united  between  themselves.  We 
must  not  forget  that  sensation  is  a  physiological  complexus  ;  it  requires 
for  its  development  a  highly  elaborated  system  of  neurons  which  receive 
at  its  origin  an  impression  from  the  external  world  ;  but,  for  our  in- 
ternal sense,  sensation  is  pre-eminently  the  psychical  element. 

Its  residuum. — An  impression,  by  being  itself  renewed  and  by  renew- 
ing the  sensation,  forms  habitual  paths  for  itself  in  the  nervous  system. 
Not  only  does  it  create  its  oivn  paths,  ivJiich  cause  it  to  have  in  this  system 
always  the  savne  reverberation,  but  it  continues  permanently  in  them.  All 
sensation  leaves  behind  it  what  is  known  as  a  residuum.  I,  for  my 
part,  consider  that  this  permanence  has  for  its  physical  condition  a 
circulation  of  the  impulse  in  the  interior  of  closed  cycles,  which  renew 
it  automatically  in  an  indefinite  manuer. 

Strong  and  weak  state.^The  impression,  attacking  at  the  periphery 
a  sj^stem  which  has  already  been  subjected  to  anterior  impressions, 
would  then  be  no  longer  in  the  condition  of  an  impression  which  was 
the  first  to  fall  into  this  system.  It  becomes  associated  with  the 
residues  left  by  antecedent  impressions  ;  it  is  continuous  with  the 
latter  in  time.  From  the  tceak  condition  into  which  they  had  fallen, 
it  brings  them  back  once  more  to  a  strong  condition.  It  synthetizes  and 
identifies  itself  "\\4th  them.  And  hence  it  follows  that  we  are  not,  so 
to  say,  conscious  (except  by  an  artifice  of  reasoning)  of  a  simple  sensa- 
tion, but  only  of  one  which  is  prolonged  or  renewed. 

Memory. — This  phenomenon  of  synthesis  in  time  is  called  memory. 
Forasmuch  as  it  identifies  a  freshly  produced  sensation  with  one 
pre\aously  experienced,  it  is  recollection .  Forasmuch  as  it  enlightens 
us  with  regard  to  the  original  cause  of  the  impression  and  sensation,  it 
is  knowledge.  And  forasmuch  as  it  associates  together  all  this  know- 
ledge of  different  forms,  and  derived  from  varied  sources,  according 
to  a  logical  classification,  it  is  acquired  experience.  All  these  data  of 
internal  observation  are  self-evident. 

Consciousness. — They  are  self-evident  because  they  are  illuminated 
by  that  internal  radiance  which  we  call  consciousness  :  with  the  excep- 
tion of  residual  sensation,  which  escapes  it.  In  the  time  Avhich  separates 
the  first  or  anterior  from  the  renewed  sensation,  there  is  a  passing  over 
from  consciousness  to  unconsciousness  ;  then,  when  the  renewal  takes 
place,  a  converse  passage  from  unconsciousness  to  consciousness.  Con- 
sciousness is  susceptible  of  degree,  and  its  variations  and  gradations 


iW2  SPECIAL  INNERVATIONS 

are  infinite  ;  these  gradations  Ave  may  observe  in  ourselves,  until  it 
reaches  that  threshold  below  which  it  practically  disappears.  On  the 
other  hand,  physiological  facts  prove  that,  when  sensation  is  no  longer 
obvious  to  us,  it  yet  survives  in  its  physical  conditions.  The  conscious 
and  the  unconscious  reflex  arcs  are  formed  in  the  image  the  one  of  the 
other. 

Forms  of  sensation. — Like  the  systems  presiding  over  them,  sensa- 
tions are  of  different  modalities  (sight,  hearing,  touch,  etc.).  The 
combinations  of  the  impressions  from  Avhich  they  arise  are  also  different : 
this  is  what  is  called  the  forin  of  the  sensation.  By  dint  of  being  re- 
peated in  us,  as  the  result  of  similar  impressions,  the  sensations  assume 
a  signification,  a  determinate  symbolism  ;  this  is  what  is  called,  in  the 
language  of  the  schools,  the  coyitent  of  the  sensation.  The  content  is 
the  object,  the  thing  in  harmony  with  the  sensation. 

Representations  ;  psychical  images. — By  these  mechanisms,  some 
connecting  sensations  in  time  and  others  simultaneously  demonstrating 
to  us  the  varied  qualities  of  objects,  a  representation  of  the  external 
world  is  established  in  us  :  this  is  the  aggregation  of  our  psychical 
images.  These  images  are  classed,  arranged,  systematized  in  the  un- 
conscious, and  they  may  be  evoked  at  each  impression  of  the  object 
to  which  they  correspond  ;  that  is  to  say,  at  each  sensation  recalled 
by  it. 

3.  Analysis  and  synthesis  ;  formation  of  the  images  of  objects. — 
Each  sense,  each  sensation,  enables  us  to  know  and  to  recognize  only 
one  quality  of  the  objects  which  have  made  an  impression  on  it.  The 
mind,  the  cerebral  activity,  and  the  thoughts  are  employed  in  separat- 
ing and  abstracting  the  similar  qualities  of  different  objects,  and  attach- 
ing them  to  the  object  which  possesses  them  all  together.  By  this 
new  operation  of  the  mind,  recognition  of  the  sensations  leads  to  recog- 
nition of  the  objects.  To  refer  once  more  to  Charcot's  example,  so 
often  quoted,  a  clock  may  be  heard,  seen  and  touched.  The  mind 
connects  so  intimately  the  forms  of  the  three  sensations  reaching  it 
from  the  object  "  clock,"  that,  at  each  new  impression  proceeding 
from  this  object  to  one  of  the  three  senses  (vision,  hearing  or  touch),  the 
latter  is  at  once  recognized.  One  impression  alone  is  sufficient  to  give 
rise  to  the  three  sensations,  one  impression  being  very  strongly  and  the 
two  others  but  feebly  marked  ;  the  idea  of  the  object  springs  from 
this  association. 

This  is  thought  in  its  most  lowly  aspect,  and  in  this  form  it 
appertains  both  to  man  and  to  animals.  By  means  of  its  associated 
sensations,  the  animal  elaborates  ideas  which,  presenting  the  most 
•elementary  degree  of  generality,  are  capable  of  so  directing  its  acts  as 


LANGUAGE  AND  IDEATION  653 

to  ensure  self-preservation.  In  this  way  a  foundation  of  concrete  ideas 
is  effected. 

Thought,  abstraction. — But  "  thought  "  in  the  ordinary  sense  of  the 
word,  implies  a  process  of  separation  and  re-composition,  or,  properly 
speaking,  of  abstraction,  which  is  carried  much  farther,  and  in  a  great 
degree  distinguishes  human  thought  from  that  of  animals.  The 
animal,  as  we  have  just  said,  thinks  by  means  of  its  sensations  ;  man 
thinks  %\dth  abstract  ideas,  that  is  to  say,  with  words.  By  a  new  process 
of  internal  analysis  working  on  psychical  images,  he  elaborates  a  col- 
lection of  verbal  images  whose  symbolism  is  far  more  exalted  than  is 
that  formed  by  his  images  of  objects.  This  is  language  heard  and 
spoken,  to  which  civilized  man  adds  language  read  and  written. 

Formation  of  verbal  images. — To  return  to  the  preceding  example. 
The  word  clock  when  first  heard  by  the  child  does  not  awaken  in  him 
the  image  of  the  object  "  clock,"  nor,  indeed,  that  of  any  kno^\^l  object  ; 
at  first  it  only  tends  to  create,  and  in  fact  creates,  a  new  auditory  image, 
neither  more  nor  less  important  than  those  he  already  possesses.  But 
this  auditory  image,  if  evoked  in  determinate  and  suitably  chosen 
circumstances,  gives  rise  in  him  to  a  new  process  of  abstraction,  carried 
much  farther  than  the  preceding,  by  means  of  which  it  acquires  a  sym- 
bolical value  of  a  truh^  general  order.  The  instinctive  operation  by 
means  of  which  the  child's  brain  acquires  this  new  faculty  is  one  of  the 
same  nature  as  those  taking  part  in  the  reasoning  faculty,  such  as  it  is 
methodically  exercised,  according  to  logical  laws,  in  the  adult. 

Reason  is  the  faculty  possessed  by  the  human  mind  of  performing 
such  operations.  Further,  it  is  by  the  superposition,  no  longer  simply 
of  psychical  images,  but  of  concrete  ideas  formed  by  the  superposition 
of  these  images,  that  the  mind,  proceeding  from  abstraction  to  abstrac- 
tion, at  last  attains  to  the  acquirement  of  general  ideas,  abstract  con- 
ceptions, properly  so  called. 

Comparison. — Comparison  always  arises  from  a  superposition  of 
two  things,  having  points  of  resemblance  in  common  ;  and,  again,  this 
process  of  superposition  emphasizes  the  features  displayed  in  common 
and  eliminates  those  of  difference.  All  comparison  is  an  internal 
experiment  of  identification  of  sensations  and  ideas  ;  this  experiment 
being  followed  or  not  by  an  anticipated  result,  but  in  either  case  having 
its  own  significance.  The  immense  advantage  possessed  by  the  superior 
animals  over  their  inferior  brethren,  and  of  man  over  animals,  is  that, 
by  means  of  sensations  and  ideas,  they  can  perform  those  experiments 
which  the  uncultivated  or  irrational  creature  is  forced  to  bring  about 
by  the  help  of  its  motor  powers.  From  this  results  an  enormous 
economy  of  time  and  strength. 


654  SPECIAL  INNERVATIONS 

Thus  the  infant  accumulates  a  collection  of  verbal  auditory  images. 
By  means  of  a  fundamentally  similar  mechanism  there  will  be  formed 
later  on  a  collection  of  verbal  visual  images.  The  process  by  which  the 
latter  are  acquired  is  more  obviously  analytical  merely  because  the 
capabilities  of  the  subject  are  then  more  developed,  and,  the  faculty  of 
spoken  language  being  acquired,  this  aids  in  the  acquisition  of  the 
written  language. 

2.     Motor  actions  of  written  and  spoken  language 

In  spoken  or  written  language  the  complement  of  the  sensorial  or 
intellectual  operations  is  represented  by  motor  acts,  and  these  enable 
us  to  reproduce  externally  those  audible  or  visible  signs  which  have 
made  an  impression  on  our  own  senses,  so  that  they  may  make  a  similar 
impression  on  the  senses  of  our  fellow  creatures.  It  is  this  exchange 
of  symbolical  signs,  rendering  feasible  an  exchange  of  ideas,  which 
places  the  function  of  language  in  the  highest  rank  amongst  the  func- 
tions which  are  described  as  those  of  external  relation.  As  in  all  the 
functional  systems,  the  deveIop7nent  of  the  sensory  or  sensorial  precedes 
that  of  the  corresponding  motor  aptitude.  The  articulation  of  sounds 
in  the  child  follows  more  or  less  closely  on  the  acquisition  of  either 
simple  or  verbal  auditory  images  ;  further,  from  the  very  first  moment 
in  which  it  becomes  possible  for  it  to  do  so,  it  aids  and  singularly  accele- 
rates this  acquisition.  Writing  also  follows  reading,  so  soon  as  the 
child  acquires  the  first  rudiments  of  the  art.  The  motor  acts  of  written 
language  are,  however,  when  required,  at  the  service  of  auditory  images, 
and  articulated  speech  may  also  aid  in  the  interpretation  of  the  visual 
images  of  written  language.  It  is  possible  to  answer  a  verbal  question 
in  writing,  and  also  possible  to  reply  to  a  written  question  verbally. 

Spoken  language  possesses  the  advantages  of  facility  and  prompti- 
tude ;  it  serves  for  the  everyday  exchange  of  ideas.  Written  language 
is  more  artificial  ;  the  pen  and  the  book  are  factitious  organs  interposed 
between  those  conversing  ;  but  it  has  the  advantage  of  the  permanence 
of  the  written  signs  and  of  the  possibility  of  multiplying  them  indefi- 
nitely by  printing  ;  it  also  points  to  an  essential  progress  in  human 
culture. 

Deaf-mutism. — In  those  deaf  from  birth  speech  also  is  wanting  ;  this  is  the 
result,  not  of  a  motor  paralysis  of  the  organs  of  phonation,  but  of  the  absence 
of  auditory  sensations.  It  is  to  the  imitation  of  spoken  language  that  the  child 
directs  his  first  efforts,  with  the  object  in  view  of  emitting  sounds  similar  to  those 
he  hears  ;  his  own  ear  instructs  him  concerning  the  success  of  his  attempts,  and 
at  every  moment  corrects  his  faults  of  articulation.  In  those  born  deaf,  the 
auditory  sensation  being  congenitally  absent,  articulate  speech  becomes  im- 
possible. This  is  a  fresh  example  of  the  close  link  which  connects  moveirient 
and  sensation  amongst  the  varied  forms  of  both. 


LANGUAGE  AND  IDEATION  655 

Thus  visual  images  in  the  deaf-mute  assume  a  preponderating  importance, 
further,  so  that  any  one  afflicted  in  this  manner  need  not  always  be  obliged  to 
-^^Tite  his  thoughts,  a  language  of  rajiid  manual  signs  whicli  replaces  articulated 
speech  has  been  invented. 

Functional  compensation,  tactile  images. — In  the  blind  visual  images  are  en- 
tirely wanting,  and  in  them  blindness  may  be  comiaensated  by  the  sense  of  touch, 
on  which  practice  will  confer  a  greater  acuteness.  The  blind  can  read  by  touch 
books  with  raised  lettering. 

The  case  of  Laura  Bridgeman  is  a  remarkable  one.  Becoming  blind  and  deaf 
at  the  age  of  two  years,  this  child  had  nothing  left  to  fall  back  upon  bvit  the  sense 
of  touch,  and  she  remained  uneducated  up  to  the  age  of  seven  years.  Doctor 
Howe,  by  the  aid  oi  signs  stamped  in  relief,  provided  for  her  a  tactile  speech  by 
which  she  covild  form  verbal  graphic  images,  and  could  thus  enter  into  intellectual 
relationship  with  those  surrounding  her.  Intelligence,  until  then  arrested  in  its 
development,  suddenly  took  possession  of  its  inlieritance. 

Part  played  by  the  muscular  sense. — The  sense  of  hearing  takes  part  in  sj)oken 
language,  the  sense  of  sight  in  written  language,  and  the  sense  of  touch  may 
artificially  svxpplement  either  or  both  of  these  senses.  It  must  be  observed  that 
the  muscular  sense,  which  is  another  variety  of  that  of  touch,  continuously  aids 
the  motor  phenomena  by  which  speech  and  writing  are  performed.  It  takes 
part,  it  is  true,  in  a  secondarj^  manner  ;  nevertheless,  its  activity  is  an  important 
•one.  Speech,  in  fact,  is  not  dependent  upon  the  ear  alone  in  order  to  yield  a 
suitable  articulation  of  sounds  ;  neither  is  writing  exclusively  dependent  upon 
sight  for  the  co-ordination  of  the  movements  of  the  hand.  If  absolutely  necessary, 
it  is  possible  to  write  with  the  eyes  closed ;  those  who  become  accidentally  deaf 
yet  preserve  the  power  of  articulation  and  the  intonations  of  speech.  Thus  the 
sensation  which  guides  and  regulates  the  muscular  movements  is  entirely 
mviscular  and  tactile. 

We  may  then,  even  in  individuals  in  possession  of  all  their  faculties,  admit 
the  existence  of  motor  images  (both  of  articulation  and  of  Avriting)  ;  only  those 
images  are  unconscious  ones.  In  deaf-mutes,  motor  representations  of  gestures 
acquire  an  exceptional  importance,  and  it  is  probable  that  they  perform  mental 
operations  by  means  of  these  representations,  just  as  we  oiu'selves  with  auditory 
or  visual  images. 

In  those  attacked  by  verbal  blindness,  who  have  thus  lost  the  faculty  of  read- 
ing, the  performance  with  the  right  hand  of  the  movements  necessary  for  copying 
a  word  will  sometimes  re-awaken  its  sjanbolical  signification. 

Remark. — Before  being  able  to  speak,  the  child  must  possess  some  auditory 
verbal  images  ;  and  before  being  able  to  wi'ite,  he  has  already  acquired  some 
A'isual  verbal  images.  Hjs  education  in  speaking  and  writing  has  the  effect  of 
creating  phonetic  and  graphic  motor  images  in  him.  The  latter  consist  in  asso- 
<'iations  of  eleiuents  called  centrifugal  or  motor,  as  do  the  former  in  those  of 
centripetal  or  sensory  elements.  We  may  here  point  out  that  neither  the  mutual 
association  of  centripetal  elements,  nor  that  of  centrifugal  eleinents  by  itself, 
alone  constitutes  systems  whose  function  is  isolated,  but  that  each  of  the  two, 
taken  individually,  is  initially  completed  by  the  adjunction  of  fibres  of  opposite 
■conductivity,  so  as  to  form  cyclic  systems  which  alone  are  capable  of  action. 
In  fact  impulses  reaching  the  auditory  nerve  are  quickly  refiected  to  the  motor 
nerves  of  the  adaptive  apparatus  of  the  ear,  and  those  which  reach  the  optic 
nerve  are  in  the  same  way  reflected  to  the  adaptive  apparatus  of  the  eye  ;  thus 
are  constituted  the  systems  which  we  call  sensorial,  merely,  however,  on  account 
■of  the  importance  taken  therein  by  the  phenomena  of  sensation  in  relation  to 
luoveinent,  but  which,  in  fact,  are  sensori-motor. 

Tlie  system  which  we  call  motor  (phonetic  or  graphic)  is  not  entirely  free  from 


656  SPECIAL  INNERVATIONS 

sensory  elements.  By  a  kind  of  converse  reflexion,  the  impulse  which  has 
descended  into  the  muscle  leaves  it  to  ascend  towards  the  brain  by  the  nerves 
of  the  muscular  sense.  Motor,  like  sensorial,  images  are  practically  aggregations 
in  which  either  motricity  or  sensibility  are  associated  in  unequal  proportions. 
By  their  mutual  association  in  the  exercise  of  the  function  of  spoken  or  written 
language,  these  sensorial  and  motor  systems  describe  an  arc  with  a  larger  ex- 
tension, indicating  the  general  course  of  the  impulse,  but  which  is  complicated 
by  a  certain  nvimber  of  partial  internal  cycles  which  must  be  taken  into  account 
in  the  analysis  of  tlie  general  mechanism. 

Voluntary  determination. — Thus,  by  association  of  sensations  in  time,  by  their 
diverse  forms  and  the  mutual  comparison  of  these  forms,  by  the  representations 
arising  from  this,  by  the  formation  of  images,  by  the  organization  of  the  latter, 
first  into  concrete,  later  into  abstract  ideas,  and  by  the  methodical  classification  of 
these  data  in  the  mind,  a  store  of  personal  experiences  is  laid  up,  which  goes  on 
increasing  in  proportion  to  the  number  of  new  sensations  added  to  the  preceding 
and  to  the  continuance  of  tlie  process  of  organization  to  which  they  are  sub- 
mitted. This  store  is  greater  than  we  ovrrselves  imagine.  Consciousness  only 
partially  illuminates  it,  and  usually  does  so  on  the  arrival  of  a  new  sensation 
evoking  the  series  of  psychical  acts  which  are  in  harmony  with  it.  Mechanisms 
habitually  unconscious  aid  in  abbreviating  these  operations.  Their  automatism 
suppresses  deliberation,  which  woxold  involve  delay.  Deliberation  has  no  in- 
fluence except  as  regards  the  function  of  direction,  which  is  alone  enlightened 
by  consciousness.  It  is  this  deliberation  which  causes  the  voluntary  act.  It  is 
this  which  determines  the  answer,  delays  or  precipitates  it,  and  dictates  its  mean- 
ing, according  to  motives  which  have  been  more  or  less  carefully  estimated  and 
compared. 

Automatic  language. — The  most  deliberate  premeditated  speech 
allows  in  its  performance  of  the  intervention  of  numerous  and  compli- 
cated automatisms.  It  may  even  become  entirely  automatic,  as  some- 
times happens  in  a  reading  or  recitation  delivered  without  regard  being 
paid  to  the  sense  of  the  words.  In  this  case  impulses  reach  the  muscles 
in  a  predetermined  order,  of  which  the  brain  alters  nothing,  resembling, 
in  a  sense,  the  more  or  less  complicated  electrical  waves  which,  in  a 
telephone,  proceed  from  the  manipulating  to  the  receptive  apparatus. 
The  reflex  arc  of  automatic  speech  may  connect  :  (1)  vision  with 
phonation  (automatic  reading)  ;  (2)  hearing  with  phonation  (echo  of 
speech)  ;  (3)  vision  with  writing  (copying)  ;  (4)  hearing  with  writing 
(dictation). 

In  these  examples,  language  becomes  reflex,  that  is  to  say,  uncon- 
scious, without  ceasing  to  be  cerebral.  Conversely,  it  may  remain 
conscious  and  have  no  external  motor  effect.  Language,  in  fact,  has^ 
the  very  closest  connexion  with  thought,  and  thought  is  a  continuous 
phenomenon.  Man  expresses  his  thought  in  speech,  but  he  first  thinks- 
that  which  his  speech  expresses. 

3.    Internal  language 

We  possess  an  internal  language  similar  to  external  language,  the 


LANGUAGE  AND   IDEATION  657 

only  difference  being  that  the  former  is  heard  by  ourselves  alone.  This 
language  is  spoken  only  in  the  sense  that  it  is  present  in  our  conscious- 
ness under  the  form  of  sonorous  images  of  which  the  rhythm,  tone, 
intonations  and  inflexions  are  habitual  to  us,  and  not  under  the  form 
of  the  visible  signs  of  writing,  or  other  analogous  symbols.  An  excep- 
tion must  be  made  in  the  case  of  deaf-mutes,  who  are  unacquainted 
with  the  audible  signs  of  language,  and  who  make  use  for  internal 
language  of  the  same  signs  as  those  employed  for  their  external 
language. 

Internal  speech  is  so  similar  to  external  speech  that  it  is  possible 
to  pass  insensibly  from  one  to  the  other  ;  a  loud,  low,  internal  voice 
and  u'hispering  are  merely  various  degrees  of  the  same  phenomenon. 
The  essential  difference  does  not,  indeed,  arise  from  the  relative  in- 
tensity of  the  vocal  motor  act,  but  from  the  fact  that,  in  internal  speech, 
we  have  no  other  auditor  or  interlocutor  but  ourselves.  Our  own 
speech,  whether  loud  or  low,  has  on  our  owti  hearing  and  on  that 
of  others,  the  effect  of  a  sensorial  excitation,  evoking  ideas,  suggesting 
answers,  and  so  on,  in  a  series  of  motor  sensitivo-motor  cycles  which 
engender  and  succeed  each  other  in  us  just  as  occurs  in  a  well-arranged 
train  of  thought  (Egger). 

The  relations  of  the  idea  to  the  word,  and  of  the  word  to  the  idea, 
are  the  same  both  in  internal  and  external  speech,  because  the  order 
and  succession  of  the  phenomena  are  precisely  similar  in  both.  In- 
ternal, like  external,  speech  is  autornatic  (as  is  often  the  case  in  mental 
prayer)  or  well  thought  out  (as  when  a  lecture  is  prepared). 

Internal  resonance. — How  is  it  possible  for  oui*  own  voice  to  resound  internally 
in  us  when,  apparently,  no  auditory  impulse  ascends  to  the  brain  ?  Whence 
•comes  the  impression  which  simulates  a  word  whispered  in  our  ear  wliich  has  no 
real  existence  ?  In  loud  speech  the  circulation  of  the  impulses  is  continuous  ; 
the  brain  stimulates  the  muscles  of  phonation,  which,  by  causing  the  air  to 
vibrate,  in  their  turn  stimulate  the  brain.  Thus  the  brain  retains  the  echo  of 
its  own  excitations,  which-  are  returned  to  it  in  the  order  in  which  it  sent  them 
itself  to  the  muscles  of  phonation.  In  internal  speech,  the  cycle  seems  to  be 
absolutely  broken  in  its  inferior  portion  and  is  really  so  between  the  larynx  and 
the  ear,  but  it  is  nevertheless  completed  by  other  paths.  The  air  no  longer 
vibrates,  but  the  muscles  are  not  absolutely  motionless. 

Motor  tendency. — In  internal  sjDeech,  self-observation  will  prove  the  occurrence 
of  very  slight  movements  of  the  tongue  and  lips,  and  this  to  some  extent  tends 
to  demonstrate  the  motor  quality  of  internal  language.  These  movements 
(incapable  of  causing  vibration  of  the  air)  have  a  sensory  echo  in  the  nervous 
system,  inasmuch  as  we  are  conscious  of  them.  The  cinsesthetic  sensations 
elicited  by  them  (muscular  sense)  give  rise  by  associations  to  corresponding 
auditory  sensations.  Internal  speech,  which  is  audible  only  to  ourselves,  would 
thus  be  an  instance  of  tactile  motor  images  which  are  perceived  as  auditory 
images.  Whatever  may  be  its  explanation,  the  fact  of  the  existence  in  internal 
speech  of  an  attenuated  motricity  is  imdeniable  :    every  sensory   impression  is 

P.  U  U 


658  SPECIAL  INNERVATIONS 

made  manifest  by  movement  or  tendency  to  movement.  Suspension,  adjonrn- 
ment,  arrest  of  the  motor  phenomenon  is  the  appanage  of  well  considered,  dehbe- 
rate,  and  voliintary  acts,  just  as  is  its  immediate  performance  that  of  reflex, 
unconscious  and  involxmtary  actions. 

Another  explanation. — The  circulation  of  the  impulses  in  internal  speech  may 
be  explained  in  yet  another  manner.  The  impulse  which  descends  from  the 
brain  to  the  grey  nuclei  of  the  inferior  system  for  the  performance  of  movements 
may  here,  perhaps,  undergo  a  reflexion  in  the  opposite  direction  which  may  cause 
it  to  re-ascend  to  the  brain,  thus  saving  itself  the  journey  which,  in  articulated 
speech,  it  would  be  forced  to  n:iake  from  the  motor  nuclei  to  the  muscles,  and 
thence  to  the  sensory  bulbo-medullary  nuclei  which  would  forward  it  once  again 
to  the  brain.  Instead  of  receiving  at  third  hand  an  impiolse  which  has  succes- 
sively passed  through  the  nuclei  and  motor  nerves,  through  the  muscles  and, 
finally,  through  the  nerves  of  muscular  sensibility,  the  sensory  bulbar  nuclei 
receive,  directly  from  the  brain,  an  impulse  having  the  form  of  the  movement 
which  it  is  intended  to  accomj)lish,  and  they  send  it  once  more  to  the  brain 
to  announce  the  no -longer  muscular,  but  entirely  nervous  performance  of  the 
act  controlled  by  it.  In  this  intra-nervous  circulation,  the  brain  speaks  to  itself 
without  indiscreet  witness  ;  it  understands  and  perceives  its  own  commands, 
without  their  being  revealed  to  the  external  world,  except  by  imperceptible 
muscular  oscillations,  of  an  intensity  which  varies  greatly,  according  to  the  in- 
dividual. This  internal  cycle  probably  duplicates  the  external  cycle,  not  ixierely 
in  internal  and  low,  but  also  in  loud  speech,  and  takes  part  in  what  are  called 
cinsesthetic  impressions.  It  is  thus  at  least  that  this  sense  of  motor  innervation, 
which  some  have  maintained  to  be  on  an  equality  with  the  muscular  sense,  may 
be  understood,  and  this  without  infringing  the  most  fundamental  laws  of  the 
nervous  system,  namely,  that  of  the  propagation  of  the  imjxilses  in  a  definite 
direction,  and  that  of  the  difjtinction  of  the  two  opposite  currents  ensuring  this 
propagation. 

We  can  imagine  all  communication  interrupted  between  the  organs  of  the 
senses  and  their  nuclei  of  origin,  and  at  the  same  time  between  the  motor  nuclei 
and  the  muscles  ;  still,  internal  si^eech  would  not  on  this  accoimt  be  supx^ressed, 
any  more  than  thought,  which  it  interprets  to  us  under  a  conscious  form. 

1.  Intelligence  and  consciousness. — Consciousness  and  intelligence 
are  closely  connected,  and  we  see  that  those  beings  who  are  the  most 
self-conscious  are  generally  at  the  same  time  the  most  intelligent  ; 
but  consciousness  and  intelligence  are,  nevertheless,  distinct  from 
each  other.  Consciousness  involves  an  idea  of  actuality  :  it  is  this 
which  enlightens  the  internal  operations  of  the  mind  ;  it  ceases  to  be  an 
actuality  when  these  operations  are  withdrawn  from  this  internal 
enlightenment.  No  explanation  can  be  given  of  so  elementary  a 
phenomenon  ;  it  embraces  itself  in  its  entirety,  containing  and  con- 
tained. 

Intelligence  involves  an  idea  of  cajjacity  :  it  may  be  estimated  by  the 
number,  the  complexity  and  the  organization  of  the  internal  repre- 
sentations, images,  and  ideas  that  the  mind  in  the  course  of  its  in- 
numerable experiences  is  susceptible  of  acquiring.  It  is  developed  in 
the  consciousness,  but  survives  it  as  long  as  the  organization  of  the 
representations   subsists   in  its  first   perfection.     The   mathematician 


LANGUAGE    AND    IDEATIOX  659 

who  seeks  the  solution  of  a  problem  has  only  the  principal  relationship 
between  the  values  present  in  his  consciousness. 

2.  Attention. — Phenomena  conveying  the  sense  of  spontaneity  are, 
of  all  others,  the  most  difficult  to  explain.  In  fact,  they  seem  to  be  in 
conflict  with  the  ordinary  laws  of  causation,  such  as  they  appear  to  us 
in  the  physical  world,  and  such  as  we  wish  to  extend  them  to  all  phe- 
nomena whatsoever  with  the  aim  of  unification.  Attention,  will,  all 
the  acts  in  which  psychical  effort  takes  part,  are  of  this  nature.  It  is 
true  that  in  a  large  number  of  cases  this  idea  of  spontaneity  is  partly 
dissipated  by  analysis,  as  being  a  delusion.  The  sense  of  tension  which 
we  experience  is  really  a  psychical  phenomenon,  but  it  is  a  secondary 
one  ;  it  is  a  sensation  which  arises,  at  least  in  part,  from  the  involuntary 
tonic  contraction  of  our  muscles.  If  the  attention  seems  of  itself  to  be 
directed  to  an  external  object  or  an  internal  representation,  it  may  also 
be  aroused  by  an  external  or  internal  excitation  in  the  same  direction. 

Attention  increases  the  degree  of  consciousness  ;  it  carries  it  in  a 
given  direction,  which  grasps  it,  or,  as  is  often  said,  concentrates  it ; 
that  is  to  say,  exalts  it  as  regards  a  certain  sense  (sight,  hearing,  etc.), 
and  diminishes  it  to  the  same  extent  as  concerns  others.  The  period 
of  its  perception  is  a  very  short  one.  For  example,  with  regard  to  a 
sound  first  lieard,  this  period  has  a  given  duration  ;  for  a  second  sound 
which  the  ear  anticipates,  it  may  be  diminished  by  half  and,  the  stimulus 
being  the  same,  the  sensation  is  equally  intensified.  At  the  same  time, 
the  residues  of  anterior  sensations  are  recalled  and  swell  the  flood  of 
new  impulses  circulating  in  the  nervous  system.  While  it  lasts,  atten- 
tion suppresses  the  motor  acts,  and  inhibits  the  muscular  organs. 
This  suspension  of  motor  impulses  favours  the  deliberation  which 
takes  place  in  the  mind.  The  unkno\^ai  once  placed  aside,  the  im- 
pulses which  the  attention  has  heaped  up  by  momentarily  suspending 
them,  are  launched  on  a  career  towards  a  distinctly  determined  end, 
and  the  motor  acts  prepared  by  the  tension  are  executed. 

At  the  same  time  that  these  changes  take  place  in  ourselves,  in  what  we  call 
the  activity  of  the  mind,  others,  more  or  less  visible,  are  the  consequence  of  it 
as  regards  the  exercise  of  our  functions  both  internal  and  external.  We  have 
just  pointed  out  that  the  muscular  tissue  and  the  motor  apparatus  take  an  obvious 
part  in  the  function  of  attention.  Not  only  is  its  attitude  a  special  one,  but  also 
its  aptitudes  are  modified.  Like  physical  labour,  intellectual  labour  if  prolonged 
brings  about  fatigue.  Although  not  precisely  similar  in  both  cases,  the  analogies 
and  the  resemblances  are  great.  This  results  from  the  fact  of  intellectual  and 
'physical  labour  never  being  entirely  independent  of  each  other.  Sonaetimes  one 
and  sometimes  the  other  predominates  more  or  less,  according  to  circumstances. 

3.  Fatigue. — The  different  conditions  of  the  production  of  fatigue 
have  been  carefully  studied  by  Mosso. 

UU* 


660  SPECIAL  INNERVATIONS 

If,  by  repeated  and  equal  excitations,  we  compel  a  muscle  to  yield  the  same 
contraction,  and  the  amount  of  this  contraction  be  registered  each  time,  after  a 
certain  period,  its  loss  of  power,  and  finally  its  total  exhaustion,  will  be  rendered 
evident  by  the  lessened  elevation  of  the  tracings  on  the  paper.  The  line  which 
joins  the  superior  extremities  of  these  tracings  is  the  curve  of  fatigue  (Kronecker). 
It  is  the  more  marked  in  proportion  as  the  fatigue  is  the  more  quickly  produced. 
It  may  then  be  considered  as  an  evidence  and  an  estimation  of  the  fatigue  itself. 
The  experiment  is  carried  out  on  a  finger,  the  movements  of  flexion  of  which 
are  made  use  of  to  raise  a  given  weight.  Tlie  myographic  apparatus  adapted 
to  this  test  is  an  ergograph  (a  register  of  work  done)  ;  this  kind  of  myography 
adapted  to  the  special  stvidy  of  fatigue  and  the  divex'se  conditions  of  its  production 
is  ergographia. 

Each  rise,  each  double  tracing  inscribed  by  the  elevation  and  the  descent  of 
the  lifted  weight,  is  a  test  of  force  capable  of  estimating  the  maximum  labour. 
The  whole,  that  is  to  say,  the  curve  of  fatigvie,  is  a  test  of  endurance,  and  is  the 
most  interesting. 

We  have  an  instrument  with  which  we  can  estimate  fatigue  ;  we  see  the  latter 
produced  as  the  result  of  repeated  efforts.  Where  is  it  situated  ?  In  the  muscle 
itself  or  in  the  nervous  system  ?  And  as  this  latter  is  complex,  in  which  of  its 
segments  and  superposed  systems  ?  The  problem  is  a  complicated  one.  Fatigue 
is  both  an  objective  and  a  subjective  phenomenon.    ' 

Objectively,  fatigue  is  ultimately  a  destruction  (not  sufficiently  com- 
pensated by  the  converse  current  of  reparation,  which  is  never  wanting). 
Direct  analysis  attests  that  it  is  especially  in  the  muscle  that  this 
destruction  goes  forward,  as  the  muscle  is  the  great  spendthrift  -of 
physical  energy  accumulated  in  the  organism. 

Subjectively^  fatigue  is  a  painful  sensation,  of  which  the  approximate 
condition  lies  in  the  impression  aroused  by  the  destruction  of  the 
fatigued  organs,  in  the  sensory  nerves  with  which  they  are  provided. 
From  this  point  of  view  it  is  nervous  and  cerebral.  The  nervous  system 
takes  part  in  the  concatenation  of  the  phenomena  in  order  to  arrest 
the  cause  of  the  movement,  by  suppressing  the  impulse  which  it  trans- 
mits to  the  muscular  system,  and  so  stopping  the  destruction  which 
would  be  the  consequence  of  it. 

Fatigue  may  be  differently  felt  by  different  individuals,  according 
to  their  peculiar  sensibility.  One  will  complain  of  a  marked  fatigue 
when  the  destruction  has  hardly  commenced,  another  does  not  feel 
any  fatigue  when  the  destruction  is  far  advanced  ;  and  when  these 
differences  are  very  marked,  they  are  both  prejudicial,  as  they  denote 
and  occasion  a  want  of  equilibrium  in  the  functions.  Sensation  does 
not  play  its  part,  which  is  not  only  to  excite,  but  also  to  weigh,  regu- 
late, and  economize  movement.  Thus  it  is  in  the  healthiest  subjects 
that  the  sensation  of  fatigue,  or,  in  one  word,  fatigue,  best  exerts  its 
moderating  action  by  arresting  muscular  effort. 

Secondary  effects  of  intellectual  activity. — Thus  physical  work  induces  a  psychi- 
cal condition  which  keeps  it  within  boimds  by  the  operation  of  one  of  the  funda- 


LANGUAGE   AND   IDEATION  661 

mental  reactions  of  the  nervous  system.  Intellectual  labour,  in  its  turn,  is  the 
cavise  of  a  physical  waste,  much  less,  it  is  true,  but  still  appreciable.  The  absence 
of  movement  of  the  luuscles  during  the  exercise  of  attention  does  not  always 
imply  their  inactivity,  but  often  conceals  a  certain  tension.  In  this  respect 
there  are  gi*eat  differences,  according  to  the  individual  and  also  to  the  degree  of 
effort  which  accompanies  the  exercise  of  the  attention.  In  some  a  relaxation 
of  the  fingers  may  be  observed  (INIacDougal).  In  every  case  intellectual  activity 
modifies  the  aptitude  of  the  nervous  sj^stem  to  give  rise  to  muscular  contractions. 
This  is  made  manifest  by  the  trgograpliic  test  when  applied  at  the  end  of  difficult 
and  prolonged  psychical  labour.  The  curve  of  fatigue  appears  with  much  greater 
rapidity.  Just  as  excess  of  physical  labour  temporarily  diminishes  intellectual 
activity  or  aptitude,  so  does  excess  of  intellectual  laboiu*  diminish  physical 
activitj'  or  aptitude.  We  say  excess,  for  if  fatigue  be  avoided  the  contrary 
resvilts  :  a  small  amount  of  work  increases  the  muscular  force,  and  this  augmenta- 
tion is  evidenced  by  the  test  of  endurance  and  also  by  that  of  force. 

The  reaction  of  psychical  effort  carried  so  far  as  to  induce  fatigue  does  not 
confine  its  effect  to  the  external  motor  apparatus  ;  the  systein  of  organic  life 
also  feels  this  reaction.  During  the  exercise  of  attention,  the  pupil  dilates 
(Mentz),  the  convergence  of  the  two  eyes  diminishes,  and  the  crystalline  lens 
becomes  flattened  (Heini'ich)  ;  the  body  temperatm'e  may  also  be  increased 
(Gley). 

The  circulation  and  the  respiration  undergo  modifications.  A  short  and 
energetic  intellectual  effort  produces  cardiac  and  respiratory  acceleration,  and  a 
vaso-motor  constriction  of  the  peripheral  vessels,  followed  by  a  slight  slackening 
of  these  movements. 

An  intellectual  task  lasting  several  hom's,  the  body  being  in  repose,  causes 
weakening  of  the  heart's  action,  and  a  contraction  of  the  peripheral  capillary 
circulation.  This  contrast  is  also  observed  in  muscular  exercise,  only  the  figures 
are  changed  in  value. 

Effects  on  the  cerebral  circulation. — But  the  most  interesting  changes  in  the 
cii'culatory  systems  are  those  affecting  the  brain.  If  the  cerebral  and  the  radial 
pulse  are  simviltaneously  compared  (in  a  case  of  loss  of  a  portion  of  the  skull),  it 
will  be  found  that,  diu-ing  intellectual  activity,  only  the  amplitude  of  the  former 
is  augmented  (Mosso).  The  same  thing  has  been  observed  by  comparison  of 
the  radial  and  the  carotid  arteries  (Gley).  The  brain  increases  in  voluine  from 
the  fact  of  its  augmented  cu"culation.  Hyperaemia  of  the  brain  is  not  only  a 
consequence,  but  also  an  effect  of  cerebral  activity  (Morselli).  Like  other  organs, 
the  circulation  in  the  brain  is  adapted  to  the  functions  of  the  latter,  and  is  regu- 
lated by  them.  The  brain,  thovigh  a  nervous  organ,  which  is  both  a  receiver  and 
disjoenser  of  impulses,  s>i  which  it  maintains  an  inexhaustible  reserve,  is  none 
the  less  subject  to  the  same  law  as  other  organs.  It  is  through  the  spinal  cord 
and  the  great  sympathetic  that  it  sends  to  itself  (to  its  vessels)  the  vaso-motor 
impulses  which  govern  its  circulation  (recurrent  motricity)  ;  it  is  by  the  medulla 
oblongata  and  the  trigeminal  nerve  that  it  convej^s  in  a  contrary  direction  the 
sensory  impulses  which  take  part  in  this  controlling  cycle  (recui-rent  sensibility). 

B.     LANGUAGE  AND  CEREBRAL  LOCALIZATIONS 

The  mental  mechanism  of  which,  by  the  enhghtenment  of  our  con- 
sciousness we  have  an  internal  perception,  is  presided  over  by  a  physical 
mechanism  which,  in  the  brain  of  a  being  distinct  from  ourselves,  would 
appear  to  us  as  being  matter  in  movement,  if  we  were  possessed  of 
physiological  methods  sufficiently  perfect  to  unveil  to  us  the  delicate 

u  u** 


662  SPECIAL  INNERVATIONS 

and  innumerable  modifications  which  take  place  in  the  course  of  all 
these  actions.  But  we  are  far  indeed  from  the  attainment  of  such  a 
result.  Nevertheless,  a  start  has  been  made  as  regards  the  performance 
of  this  analysis,  in  so  far  as  portions  of  the  brain  which  preside  over 
certain  functions  or  operations  of  the  mind  are  differentiated. 

We  already  know  that  each  specific  sensation  (each  particular  form  of  sensa- 
tion) is  located  in  a  special  system  which,  were  it  entirely  abolished,  would  cause 
all  trace  of  the  corresponding  sensations  to  disappear,  and  at  the  same  time 
would  prevent  all  possibility  of  their  renewal.  We  also  know  that  mutilation 
effected  at  the  periphery  of  such  a  system,  by  separating  it  from  its  normal 
stimulus,  renders  impossible  that  formation  of  physical  images  which  is  essential 
for  the  renewal  of  the  sensation,  but  allows  of  the  subsistence  of  the  psychical 
images  stored  up  in  the  memory.  We  also  know  that,  conversely,  the  removal 
of  determinate  regions  of  the  cortex,  which  are  the  culminating  points  of  each 
of  these  systems — while  permitting  the  renewal  of  the  stimulus  at  the  periphery, 
and  also  the  persistence  of  certain  reflex  automatic  or  instinctive  manifestations, 
of  unconscious  or  subconscious  nature,  which  are  united  to  the  organization  of 
the  sub-cortical  portion  of  the  system — destroys  the  provision  of  corresponding 
psychical  images. 

Pathological  dissociation  of  the  elements  of  language.- — But  the  visual,  like  the 
auditory,  images  are  more  or  less  complicated  representations.  Below  the  images 
properly  so  called,  exist  sensations,  which  are  their  elements.  The  images  result- 
ing from  their  grouping  are,  some,  concrete  (images  of  objects),  others,  symbolical 
or  abstract  (verbal  images,  or  those  of  language  whether  spoken  or  wTitten). 
Pathology  demonstrates  that  some  of  these  images  may  disappear,  while  others 
are  preserved  more  or  less  unaltered.  The  disappearance  thus  effected  may 
concern  the  sensations  or  images  of  a  given  sense,  while  allowing  of  the  sub- 
sistence of  those  of  other  senses  ;  a  choice  may  also  be  made  between  the  more 
or  less  complicated  orders  of  the  different  images  or  representations  of  this  sense. 
It  may,  for  example,  suppress  the  verbal  images  of  hearing  or  of  vision,  while 
allowing  the  images  of  objects  to  persist,  and  natm-ally  also  the  sensations,  in  a 
more  or  less  partial  manner.  It  may  suppress  all  the  psychical  images  and  only 
permit  the  sensations  to  remain  ;  and,  finally,  it  may  destroy  the  psychical 
manifestations  of  a  sense  so  utterly  that  nothing  of  it  remains. 

Aphasia. — When  the  distiu-bance  of  which  the  brain  is  the  seat  is  limited  to 
the  suppression  of  verbal  images,  aphasia  ensues.  The  person  suffering  from 
aphasia  is  not  also  the  victim  of  aphonia,  for  he  preserves  intact  the  motor  powers 
of  language,  though  he  is  incapable  of  using  them.  Neither  is  he  to  be  considered 
as  mentally  affected,  for  he  possesses  ideas  wdiich  he  is  incapable  of  expressing. 
A  disturbance  of  this  nature,  which  respects  both  the  inferior  sensori-motor 
activities  and  also  to  a  certain  extent  the  formation  of  ideas,  is  necessarily  a 
local  disturbance.  It  is  indeed  seated  in  the  brain  and,  further,  it  only  affects 
in  this  organ  one  of  the  systems  participating  in  the  function  of  language  ;  for, 
were  it  to  involve  all  these  systems  simultaneously,  it  would  not  be  the  expression 
of  the  idea  alone,  which  would  disappear,  but  also  the  idea  itself.  As  ideation 
has  many  soiu-ces  (audition,  vision  .  .  .)  and  equally  numerous  means  of  expres- 
sion (speech,  writing  .  .  .),  it  persists,  but  in,  it  is  true,  a  more  or  less  shattered 
condition.  A  person  suffering  from  aphasia  is  an  individual  who  has  not  lost  the 
whole  function  of  language,  but  one  of  the  factors  taking  part  in  this  complex 
function. 

The  lesion  giving  rise  to  aphasia  presents  distinct  anatomical  and  functional 
forms.     Sometimes  it  destroys,  in  the  cortex  itself,  the  partial  systems   which 


LANGUAGE   AND    IDEATION  663 

give  rise  to  verbal  images  {cortical  aphasias).  Sometimes  it  interrupts  the  com- 
mvmications  of  these  systems  with  each  other,  or  with  the  inferior  systems  for  the 
reception  of  sensation,  or  for  the  performance  of  movements  {aphasias  of  conduc- 
tion). But,  even  in  the  brain,  we  distinguish  between  systems  for  the  reception 
and  organization  of  sensations  and  those  for  the  performance  of  motor  verbal 
function  ;  whence,  according  to  the  seat  of  the  lesion  in  one  or  other  system, 
we  find  two  functionally  different  forms  of  apliasia,  one  sensorial  and  the  other 
motor. 

1.     Aphasias  known  as  cortical 

Some  verbal  images  are  sensorial  and  others  motor.  The  first  are 
more  or  less  complex  representations,  which  are  awakened  in  us  in  a 
passive  manner  at  the  instigation  of  the  signs  (audible  or  visible)  of 
language.  They  fully  merit  the  name  of  images,  because  they  are 
spread  out  in  the  open  light  of  consciousness,  and  lend  themselves  to 
internal  analysis.  The  second  resemble  them  inasmuch  as  they  also 
are  associations,  ready  prepared  and  easily  to  be  evoked  ;  but  they 
differ  from  them  in  that  their  cerebral  mechanism  eludes  a  subjective 
analysis,  and  that  the  representations  caused  by  them  are  secondary, 
that  is  to  say,  posterior  to  the  physical  or  muscular  act  which  they 
determine  or  solicit.     They  are  only  images  in  a  metaphorical  sense. 

Further,  the  sensorial  images  are  not  entirely  free  from  motor  effect, 
if  only  those  movements  of  adaptation  are  taken  into  account  which 
are  necessarj^  to  the  functional  activity  of  every  organ  of  the  senses  at 
the  moment  when  the  stimulation  falls  on  it ;  any  more  than  the  motor 
images  are  quite  free  from  sensory  effect,  on  account  of  the  impulse 
which,  from  the  muscles,  ascends  to  the  brain  to  register  the  accom- 
plished movement. 

Language,  which  is  a  complex  function,  associates  sensori-motor 
cycles  into  a  cycle  of  aggregation.  In  this  association  some  of  these 
partial  cycles  assume  essentially  a  sensorial  function  (auditory  or  visual 
system),  and  others  essentially  a  motor  function  (tactile  systems).  As 
these  systems  are  localized  in  distinct  regions  of  the  brain,  it  follows 
that,  according  to  the  system  involved,  the  aphasia  will  be  either 
sensorial  or  motor. 

A.  Motor  aphasli. — In  the  gradual  development  of  the  question, 
the  aphasia  styled  motor  was  the  first  to  be  observed  ;  and  it  is  con- 
nected, as  is  well  kno^\Ti,  with  the  problem  of  the  functional  localiza- 
tions of  the  brain.  Broca  has  proved  that  loss  of  articulate  speech  is 
the  result  of  the  destruction  of  the  third  frontal  convolution  of  the  left 
hemisphere.  The  individual  thus  attacked  preserves  his  intelligence. 
If  the  lesion  does  not  transgress  the  limits  just  indicated,  he  may  be 
immune  from  all  motor  paralysis  ;  the  emission  of  sounds  is  possible  ; 
the  apparatus  of  phonation,  properly  so  caUed,  is  intact ;  but  although 


664  SPECIAL  INNERVATIONS 

the  patient  is  conscious  that  he  might  turn  it  to  account  for  the  com- 
munication of  his  ideas,  it  is  impossible  for  him  to  make  use  of  it.  He 
retains  the  faculty  of  internal  language,  but  external  language  is 
impossible. 

This  incapacity  is  explained  by  saying  that  he  has  lost  the  motor 
memory  of  the  articulation  of  words.  His  store  of  motor  images  of 
articulation  is  destroyed  from  the  fact  of  the  destruction  of  the  third 
left  frontal  convolution. 

Agraphia.— It  may  sometimes  happen  that,  while  speech  is  preserved, 
writing  is  impossible  :  this  is  called  agraphia.  An  attempt  has  been 
made  to  localize  the  lesion  of  this  disturbance  of  language  in  the  foot 
of  the  second  frontal  convolution  (Exner)  ;  but  this  localization  has 
been  disputed. 

B.  Sensorial  aphasia. — Wernicke  subsequently  distinguished  a 
new^  form  of  aphasia,  called  by  him  "  sensorial,"  which  differs  from 
the  preceding  by  its  symptoms  and  the  seat  of  the  lesion.  The  person 
affected  by  this  form  of  aphasia  can  articulate  sounds  or  write,  and 
may  even  be  verbose  ;  but  the  disorder  of  language  is  shown  by  the 
fact  that  his  words  have  no  meaning,  or  do  not  answer  to  the  question 
put  to  him.  Sometimes  he  has  lost  his  verbal  auditory  images  (word 
deafness),  and  it  is  in  this  case  that  sensorial  aphasia  is  most  markedly 
evident ;  sometimes  he  has  lost  his  verbal  visual  images  (word  blind- 
ness), and  the  disturbance  of  the  function  of  language  is  rendered 
manifest  by  his  inability  to  read.  The  written  signs  have,  for  him,  lost 
their  symbolical  signification  ;  he  can  write,  but  cannot  read  what  he 
has  written  ;  he  can  speak  and  answer  an  oral  question,  but  not  a 
written  one. 

Word  deafness. — Word  deafness  is  observed  in  the  case  of  injury  to 
the  first  temporal  convolution  on  the  left  side.  The  area  of  the  cortex 
which  originates  verbal  auditory  images  thus  includes  almost  the  whole 
of  the  terriotry  of  audition  ;  a  limited  lesion  of  the  left  side  allows  of 
the  persistence  of  the  sonorous  sensations  or  of  pitch,  while  destroying 
its  symbolical  significance. 

Word  blindness. — Word  blindness  is  observed  as  the  result  of  destruc- 
tion of  the  left  inferior  parietal  lobule  with  or  without  participation  of 
the  angular  gijrus.  It  therefore  usually  accompanies  agraphia.  Pure 
word  blindness,  without  being  complicated  with  agraphia,  has  been 
observed  in  the  case  of  interruption  of  the  inferior  longitudinal  tract 
of  Burdach  (inferior  portion  of  this  tract). 

It  seems,  therefore,  as  if  the  fibres  of  the  longitudinal  tract  were 
employed  to  put  the  cortical  area  of  vision  into  communication  with 
the  area  of  language  (Dejerine).     The  homonymous  hemianopsia  which 


LANGUAGE   AND    IDEATION  665 

accompanies  this  lesion  is  due  to  the  concomitant  atrophy  of  the  optic 
radiations. 

Verbal  auditory  amnesia. — Word  deafness  is  a  permanent  lesion,  at 
least  in  the  conditions  under  which  it  is  usually  observed  ;  but  it  some- 
times displays  itself  in  a  transitory  and  attenuated  form,  either  under 
toxic  influences,  such  as  that  of  tobacco  (G.  Ballet),  or  by  the  progress 
of  old  age.  For  if  our  store  of  internal  experiences  always  goes  on 
increasing,  we  have  more  and  more  trouble  in  making  use  of  it,  evoca- 
tion of  words  being  performed  with  difficulty  and  sometimes  uselessly. 
And  it  is  under  these  circumstances  that  their  disappearance  follows 
a  fairly  regular  order,  proper  names  being  the  first  to  go,  then  common 
nouns,  while  adjectives  and  verbs  are  remembered. 

Visual  verbal  amnesia. — This  is  less  well  known  than  the  preceding, 
and  always  difficult  to  differentiate  from  other  disturbances  of  the 
same  nature,  and,  very  exceptionally,  it  occurs  in  a  transitory  form. 

Sensorial  types. — Hearing  is  the  sense  usually  employed  for  the 
registration  of  verbal  images,  on  account  of  the  infinitely  greater  use 
we  make  of  speech  than  of  writing.  Sight,  on  the  contrary,  is  the 
sense  which  registers  the  images  of  objects,  because  vision  has  in  this 
respect  a  permanence  of  action  and  a  precision  which  hearing  does 
not  possess.  But  there  are  individuals  in  whom  internal  speech_,  or 
the  operations  of  the  mind,  more  resemble  reading  than  internal  audi- 
tion ;  these  persons  are  called  visuals,  in  opposition  to  aiiditives,  in 
whom  auditory  images  have-  an  almost  exclusive  preponderance  and 
use.  Further,  motors  are  distinguished,  in  whom  internal  speech 
would  be  the  representation  of  a  movement  of  articulation,  and  the 
indifferent,  in  whom  these  various  images  would  be  employed  according 
to  circumstances.  These  distinctions,  established  by  Charcot,  and  to 
which  exception  has  sometimes  been  taken,  are  considered  as  funda- 
mental by  a  fairly  large  number  of  neurologists. 

Amusia. — Music  also  is  a  language,  but  one  that  is  expressive  of 
emotions,  and  not  representative  of  ideas.  In  any  case  it  has  its 
symbols,  which  form  in  the  musician  a  store  of  musical  images.  It  is 
possible  for  these  images  to  be  lost  in  the  same  way  as  verbal  images. 

Amimia. — Mimicry  is  a  language  more  primitive  and  more  general 
than  language  properly  so  called  ;  it  is  possible  for  the  images  of 
mimicry  to  be  lost.     Brissaud  describes  an  aphasia  of  intoriation. 

2.     Aphasias  from  default  of  conduction 

Aphasia,  in  its  different  forms,  is  brought  about  by  lesions  of  the 
cortex,  the  seat  of  which  we  have  just  pointed  out.  To  each  of  these 
regions  is  attributed  a  power  of  preservation  of  those  images,  either 


666  SPECIAL  INNERVATIONS 

sensorial  or  motor,  which  take  part  in  the  function  of  language.  It  is 
even  generally  maintained  that  these  images  are  included  therein. 
This  manner  of  propounding  the  localization  of  language  and  its  prin- 
cipal mechanisms  goes  beyond  the  ascertained  facts.  These  latter 
incontestably  prove  that  each  of  these  regions  is  an  essential  portion 
of  the  nervous  mechanism  of  language.  But  this  mechanism  is  capable 
of  being  changed  and  arrested  as  regards  its  function  by  lesions  other 
than  those  of  the  cortex.  For  aphasia  to  be  produced,  it  is  necessary 
and  sufficient  that  the  principal  associations  presiding  over  the  function 
of  language  be  interrupted.  In  some  points  this  rupture  is  brought 
about  by  the  destruction  of  certain  regions  of  the  cortex  ;  but  it  may 
also  be  induced  by  interruption  of  the  white  tracts,  whose  dejBnite 
function  it  is  to  mutually  associate  these  regions,  or  by  that  of  the 
fibres  of  projection  terminating  in  them  or  immediately  leaving  them. 
These  are  called  the  aphasias  of  conductivity. 

Essential  difference. — The  symptomatological  difference  lies  in  the 
important  fact,  that  internal  language,  corresponding  to  the  loss  of  the 
images  whence  aphasia  results,  is  then  preserved.  There  is  no  oblitera- 
tion of  an  order  or  a  form  of  images,  but  rupture  of  the  connexions 
which  must  normally  exist  between  these  images  for  speech  or  for 
writing  to  be  properly  carried  out.  To  put  it  otherwise,  the  internal 
organization  of  the  partial  systems  which  ensure  the  formation  of  motor 
or  sensorial  images  (organization  carried  out  by  the  above-mentioned 
regions  of  the  grey  matter)  is  not  compromised,  but  there  is  a  separation 
of  these  different  systems,  together  with  the  impossibility  of  uniting  in 
common  functions  for  the  future  (associations  effected  by  certain  fibres 
extending  in  a  large  number  from  one  to  the  other  of  these  regions 
through  the  white  matter).  Injuries  affecting  the  region  of  the  insula, 
situated  immediately  between  the  regions  called  sensorial  and  those 
called  motor,  produce  aphasia  of  this  nature  by  section  of  the  white 
tracts  of  association  passing  through  it  (Dejerine). 

Schematic  constructions. — Charcot,  Lichteim,  Grasset,  and  several  other 
authors  have  constructed  schemes  intended  to  facihtate  tlie  comprehension  of 
the  mechanisni  of  language,  as  well  as  its  disturbance  in  different  aphasias.  That 
of  Grasset,  inasmuch  as  it  aims  less  at  the  clinical  reality  of  the  different  disturb- 
ances observed,  is  the  one  most  appropriate  for  the  concrete  representation  of 
the  different  questions  discussed  with  regard  to  the  analysis  of  language  in  its 
normal  or  disturbed  condition.  By  connecting  together  the  four  cortical  centres 
(two  for  sensation,  two  for  motion)  which  preside  over  this  function,  a  sort  of 
horizontal  polygon  is  prodiiced,  of  which  these  areas  of  the  cortex  form  the  angles. 
From  these  same  angles  start  ascending  vertical  lines,  to  represent  the  sensorial 
nerves,  and  descending  lines  for  the  motor  nerves.  By  the  associations  here 
produced  between  sensation  and  movement,  this  polygon  ensures  both  the  physio- 
logical and  psychological  automatism  of  the  functions  of  language.       But  these 


LANGUAGE    AND    IDEATION 


667 


functions  are  not  entirely  automatic  :  they  are  sometimes  intellectual.  Hence 
each  of  these  centres  is  once  again  joined  by  lines  to  a  superior  centre,  to  that  of 
intelligence. 

Without  speaking  of  the  destruction  of  the  centres  themselves,  the  interruption 
of  the  conductors  may  be  either  intra-polygonal  (separation  of  the  centres  in 
automatic  function),  sub-polygonal  (separation  of  the  centres  from  their  peri- 
pheral connexions),  or  supra-polygonal  (separation  of  the  polygonal  centres  from 
the  superior  centre  of  ideation),  and  the  symptoms  vary  accordinglj^  Anatomi- 
call5%  all  these  centres  are  situated  in  the  cortex, while  all  the  white  fibres  connect- 
ing them  (both  mutually  with  the  inferior  regions,  and  with  the  centre  of  ideation) 
are  located  below  the  cortex.     By  giving  to  the  expressions  a  symbolical  mean- 


Cortical  Aphasias. 
0 


Supra-cortical  Aphasias.  Trans-cortical  Aphasias. 

Fig.  261. — Diagrams  representing  the  different  classes  of    aphasias  and  the  different 
forms  which  they  may  individually  assimie. 

I,  II,  III,  IV,  four  classes  of  aphasias,  according  to  the  seat  of  the  lesion,  whether  in  the  grey 
matter  (special  centres),  in  the  white  matter  (in  the  course  of  the  fibres  of  projection  of  these 
centres),  in  the  white  matter  (in  their  tracts  of  mutual  association),  in  the  white  matter  (in  their 
tract  of  communication  with  the  superior  centre  of  ideation). 

A,  auditory  centre  ;  "V,  visual  centre  ;  M,  motor  centre  of  articulation  ;  E,  motor  centre  for 
writing  ;    O,  intellectual  centre  (after  Grasset). 


ing  which  elucidates  their  function,  G-rasset  calls  the  intra-polj'gonal  fibres 
trans-cortical,  the  sub-polygonal  sub-cortical,  and  the  supra-polygonal  supra- 
cortical,  all  of  them  converging  towards  the  centre  O,  or  superior  centre  of 
ideation. 

Principal  differences — 1.  Cortical  aphasias  and  those  of  conduction. — Between 
cortical  aphasias  and  aphasias  the  result  of  lack  of  conduction,  the  difference  is 
that,  for  example,  in  the  first,  one  of  the  systems  presiding  over  the  formation 
and  conservation  of  verbal  images  (aviditory,visual,  motor)  is  destroyed  as  regards 


668  SPECIAL    INNERVATIONS 

its  essential  portion  (corresponding  cortical  centre)  ;  while  in  the  second  these 
systems  jDersist.  In  the  first  case  the  images  disajopear  ;  in  the  second  they  are 
preserved,  and  only  lack  the  power  of  forming  certain  connexions  between  them- 
selves and  with  the  external  world.  Thus  cortical  aphasias  are  more  serious  than 
the  aphasias  of  conduction,  since,  in  them,  the  group  of  images  is  no  longer  con- 
nected in  a  definite  manner,  but,  further,  its  function  has  disappeared. 

2.  Sub-cortical  aphasias. — In  sub-cortical  aphasias  internal  language  seems  to 
he  almost  intact.  All  images  persist  ;  but  if  the  sub-cortical  lesion  is  in  one  of 
the  two  sensory  fields,  they  are  not  renewed  in  the  corresponding  area  ;  if  it  is 
in  the  motor  field,  they  are  no  longer  expressed,  or  are  expressed  by  a  new  con- 
ventional gestui'e  language. 

Anarthria. — If  the  lesion  is  situated  somewhat  lower  in  the  corona  radiata,  in 
the  vicinity  of  the  internal  capsule,  it  is  no  longer  apliasia,  but  anarthria  or 
dysarthria  which  is  observed  (defect  of  articulation). 

3.  Trans-cortical  aphasia.— In  trans-cortical  aphasias,  all  the  verbal  images 
persist,  but  their  mutual  sensory  or  motor  connexion  can  no  longer  be  definitely 
effected.  Hence  it  follows  that  certain  varieties  of  automatic  language  are  affected 
(reading  aloud,  repetition,  ordinary  copying,  or  copying  from  dictation).  Con- 
scious voluntary  speech  is,  on  the  contrary,  possible  by  means  of  the  both  indirect 
and  complicated  connexions  formed  between  the  sensorial  and  motor  images. 

4.  Supra-cortical  aphasias. — In  the  aphasias  known  as  supra-cortical  verbal 
images  still  persist,  they  are  renewed  and  expressed  by  means  of  the  connexions 
maintained  with  the  peripliery,  and  are  mutually  evoked  (from  the  sensorial  to 
the  motor)  in  automatic  language  ;  but  connexions  of  a  slightly  different  natm-e 
are  then  partially  interrupted.  The  passage  from  the  image  to  the  idea,  or 
conversely  from  the  idea  to  the  image,  in  any  one,  or  in  several,  forms  of  sensation 
has  become  difficult  or  impossible.  The  idea  exists  and  also  the  image,  hut  the  one 
cannot  call  up  the  other,  or  conversely. 

Seat  of  ideation. — The  most  ill-defined  centre,  anatomically  and 
functionally,  is  that  known  as  the  centre  of  ideation,  which  is  repre- 
sented in  most  schemes,  including  that  of  Charcot,  as  being  isolated 
from  the  others.  It  seems  to  me  that  the  expression  "  centre  "  should 
be  here  especially  considered  as  being  purely  symbolical.  Less  than 
any  other,  can  the  function  of  "  intelligence  "  be  concentrated  and 
localized  in  a  definite  region  of  the  brain  (for  example,  in  the  frontal 
lobe). 

Doubtless,  when  substituted  for  the  psychological  automatism,  it  is 
brought  into  being  in  the  cerebral  cortex  by  an  extension  of  already 
associated  systems,  which  in  the  aggregate  includes  new  portions  and 
new  systems,  solidarized  into  a  complex  association  ;  but  we  are  not 
authorized  in  maintaining  that  these  superadded  systems  (which  may 
be  called  supra-cortical  centres)  would  subserve  the  intellectual  func- 
tion were  they  completely  isolated.  Further,  the  conception  of  a 
centre  of  ideation  is  only  brought  forward  for  the  purpose  of  simplifying 
and  classifying  facts. 

Automatism  and  intelligence. — It  is  certain  that,  in  apparently  similar  dis- 
turbances of  language,  intelligence  inay  be  affected  in  a  somewhat  diverse  manner. 


LANGUAGE    AND    IDEATION 


669 


Much  diminished  in  some  eases,  it  may  be  left  ahiiost  intact  in  others.  We  liave 
said  above  that,  in  aphasias  of  conductivity,  it  is  much  better  preserved  than  in 
aphasias  the  result  of  cortical  destruction,  the  mechanism  being  much  less  in- 


volved in  the  first  than  in  the  second, 
observed  between  intelligence  and 
speech,  the  latter  being  automatic 
and  effected  without  comprehension 
of  the  words  spoken,  intelligence 
nevertheless  being  manifested  in 
an  indubitable  manner. 

There  is  then,  in  this  case,  a 
separation  between  external  lan- 
guage (become  automatic)  and  in- 
ternal language  (which  represents 
ideation).  It  is  scarcely  jjossible  to 
maintain  that  this  fvmctional  dis- 
sociation corresponds  to  a  total  isola- 
tion of  the  seat  of  ideation,  which 
would  then  be  left  without  any  con- 
nexion with  the  exterior.  In  such  a 
case  intelligence  would  be  necessarilj' 
and  very  seriously  affected  ;  it  is 
much  less  so  when  one  of  the  areas 
for  the  formation  of  verbal  images, 
auditory  for  example,  is  destroyed. 
In  tlie  aphasias  by  default  of  con- 
duction, and  especially  in  those 
called  supra-cortical  (supra-poly- 
gonal according  to  the  diagi'am),  it 
would  seem  that  the  connexion  be- 
tween the  different  partial  areas  of 
language  is  less  gravely  involved 
than  in  cortical  aphasias,  although 
certain  ways  of  passing  from  tlie 
word  to  the  idea  and  from  the  idea 
to  the  word  become  impossible. 
By  the  fact  of  this  connexion  being 
less  disturbed,  the  preservation  of 
internal  language  and  of  more  com- 
plete ideation  in  these^  forms  of 
aphasia  may  be  explained.  Whence 
it  follows  that  it  is  this  connexion, 
together  with  probably  an  extension 
of  the  associations  in  the  cerebral 


Sometimes  a  kind  of  dissociation  may  be 


Fig.  •262. — Centres  or  systems  of  language 
and  their  principal  associations. 

A,  auditory  centre  ;  V,  visual  centre  ;  M, 
motor  centre  of  speech  ;  E,  motor  centre  of 
writing  ;    00,  intellectual  centre. 

Sensory  nerves  in  blue ;  aN,  auditory 
nerve  ;  vV,  optic  nerve.  Motor  nerves  in 
red  ;  Mw,  nerves  of  phonation  ;  Ee,  nerve 
of  writing  (after  Grasset). 


substance,  which  forms  the  essential  condition  of  ideation. 

3.  The  area  of  language,  its  constitution 
Anatomical  and  clinical  analysis  has,  as  we  have  seen,  defined  three 
partial  areas  in  the  cortex  (three  centres)  :  one  for  auditory,  one  for 
visual,  and  one  for  motor  images  of  phonation,  and  yet  another,  a 
fourth,  if  we  include  the  centre  for  writing  ;  to  all  these  areas  distinct 
functions  as  regards  language  have  been  attributed,  and  they  were 
formerly  considered  as  being  independent. 


670 


SPECIAL    INNERVATIONS 


The  subsequent  investigations  of  Freud  and  Miraille  have  tended, 
while  upholding  their  functional  differences,  to  point  out  the  connexions 
which  these  areas  maintain  between  themselves,  and  also  with  the 
neighbouring  areas  of  the  cortex.  These  authors  maintain  the  existence 
of  an  area  of  language,  of  which  the  centre  for  motor  images  (base  of 
the  third  frontal)  occupies  the  anterior  portion,  the  centre  for  verbal 
auditory  images  (first  temporal)  the  postero-inferior  portion,  the  centre 
of  verbal  visual  images  (jjarietal  lobule  and  angular  gyrus)  the  postero- 
superior  j^ortion.  These  centres  are  mutually  connected  by  fibres  of 
association,  which  thus  make  of  them  a  complex  whole,  so  that  the 
individual  lesion  of  each  involves  a  general  disturbance  of  all,  but  with 
marked  predominance  in  the  function  corresponding  to  the  centre 


Fig.  263. — Area  of  language  and  its  three  centres  of  images  (after  Dejerine). 

A,  centre  of  the  auditory  images  of  words  (centre  of  Wernicke)  ;  B,  centre  of  the  motor  images 
of  articulation  (centre  of  Broca)  ;  Pc,  centre  of  the  visual  images  of  words. 
A  dotted  line  indicates  the  limits  of  the  area  of  language  as  a  whole. 

affected  by  the  lesion.  They  also  observe  that  each  of  these  centres  is 
in  direct  relation  with  an  area  of  the  cortex,  which  acts  as  a  storehouse 
for  general  impressions  belonging  to  the  same  category.  Broca's 
centre  is  in  contact  with  the  general  motor  area,  at  its  inferior  portion, 
in  the  vicinity  of  the  cortical  origins  of  the  hypoglossal  nerve,  the 
facial  nerve,  and  the  nerves  supplying  the  muscles  of  mastication 
(nerves  of  the  face,  the  lips,  the  soft  palate,  the  tongue,  the  larynx  and 
the  pharynx).  The  centre  for  visual  images  is  connected  with  the 
centre  of  general  vision  by  its  deep  surface,  and  comes  in  contact  with 
the  optic  radiations.  The  centre  for  auditory  images  is  almost  identical 
with  that  of  general  audition.  In  short :  according  to  this  theory 
e  ach  centre  is  a  portion  of  the  neighbouring  area,  differentiated  and  apyro- 


LANGUAGE    AND    IDEATION  671 

priated  to  the  specialized  function  of  language.  As,  on  the  other  hand, 
the  connexion  between  these  different  sensorial  and  motor  centres  is  a 
close  one,  isolated  lesion  of  each  of  them  is  rendered  evident  by  predomi- 
nating disturbances  of  its  oivn  proper  function,  and  these  also  react,  but  in 
a  feebler  manner,  on  the  functiojis  of  the  other  centres  (Dejerine). 

Fibres  of  association. — Of  the  fibres  of  association  of  the  area  of  language  some 
are  short,  passing  from  one  convolution  to  another,  and  others  are  lo7ig,  uniting 
this  to  other  cortical  areas.  Amongst  them  may  be  defined  a  superior  longitud- 
inal or  arched  tract  :  an  occipito-frontal  tract  extending  between  the  frontal  lobe, 
the  insula,  and  the  temporo-occipital  lobe  (forms  the  tapetutn)  ;  an  inferior 
longitudinal  tract  wliich  unites  the  visual  occipital  area  to  the  temporal  lobe. 
The  area  of  one  side  is  united  to  that  of  the  other  by  the  inferior  portion  of  the 
body  of  the  corpus  callosum. 

Fibres  of  projection. — From  the  area  of  language  fibres  of  projection  extend  to 
the  optic  tlialamus.  A  fronto-thalamic  tract  occupies  the  anterior  segment  of 
the  internal  capsule.  The  fibres  of  the  third  frontal  convolution,  and  of  the 
adjacent  region,  form  the  knee  of  the  internal  capsule  (anterior  portion  of  its 
posterior  segment)  ;  in  the  crusta  (pied)  of  the  crus  cerebri  they  occupy  the 
antero-internal  and  the  internal  border. 

C.     PROCESSES  AND  ORGANS  OF  ASSOCIATION 

Experimental  and  clinical  analj'sis  when  applied  to  the  brain  proves  the  exist- 
ence of  an  obvious  functional  diiTcrentiation  between  its  different  portions.  The 
removal  of  certain  determinate  areas  of  tlie  cortex  abolishes,  or  at  least  degrades, 
specific  systems,  the  activity  of  which  altogether  ceases  or  becomes  vmrecog- 
nizable.  An  impvdse,  when  artificially  caused  to  penetrate  these  areas,  re- 
awakens this  activit}-,  and  renders  it  manifest  by  motor  effects.  These  terri- 
tories, however,  such  as  they  have  been  delimited  by  exjjeriment,  are  not 
continuous,  but  leave  between  them  a  space  of  irregular  outline,  to  which  the 
name  of  latent  or  inexcitable  area  has  sometimes  been  given.  As  is  obvious,  it 
is  more  especially  by  its  negative  characters  that  this  distinct  territory  is  defined. 
Its  destruction  does  not  involve  sensory  or  sensorial  anaesthesia,  and  does  not 
bring  about  a  motor  paralysis  ;  and  its  stimxilation  is  not  revealed  by  any 
externally  visible  signs. 

Anatomical  hypothesis. — The  alternative  lies  between  the  following  hj'po- 
theses  :  either  this  area  described  as  inexcitable  is  fundamentally  equivalent  to 
those  which  crown  the  sensorial  systems  known  as  specific,  only  its  senso- 
motricity  is  of  an  order  which  we  are  incapable  of  recognizing  ;  or  else  it  clearly 
differs  from  those  appertaining  to  these  specific  systems  and  presides  over  func- 
tions into  which  the  diverse  sensibilities  and  motricities  no  longer  enter  as  distinct 
and  recognizable  elements,  but  are,  on  the  contrary,  mingled  together  in  different 
ways. 

The  second  of  these  two  hypotheses  is  the  one  which  has  had  the  widest  accept- 
ation. A  support  for  it,  and  in  a  sense  a  demonstration  of  it,  has  been  fomid  in 
the  anatomical  fact,  first  affii-med  by  Flechsig,  that  tliis  inexcitable  area  (itself 
decomposable  into  a  certam  number  of  special  areas),  being  deprived  of  fibres 
of  projection,  is,  on  the  other  hand,  rich  in  fibres  of  association,  both  long  and 
short,  which  bring  it  into  connexion  with  the  specific  areas  of  the  different  senses. 
In  a  word,  its  function  would  thus  be,  not  to  associate  the  cortex  with  the  func- 
tional activity  of  the  grey  axis,  in  motor  or  sensorj*  transmissions,  but  to  connect 
the  sensori-motor  cortical  areas,  and  in  this  way  to  derive  from  them  new  mani- 


672  SPECIAL    INNERVATIONS 

festations  of  a  superior  psychism.  So  these  territories,  which  make  no  response 
whatever  to  direct  stimulation,  would  be  centres  of  ideation. 

Objections. — The  anatomical  fact  brought  forward  by  Flechsig  has  been 
strongly  criticised  by  several  authors  (C.  and  O.  Vogt,  Mahaim,  Sachs,  Dejerine, 
Monakow),  and  has  been  also  partly  abandoned  by  himself. 

Experiments, — Demoor  has  striven  to  clear  up  this  question  by  the  following 
experiments.  He  destroys  the  cerebral  cortex  in  different  dogs  in  the  following 
manner  :  (a)  in  the  tactile  area  (sigmoid  gyrus)  ;  (b)  in  the  visual  area  (occipital 
lobe)  ;  (c)  in  the  frontal  lobe  ;  {d)  in  the  parietal  lobe  (these  two  latter  regions 
being  described  as  centres  for  the  association  or  the  formation  of  ideas,  by  com- 
parison with  the  two  former, which  represent  centres  of  projection).  The  results 
observed  (symptoms  of  deficiency  after  cure)  have  been  as  follows  : — 

a.  Ablation  of  the  tactile  area. — Sensibility  and  motricity  persist  with  the 
essential  modifications  observed  in  such  cases.  The  character  is  changed,  and 
the  animal  becomes  aggressive.  Intelligence  is  absolutely  ruined.  Neither  by 
touch,  hearing,  sight  nor  smell  can  the  animal  be  induced  to  perform  any  intelli- 
gent act  ;    it  may  be  considered  as  being  in  a  condition  of  dementia. 

b.  Ablation  of  the  visual  area. — First  of  all,  psychical  blindness  appears  (cortical 
blindness),  then  vision  becomes,  after  a  certain  time,  at  least  partially  re-estab- 
lished. The  dog  then  presents  a  normal  appearance  and  is  capable  of  the  educa- 
tion or  intellectual  acquisitions  of  an  ordinary  dog. 

c.  Ablation  of  the  frontal  centres. — Except  for  a  slightly  increased  excitability, 
which  disappears  after  some  days,  no  change  from  the  normal  condition  can  be 
noticed. 

d.  Ablation  of  the  parietal  centres. — When  in  a  locality  which  is  known  to  it, 
the  animal  appears  to  be  in  a  normal  condition  ;  but  it  presents  serious  anomalies 
when  in  an  unfamiliar  place  ;  it  experiences  great  difficulty  in  ascending  a  stair- 
case and  is  incapable  of  descending  ;  it  is  also  incapable  of  learning  how  to  "  give 
a  paw.'' 

From  the  last  experiment  the  author  infers  that  the  parietal  centre  really 
possesses  a  function  of  association  of  the  nature  of  that  which  has  been  attributed 
to  it  ;  it  would,  then,  in  the  dog  be  the  co-ordinating  centre  of  the  elementary 
intellectvial  activities.  The  frontal  centre  has  only  very  slight  influence,  and 
that  not  a  recognizable  one,  this  being  the  result  of  its  very  rudimentary  develop- 
ment in  the  carnivora  ;  this  centre  being  phylogenetically  (and  ontogenetically) 
of  very  tardy  development,  and  only  acquiring  importance  in  the  primates  and 
more  especially  in  man. 

It  must  be  observed  with  regard  to  this  subject  that  the  frontal  lobe  of  the 
xingulata  is  highly  developed  in  comparison  with  that  of  the  carnivora,  and  this 
obviously  without  the  intelligence  of  these  animals  profiting  from  this  develop- 
ment (Monakow). 

I  With  regard  to  the  parietal  centre,  we  cannot  help  remarking  that,  if  its  destruc- 
tion has  brought  about  a  disturbance  in  the  association  of  ideas  and  intelligence, 
this  disturbance  is  incomparably  less  marked  than  that  resulting  from  the  destruc- 
tion of  the  tactile  area  ;  and  yet,  in  the  latter  case,  the  animal  retained  not  only 
its  parietal  and  frontal  centres  of  association,  but  four  out  of  five  of  its  senses 
remained  to  furnish  it  with  sensations,  two  of  them  being  superior  senses,  namely, 
sight  and  hearing. 

Moderating  functions  of  the  frontal  lobe. — Bianchi,  as  the  result  of  the  removal 
of  the  pre-frontal  region  in  the  monkey,  maintains  that  a  certain  condition  of 
mental  inferiority  ensues.  The  experiments  of  this  author,  those  of  Goltz  on 
the  dog,  and  an  observation  of  Harlow  on  man,  all  tend  to  show  that  destructions 
affecting  the  anterior  portion  of  the  brain  produce  a  modification  of  character, 
causing  it  to  become  impulsive,  irritable,  and  incapable  of  exerting  self-control. 


LANGUAGE    AND    IDEATION  673 

Inhibition. — R.  Oddi,  and,  later,  G.  Fano,  operating  on  the  dog,  have  proved 
tliat  stimulation  of  the  frontal  area,  which  is  considered  inexcitable,  has  an  in- 
hibitory influence  on  the  movements  elicited  by  reflex  stimtilation.  Fano,  after 
ablation  of  the  cortex  in  this  region,  finds  that  the  latent  period  of  the  reflexes 
is  diminished.  This  is  more  especially  a  crossed  action,  and  one  more  obvious 
in  the  anterior  tlian  the  posterior  limb.  As  regards  the  first,  the  time  occupied 
by  the  reflex,  which  is  from  32-6  to  36'9  thousandths  of  a  second,  becomes,  some 
daj-s  after  the  operation,  23'8  to  26"  1  thousandths  of  a  second. 

In  spite  of  then-  interest,  these  facts  throw  but  a  feeble  light  on  the  function  of 
the  brain  taken  as  a  whole.  Apart  from  a  fvmctional  differentiation  wliich  affects 
certain  of  its  regions  and  of  the  links  which  unite  certain  specific  territories  in 
the  area  of  language,  it  must  be  admitted  that  we  know  very  little  concerning 
this  function. 


D.     SLEEP. 

Sleep  is  a  suspension,  a  more  or  less  complete  interruption,  of  conscious  and 
voluntary  activity.  The  external  senses  are  partially  closed,  or  are  voluntarily 
sheltered  from  stimuli  arising  from  the  external  world.  The  body  assumes, 
preferably,  a  horizontal  position  and  remains  almost  motionless.  The  respiration, 
the  circulation  (slightlj'  slowed)  and  the  general  nutritive  activity  pursue  theii* 
regular  course.  The  eyelids  are  closed,  and  the  pupils  being  contracted,  the  eyes 
are  turned  upwards  and  inwards. 

Dreams. — Mental  activity  is  not  entirely  aboHshed  ;  the  occui-rence  of  dreams, 
many  of  which  leave  a  more  or  less  distinct  impression  in  oiu*  memory  (often 
very  slight,  and  no  doubt  frequently  entirely  effaced)  is  a  proof  of  this  being  so. 
Mental  activity  in  dreaming  is  based  on  previous  excitations  of  the  nervous 
system,  which  have  remained  stored  up  in  it  in  an  unconscious  state,  and  to  which, 
diu-ing  sleep,  are  added  the  slight  excitations  accidentally  arising  from  the  senses 
in  spite  of  their  state  of  repose  (external  noises,  pressure  of  the  body  on  the  skin 
and  the  limbs,  internal  excitations  having  their  source  in  the  viscera,  etc. ).  When 
awake,  these  sensory  or  sensorial  excitations  are  superposed  to  previous  residual 
excitations  of  the  same  natvu"e,  which  they  recall  in  a  logical  order,  according  to 
certain  laws.  In  dreaming,  on  account  of  the  lowering  of  the  cerebral  activity 
whicli  is  essential  to  sleep,  these  associations  are  foriued,  as  it  were,  haphazard, 
whence  arises  their  instability,  as  well  as  the  well  kno^vn  extravagance  and  in- 
coherence of  dreams  (Bergson). 

Supposed  mechanism. — With  regard  to  the  manner  in  which  the  disaggregation 
of  cerebral  systems  is  brought  about  in  sleep  and  their  recomposition  on  waking, 
several  hj'potheses  have  ^been  formed,  some  of  a  chemical  order  (ponogenic 
substances  of  Preyer),  others  of  an  anatomical  nature  (histological  tlieory  of 
M.  Duval).  Xevertheless,  the  mechanism  of  sleep  is  still  obscLU-e  and  but  little 
is  known  concerning  it.  During  sleep  the  brain  is  relatively  angemic,  so  far  as 
can  be  judged  from  observations  made  in  men  and  animals  who  have  been 
trephined. 

Necessity  of  sleep. — The  cause  of  sleep  is  also  quite  luiknown  to  us.  The 
nervous  system  is  obedient  to  a  law  of  periodicity  which  is  imposed  on  the  func- 
tions of  all  the  organs  and  of  their  component  elements,  a  law  of  which  we  can 
only  declare  the  general  application,  but  whose  fundamental  natxu'e  is  unknown 
to  us.  Activity  calls  for  repose,  and  reciprocally.  The  period  of  this  activity 
followed  by  repose  is  modelled  on  the  nycthemeron  ;  the  time  of  wakefulness 
corresponding  to  day,  and  that  of  sleep  to  night. 

Artificial  sleep. — Sleep  may  be  obtained  artificially  by  the  aid  of  certain 
substances,  the  narcotics  (morphine),  the  anaesthetics  (chloroform,  ether,  etc.). 

P.  XX 


674  SPECIAL    INNERVATIONS 

Hypnotism. — Iri  individuals  manifesting  hysterical  symptoms  (anaesthesia,  . 
hyperaesthesia,  etc.),  the  condition  called  hypnotism  is  easily  induced  by  stimula- 
tions directed  to  certain  senses,  such  as  passes  made  with  a  magnet,  fixation  of 
the  eyes  on  a  brilliant  object,  pressure  on  certain  points  of  the  cutaneous  surface, 
etc.  Re-awakening  is  obtained  by  similar  means  (blowing  on  the  forehead, 
pressures  .   .   .). 

The  individual  passes  generally  through  three  phases,  which  may,  however, 
sometimes  occur  separately,  namely  :  the  cataleptic,  the  lethargic,  and  the  som- 
namhulistic  condition.  In  this  latter  condition  the  individual  deprived,  in  a 
sense,  of  his  ordinary  personality,  presents  a  really  remarkable  automatism,  and 
obediently  follows  all  suggestions  proposed  to  him,  even  when  these  imply  the 
performance  of  acts  taking  place  at  a  more  or  less  remote  date,  and  which  must 
be  carried  out  after  his  awakening.  Hypnotism,  magnetism,  or  Braidism,  consist 
in  conditions  involving  a  mental  de^Dression  or  resolution,  which  causes  the 
elimination  of  the  superior  functions  of  the  nervous  system,  including  distinct 
consciousness,  and  more  especially  will,  and  only  permitting  the  persistence  of 
an  activity  which  is,  in  a  sense,  purely  automatic. 

Personality  ;  its  disaggregations.- — Hypnosis,  inasmuch  as  it  is  a  condition 
which  can  be  elicited  at  will  in  some  hysterical  subjects,  has  to  some  extent 
rendered  possible  the  analysis  of  psychical  phenomena.  It  proves  that  the  ego 
is  an  association  of  differentiated  and  co-ordinated  elements  (Ribot,  Binet,  Janet). 
This  association  does  not  occupy  the  whole  of  the  organism,  nor  the  whole  of  the 
nervous  system,  but  only  a  portion  of  it.  It  is  not  stationary,  bvit  eminently 
mobile  and  variable.  It  seizes  without  cessation  on  new  elements,  and  eliminates 
others  from  its  constitution. 

Secondary  personalities. — The  elements  which  it  leaves  outside  itself  form 
secondary  aggregations  whose  own  individuality  is  unrecognizable,  lost  as  they 
are  in  the  general  function  in  which  they  co-operate,  although  remaining  external 
to  consciousness  properly  so  called.  In  hypnosis  these  aggregations  are  capable 
of  attaining  a  degree  of  organization  which  brings  them  into  a  condition  of 
secondary  personalities  co-existing  with  the  ego  properly  so  called,  and  quite 
distinct  from  it. 

The  sub-ego  thus  constituted  hears  questions  which  the  ego  does  not  perceive, 
and  returns  answers  to  them  of  which  the  latter  is  unconscious.  The  sensori- 
motor cycle  of  this  special  language  may  be  retained  in  the  tactile  system 
(cutaneous  stiiTuili  or  communicated  movements  initiating  in  answer  intentional 
co-ordinated  movements  of  the  hand)  ;  or  it  may  be  more  extended  (words 
whispered  in  the  ear  giving  rise  to  written  answers  in  persons  whose  attention  is, 
on  the  other  hand,  closely  concentrated  on  a  distinct  object  or  subject). 

Spiritualism. — The  dissociation  of  the  personality  may  in  certain  cases  be 
less  deeply  seated.  The  question  proposed  inay  be  known  by  the  ego  and  be  a 
conscious  one,  and  the  answer  of  the  sub-ego  be  unconscious  and  involuntary ; 
that  is  to  say,  it  may  nevertheless  reveal  an  intelligence  distinct  from  the  pre- 
ceding. This  is  the  case  with  the  mediums  in  those  seances  which  are  called 
spiritualistic.  The  belief  in  extra-somatic  "  spirits,"  which  can  be  called  up 
and  communicate  their  thoughts  through  the  organs  of  the  "  inedium,"  is  founded 
on  facts  of  this  nature.  There  is  usually  in  these  cases  a  separate  intelligence 
(generally  of  an  inferior  order),  which  acts  unknown  to  the  veritable  ego  ;  but 
this  intelligence  occupies  the  saine  body,  the  same  nervous  system,  and  is  nothing 
but  an  alienated  portion  of  the  intelligence  of  the  "  medium  "  which  has  assumed 
an  independent  condition,  but  still  drawing  upon  it  for  a  share  of  the  common 
store  of  memories.  The  separation  is  sometimes  pushed  so  far  that  these  two 
intelligences  may  converse  the  one  with  the  other,  without  foretelling  the  answer, 
as  would  two  organically  distinct  individuals- 


LANGUAGE    AND    IDEATION  675 


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Muscular  sense. — Cattaneo,  Org.  musculo-tendineux,  Arch.  it.  biol.,  1888,  t.  X,  p.  33/. 
— Cl.vpaeede,  Tliese  Geneve,  1897. — Goldscheider,  Arch.  f.  Anat.  u.  Phys.,  1889, 
suppl.,  p.  141.— Ruffini,  Arch.  it.  biol,  1893,  t.  XVIII,  p.  106  ;  Journ.  of  Phys.,  1898, 
p.  100. 

Sensibility  of  the  viscera. — Buys,  Sensib.  de  I'ovaire,  Arch.  it.  biol,  1891,  t.^  XVI, 
p.  87. — Pagano,  Sensib.  du  cceur  et  des  vaisseaux,  Arch.  it.  biol,  1900,  t.  XXXIII. 

Thermic  sensibility. — Cavazzani,  Differenciat.  de  ses  org.  avec  ceux  de  la  pression, 
Arch.  it.  biol,  1892,  t.  XVII,  p.  413. — Goldscheider,  Previves  diverges  dissociation. 
Arch.  f.  Anal  u.  Phys.,  1885,  suppl.  1886,  1887,  1888.— Ch.  Henry,  Sensib.  therm., 
C.  R.  Ac.  sc,  1890.  t.  CXI,  p.  274  ;  Relation  sensib.  thermique  avec  temperature,  C.  R. 
Ac  sc,  1896,  t.  CXXII,  p.  1437. 

Visual  innervation— Retina.— Fr.  Boll,  Abelsdorff  .  .  .  HeUigkeit.  und.  Farbensin, 
Arch.  f.  Ayiat.  u.  Phys.,  1900  ;  Licht  und  Farbenempfindung,  Arch.  f.  Anat.  u.  Phys., 
1881.— Charpentier,  Vision  differ,  parties  retine.  Arch.  Phys.,  1877  ;  Vitesses  des 
reactions,  Ibid.  1883  ;  Sensations  visuelles  et  auditives.  Ibid.,  1890  ;  Dissociat.  impress, 
sensit.  success,  occupant  le  meme  siege.  Ibid.,  1891  ;  React,  oscill.  retine.  Ibid.,  1892  ; 
Oscill.  retinieimes.  Ibid.,  1896  ;  Sens  lumin..  Rev.  gen.  sc,  1898. — J.  Gad,  Energieumsatz 
in  Retina,  Arch.  f.  Anal  u.  Phys.,  1894. — Greeff,  Morphol.  und  Physiol.  Spiiienzellen 
.  .  .  Arch.  f.  Anat.  u.  Phys.,  1894  ;  Langsverbind.  in  der  menschl.  Retina,  i6ic?.,  1898. 
— KoNiG,  Farbenschen  und  Farbenblindheit,  Arch.  f.  Anat.  u.  Phys.,  1885. — Kries, 
Gesichtsempfindmig,  Arch.  f.  Anat.  u.  Phys.,  1878. — Parinaud,  La  \ision  :  le  mcme, 
Rev.  gen.  sc,  1898. — Rawitz,  Cephalopoden  retina.  Arch.  f.  Anat.  u.  Phys.,  1891. 

Chiasma. — Bechterew,  Newol.  Centralbl,  1898. — Cajal,  Rev.  trimest.  micr.,  18C8. 
— GuDDEN,  Graefe's  Arch.  f.  Ophtalm.,  XX,  1874  ;  XXI,  1875,  et  XXV,  1879.— Jacob- 
sohn,  Neurol  Centralbl,  1896  et  1898.— Nigati,  Arch,  de  Phys.,  1878.' 

Hemiopia  ;  hemianopsia. — Dejerine,  Sollier  et  Auscher,  Lesion  ecorce  occipitale, 
Arch.  Phys.,  1890,  p.  17f. — Wernicke,  .  .  .  Reichsettig.  Hemiopie,  Arch.  f.  Anat.  u. 
Phys.,  1878. 

Cortical  visual  sphere. — Monakow,  Ursprvmgcentren  .  .  .  Arch.  f.  Anat.  u.  Phys., 
1885.— H.  MuNCK,  Arch.  f.  Anal,  u.  Phys.,  1879  et  1880. 

Cortical  sphere. — Bechterew,  Neurol  Centralbl,  1897. — Bouveret,  Rev.  gin.  ojht., 
opht.,  et  Lyon  medical,  1877. — Brissaud,  Ann.  ocidist.,  1893. ^Dejerine,  Biologic 
(memoire),  1892. — Henschen,  Congres  internat.  de  Rome,  1894. — Lannegeace,  Arch, 
med.  exper.,]  889. — Luciani  et  Tamburini,  Sui  centri  psico-si  usoricortiali,  Reggio  Emilia, 
1879.— MoNAKOVi%  Arch.  f.  Psych.,  XIV  a  XXlV.— Munk,  Akad.  d.  Wiss.  Berlin,  1890. 
— Schaffer,  Brain,  1888.^Scherrington,  Journ.  of  Phys.,  1894. — J.  Soury,  Les  fonc- 
tions  du  cerveau,  2e  edit.,  1892  (Ind.  bibliogr. ). — Steiner,  Pfiilger's  Arch.,  1891. — 
ViALET,  These  Paris,  1893.— Vitzou,  Arch,  de  Phys.,  1893  et  1897. 

Pupillary  reaction. — E.  Hesse,  Pflvgers  Arch.,  LIL— E.  Leyden,  Deutsche  med. 
Wochenschr.,  1892. — Massaut,  Arch.  f.  Psych.,  XXVIII,  1896. — Mendel,  Berliner 
Iclin.  Woehensch.,  Nov.  1889. 

Auditory  innervation  —  sense  of  hearing;  internal  ear.^ — Beauregard  et  Dupuy, 
Variation  electriq.  nerf  acoustique  excite  par  le  son,  C.  i?.  ..4c.  sc,  1896. — Berthelot, 
Sensat.  acoust.  par  sels  de  quinine,  C.  R.  Ac  sc,  1890. — Bonnafont,  Phen.  nerv.  par 


676  SPECIAL    INNERVATIONS 

pression  membr.  tyinp.,  C.  R.  Ac.  sc,  1882.— Deganello,  Ablat.  can.  demicircul. 
degenerat.  bulbe  et  cervelet,  Arch.  ital.  hiol.,  1899.  —Dixon,  Tomps  de  reaction.  Journ. 
of  Phys.,  1896. — Gaglio,  Anesthesie  can.  demi-circul.,  Arch.  ital.  biol.  1899.— Vulpian, 
Troubles  par  excit.  app.  auditif,  C.  R.  Ac.  sc,  1883. — Wreden,  Electr.  reiz.  ed 
Gehororgans,  Arch,  de  Pfliiger,  1872. 

Sense  of  space. — Bonnier,  Phy,siol.  du  nerf  de  I'espace,  C.  R.  Ac.  sc,  1891  ;  Vertige, 
Bihlioth.  Charcot- Dcbove  ;  Oreille,  Encycl.  aide-memoire. — De  Cyon,  Rapport  nerf 
acoustiq.  et  app.  mot.  de  I'ceil,  C.  R.  Ac.  sc,  1876  ;  Org.  periph.  du  sens  de  I'espace, 
Ibid.,  1877  ;  Bogengange  und  Raumsinn,  Arch.  f.  Anat.  u.  Phys.,  1897  ;  sens  espace, 
C.  R.  Ac.  sc,  1900.— Fred.  Lee,  Equilib.  in  Fisher,  Journ.  of  Phys.,  1894,  1895. 

Cortical  centre  of  audition. — Bechterew,  Gehorcentra,  Arch.  f.  Anat.  u  Phys.,  1899, 
suppl. 

Pure  verbal  deafness. — Dejerine  et  Serieux,  Biol.  1897. — Ideation  ;  largimge. — 
G.  Ballet,  Lang,  interieur. — Binet,  Alterations  de  la  personnalite. — Egger,  Lang, 
interieur. — Grasset,  Etudes  cliniques. — -Janet,  Automatisme  psychologique. — -Taine, 
De  I'intelligence. 

Aphasia. — Broca  .  .  .  Siege  faculte  du  langage,  Soc.  anat.,  1861,  2ine  serie,  p.  3.30, 
Soc  a7ithropol., nAncoT  1863. — C,Progres  medical,  1883,  pp.  23,  27,  521,  859. — Grasset, 
Etudes  cliniques. — Miraille,  Th.  Paris,  1896. — Wernicke,  Arbeit,  ans  psych.  Klin. 
Breslau,  Heft  II,  Leipzig,  1895,  et  Grundrisse  der  Psychiatric  in  Klin.  Vorlesung,  t.  I, 
1894. 


Index 


Abstraction,  653 

Affective  (Tone),  400 

Agraphia,  064 

Amblyopia    through    sensory    antcsthesia, 

563 
Aniteboism,  nervous,  23 
Amimia,  665 
Amusia,  665 
Anartliria,  668 
Anaesthesia,  563 
Anaesthesia,  crossed,  271 
Anaesthetics,  106 
Animal  and  organic  life,  286 
Anosmatics,  634 

Antitonic  (action)  of  the  vagus  nerves,  304 
Apex  of  the  heart,  298 
Aphasia,  cortical,  063  ;    motor,  663  ;  sen- 
sorial, 064      by  default  of  conduction, 

665 
Apparatus    for   electrical    excitation,    55  ; 

for   the   verification  and   estimation   of 

electro-motor  phenomena,  57 
Apparatus,     nervous     sub-dermic,     497  : 

intra-dermic,  498  ;    intra-epidermic,  499 
Arc,  marginal,  external  and  internal,  636 
Areas    of    anaesthesia    of    the    skin,    145  ; 

motor  of  the  brain,  523  ;  sensitive-motor, 

512  ;    of  language,  531,  669 
Areas,  cortical  :     auditory,    622 ;    tactile, 

511;     visual,    566;     vaso-motor,     473; 

motor,  458,  523  ;    motor,  numerous  for 

the  eyes,  592 
Association  of  systems,  122  ;    of  neurons, 

284  ;  processes  and  organs  of  association, 

118,    671;     different    functional,    579; 

fibres  of  association,  671 
Atropine    111 
Attention,  659 

Attitudes  (direction  of  the),  cephalic,  379 
Avidition,  506  ;   auditory  field,  613 
Auditory  (nerve),  167,  615,  616 
Automatism,  psychical,  423,  608 
Avoidance,  17 
Axial  (ctirrent),  77 
Axon,  9 

B 

Balance,  evolutional  and  functional,  559. 

634 
Barking,  532 

Bilaterality  (of  laaovements),  535. 
Binaiu-icular  (audition),  613 
Binocular  (vision),  565 
Blindness,  physical,  573  ;    psychical,  573  ; 

verbal,  574 
Blinking  of  the  eyelids,  355 
Body,  external  genicuUxte,  556  ;    internal, 

618;      pituitary,     644;      pineal,     457; 

restiform,  386 
Braidism,  674 


Brain,  424  ;  luuuan,  432  ;  of  the  primates, 
monkey,  434  ;  of  the  carnivora,  dog, 
435 

Bulb,  rachidian,  347  ;    olfactory,  629 

C 

Calcarine  (Fissm-e),  567 

Calorimetry  (indirect  of  the  brain),  453 

Canals,  semi-circular,  596 

Capsule,  internal,^440  ;  excitation  in  the 
monkey,  538 

Cataleptic  (state),  074 

Cathode,  63 

Cell,  segmentary,  10 ;  nervous,  12  ; 
amacrine,  23  ; ""  basket,  28  ;  mitral,  27, 
030  ;  of  Purkinje,  383  ;  pyramidal, 
429 ;  polymorphous,  430 ;  of  Mar- 
tinotti,  430 ;  bipolar  visual,  554  ; 
acoustic,  006  ;  olfactory,  628  ;  gusta- 
tory, 045 

Centres,  246  ;  of  reflexion,  218  ;  reflex  of 
the  spinal  cord,  225  ;  encephalic  sub- 
cortical, 225  ;  reflex,  cortical,  225  ;  ex- 
citation of  the  centres,  260  ;  determina- 
tion of  the  centres,  200  ;  vaso-motor 
general  bulbar,  304  ;  medullary  and 
ganglionic,  364  ;   cardio-inliibitory,  365 

Cerebellum,  372 

Chemistry,  animal  and  nervous  system, 
25 

Chiasma,  auditory,  617  ;  olfactory,  6-JO  ; 
optic,  564 

Chorda  tympani,  39,  174 

Chromatolysis,  35 

Circulation  of  excitation,  cerebral,  454 

Cocaine,  108 

Cochlea,  006 

Collaterals,  11 

Coluimi,  lateral,  209  ;    antero-lateral,  281 

Commissiu"e,  anterior  of  the  bram,  640 

Comparison,  653 

Condensers,  56 

Conduction,  isolated,  44 

Consciousness,  118,  258,  651 

Conservation  of  the  excitation,  239 

Convergence  of  the  eyes,  356 

Convolution,  man,  433  ;  primates,  434  ; 
dog,  435  ;    Hmbic,  438,  443 

Co-ordination,  cerebellar,  373  ;  spinal,  393 

Comu  Ammonis,  642 

Corona  radiata,  440,  641. 

Corpora,  quadrigemina,  421 ;  anterior, 
580;  and  posterior,  618,  627 

Corpuscles  of  touch,  497  ;   of  Golgi,  542 

Cough,  363 

Cimeus,  567 

Cm-are,  109 

Current  of  repose,  75  ;  axial,  77  ;  elec- 
trotonic,  89  ;  medium,  95  ;  ascending, 
descending,    95 ;     strong,    96 ;     of  high 


678 


INDEX 


frequency,  104  ;  of  entrance  and  exit  of 
the  excitation,  128 
Cycles,  energetic,  G  ;    of    the    niviscle  and 
the  brain,  452 

D 

Deaf-mutism,  G23,  G54 

Deafness,  physical,  psychical,  G23,  G54  ; 
verbal,  664 

Degenerations,  30  ;  Wallerian  or  descend- 
ing, 30  ;  ascending,  30  ;  atrophic,  37  ; 
of  the  cerebellum,  384 

Deglutition,  357 

Deviation,  conjugate  of  the  eyes,  355,  390, 
581 

Dextrogyral,  hemioculo-motor  nerve,  581 

Dispersion  of  the  excitation,  223,  259, 
506,  558 

Dissociation,  apparent  of  sensibihty  and 
motricity,  518 

Doctrines,  myogenic  and  nerv^ogenic,  299 

Dog  (Brain  of),  439 

Dreams,  673 

Dynamogeny,  235 

E 

Effort  (Nerve  of),  204  ;  muscular,  psychic, 
549 

Electricity,  prehminary  notions,  51  ;  dif- 
ferent uses  and  effects,  103  ;  death  by 
electricity,  105 

Electric  (Energy),  52  ;  electi'ic  excitation, 
63 

Electrotonus  (Electrotonic  state),  89  ; 
modifications  of  excitabiHty,  93  ;  in 
man,  97  ;  in  nerves  of  different  func- 
tions,  101 

Emotions,  404 ;  their  expression,  406, 
648  ;  language  of  the  emotions,  40G  ; 
expression  of  on  the  human  face,  407 

Energies  revealed  in  the  nerve,  73  ; 
electric,  75 

Epilepsy,  537  ;  internal,  540  ;  Jacksonian, 
540  ;    from  absinthe,  541 

Epiphysis,  459 

Eqviilibriimi,  its  conditions,  374  ;  chemical, 
251  ;  its  rupture  by  the  nervous  system, 
251 

Excitability  and  conductivity,  42  ;  local 
of  the  different  parts  of  the  neuron,  48  ; 
grey  and  white  matter,  526  ;  variations, 
526 

Excitation  of  the  nerves,  50  ;  electrical, 
its  laws,  58,  63  ;  metliod,  63  ;  vmipolar, 
65  ;  in  open  circuit,  66  ;  periodic,  67  ; 
wave  of  propagation,  79  ;  part  played 
by  the  cell,  84  ;  automatic,  239  ;  of  the 
grey  matter,  260  ;  of  the  cerebellmn, 
394  ;  of  the  optic  thalamus,  415  ;  of  the 
corpus  striatum,  420  ;  of  the  sympa- 
thetic in  man,  456  ;  of  the  nerve  trunks, 
402  ;  of  the  central  masses,  403  ;  of  the 
cerebral  cortex,  403  ;  of  the  motor 
areal  524  ;  vohintary,  55 1  ;  labyrinthine, 
603 
Exteriorization  of  sensation,  521,  572 


Facial  (Nerve),  169;  'superior  and  in- 
ferior, 411 

Fatigue  of  the  nerves,  86  ;  intellectual, 
660 

Fibres,  myelinated  and  non-myelinated, 
10,  294  ;  terminal  and  of  passage  of  the 
ganglia,  296  ;  spiral,  29  ;  alteration  in 
degeneration,  31  ;  of  projection,  527  ;  of 
the  fu'st  and  second  order,  121,  427  ;  of 
the  great  sympathetic,  322 ;  of  pro- 
jection and  of  association,  285,432,  671  ; 
centrifugal  of  the  optic  nerve,  597 

Field,  sensory,  motor,  136,  277  ;  electrical, 
magnetic,  54,  103 

Foetus  (sensibility  and  movements  of), 
552 

Function  of  internal  or  trophic  connexion, 
30  ;  of  external  or  nervous  connexion, 
39  ;  of  the  nerve  roots,  124  ;  thermo- 
regulative,  474  ;  baresthesic,  044  ;  man- 
scsthesic,  605  ;    seissesthesic,  606 

G 

Galvanotropism,  103 

Ganglia  of  the  great  sympathetic,  297  ; 
of  the  heart,  298  ;  spinal,  their  passage 
by  the  impulse,  504  ;  of  the  base  of  the 
brain,  397  ;  of  the  haljenula,  637  ; 
spiral  or  of  Corti,  616  ;  vestibular  or 
of  Scarpa,  616  ;  of  Gasser,  182  ;  oph- 
thalmic, 181  ;  geniculate,  165  ;  of 
Andersh,  jugular,  plexiform,  165  ;  otic, 
spheno-palatine,  sub-maxillary,  185 

Geniculate  (Tract),  442,  527,  532,  538,  670 ; 
ganglion,  166 

Geniculate  bodies,  external,  internal,  528 

Globus  pallidus,  excitation  of,  474 

Glomerulus,  olfactory,  629 

Glosso-pharyngeal  (Nerve),  185 

Gradation  of  the  grey  masses,  556 

Gyrus,  angular,  568 

H 

Heat  in  the  nerves,  75  ;    in  tlie  brain,  454  ; 

and  thought,  454 
Hemiansesthesia,  alternate,  352 
Hemianopia,  homonymous,  563 
Hemiplegia,  alternate,  352 
Hemisection  of  the  spinal  cord,  270,  281 
Hypnosis,  674 
Hypoglossal  nerve,  204 
Hypophysis,  456 


Ideation,  648  ;  seat,  608 

Idea,  119 

Images,  consecutive,  564  ;  psychical,  571  ; 
of  objects,  verbal,  653 

Immunity,  electrical,  104 

Impolarizables  (Electrodes),  58  ;  bat- 
teries, 53 

Indifferent  (Pole),  65 

Individuality  of  the  neuron,  19 

Induction,  electrical,  dynamic,  54  ;  ner 
vous,  45 

Influence,  polar,  64 


INDEX 


679 


Inhibition,  227  ;  cardiac,  195  ;  pulmonary, 
194  ;  anodic,  304  ;  pancreatic,  3I(i  ; 
vascular  by  the  great  sjTiipathetic,  364  ; 
secretory,  319  ;  of  the  optic  tlialamus  by 
the  cerebral  cortex,  415  ;  of  the  muscles 
of  the  eye,  587  ;  in  the  invertebrata, 
312  ;   cerebral,  frontal  lobe,  072 

Instinct,  its  characters,  421 

Integrity  of  structiu-e,  47 

Irreversibility  of  the  reflex  cycle,  221 


Kinsesthesic  or   cinsesthesic  (impressions), 

541 
Knowledge,  119,  650 


Labyrinth,  603 

Lancisi  (Strise  or  nerves  of),  641 

Language,  648  ;  automatic,^656  ;  internal, 
656 

LarjTix  (Movements  of  the),  472 

Latent  (Tune),  49 

Laws  of  Waller,  33  ;  electrical  excitation, 
63;  of  contraction,  98;  of  Ritter- 
VaUi,  100 ;  of  Magendie,  128  ;  of 
Pfliiger,  223 

Lethargic  (State),  674 

LevogjTal  nerve,  581 

Life,  animal  and  organic,  286 

Limbic  (Convolution),  633 

Link  (Function  of )  internal,  30;  external, 
39 

Localizations,  cerebral,  457  ;  in  conscious- 
ness, 458  ;  in  luiconsciousness,  471  ; 
cortical  of  sensation,  511  ;  of  motricity, 
523  ;  of  the  muscular  sense,  of  cinaes- 
thesic  impressions,  548  ;  of  the  function 
of  language,  661 

Locomotor  (Functions),  pons,  360  ;  of  the 
corpus  striatvmi,  417 


M 

Magendie  (Laws  of),  128 

Magnetic  (Field),  103  ;  (Induction),  54  ; 
(State),  674 

Mastication,  536 

Matter,  grey,  excitation  of, -260  ;  import- 
ance of  in  sensory  transmission,  275  ;  in 
motor  transmission,  282  ;  of  the  ganglia, 
294  ;   of  the  brain,  its  stimulation,  526 

Metamerism,  143  ;  radicular,  spinal,  144  ; 
cranial,  157  ;  ganglionic,  spinal,  322  ; 
cerebral,  528 

Motricity,  reciu-rent,  135 

Movements  of  the  pupil,  365  ;  of  rotation, 
389 ;  of  the  intestine,  476  ;  of  the 
bladder,  489  ;  of  the  eyes,  of  the 
tongue,  535  ;  of  the  larynx,  536  ;  of 
the  foetus,  552  ;  associated,  580  ;  of  the 
eyes  (their  connexion  \vith  the  muscles), 
584  ;  others  of  the  eyes,  590  ;  of  the 
eyeUds,  590 ;  of  the  head,  591  ;  of 
spoken  and  -written  language,  654 ; 
primary  and  secondary,  530 


N 

Nape  (Movements  of  the),  525 

Xerves,  sensory  and  motor,  243  ;  mixed, 
150 ;  thermic,  247  ;  trophic,  248  ; 
spinal,  143  ;  cranial,  154  ;  sensorial, 
165  ;  sensory  and  motor  cranial,   168 

Ner\'i  nervorum,  598 

Xeurite,  14 

Xeixrons,  static  state,  external  characters, 
8 ;  indi\aduality,  19 ;  specificity,  21, 
490 ;  dynamic  state,  functions,  29  ; 
initial,  terminal,  242 ;  intermediary, 
243  ;    excitatory,  inhibitorj',  244 

Xodus  cursorius,  420 

Xon-polarizable  electrodes,  element,  58 

Nucleus,  red,  382 

Xuclei  of  the  pons,  388 

O 

Objects  (Formation  of  the  images  of),  652 

Observation,  internal  and  external,  649 

Oculo-dextrogjTal  and  oculo-levogyral 
(Xerve),  581 

Oculo-motor  (Xerve),  168,  583 

Oculo-motor,  external  (Xerve),  168 

Olfaction,  628 

Ohves,  388  ;    bulbar,  388  ;    pontine,  389 

Optic  (Xerve),  167 

Organs,  genital,  480 

Organization  and  sensibility,  2  ;  of  energy, 
6  ;   nervous,  120 

Orientation  and  equilibrium,  372  ;  objec- 
tive and  subjective,  611 

Osmatics,  634 

Otocvsts,  602 

Otolyths,  602 

Overlapping  of  the  polar  field,  285 


Pain,  400,  500,  508 

Pairs,  nerve,  125  ;  physiological  charac- 
ters, 158 

Paralysis,  btilbar  and  psevido-bulbar,  537  ; 
of  the  vokuitary  function,  412  ;  of  the 
emotional  expressions,  413 

Parah-tic  (Secretion)  of  the  pancreas,  316 

Pathetic  (Xerve),  169 

Peduncles,  cerebellar,  385  ;    cerebral,  445 

Persistence  of  the  impressions,  tactile, 
502  ;    retinal,  564  ;    auditory,  614 

Personality,  its  disaggregations,  674 

Pilocarpine,  111 

Pleasvire,  400 

Pneumogastric  (Xerve),  188 

Points,  identical,  of  the  retina,  562 

Poisons,  general,  106  ;   special,  109 

Polarization,  djniamic,  15  ;   electrical,  53 

Poles,  active,  indifferent,  65 

Power,  tonic,  309;  reflex,  311:  inhibi- 
tory, 311 

Primates  (Brain  of  the),  434 

Prolongations,  cellulipetal  and  cellulifugal, 
13 

Propagation  in  the  two  directions,  46  ; 
(Rate  of),  49  ;    of  electrotonus,  90 

Piuactvu-e,  diabetic,  367 

Pupil  (Movements  of  the),  365,  417,  578 


680 


INDEX 


Putamen,  420,  421 

Pylorus  (Movements  of  the),  470 


Quadrigemina,  (Corpora),  421  ;  anterior, 
578  ;   posterior,  617,  627 

R 

Rachidian  (Nerves),  143 

Radiations  (Optic),  556 

Recognition,  119,  648 

Recurrent  (Nerve),  191,  203 

Recurrent  (Sensibility),  132  ;  (Motricity), 
135 

Reflexes,  211  ;  localized,  215  ;  classification, 
224  ;  of  the  spinal  cord,  225  ;  subcorti- 
cal, 225 ;  cortical,  225 ;  in  pathology,  226 ; 
the  cerebeUum  and  its  reflex  move- 
ments, 381  ;  tendons,  cutaneous  (red 
nucleus),  382  ;  psycho-reflex  or  sensory 
acts,  398  ;  reflex  cry,  355  ;  .defensive, 
363  ;  vaso-motor,  364  ;  irido-dilatory, 
365  ;  irido-constrictor,  366  ;  bulbar, 
510  ;  retino-pupillary,  365  ;  hemiopic, 
580 ;  of  accommodation  and  of  con- 
vergence, 580  ;  of  visual  protection, 
591  ;  of  adaptation  of  the  olfactory 
paths,  643  ;   of  gustation,  647 

Refractory  (Phase),  300 

Regeneration,  37 

Repose,  compensatory,  300 

Representations,  652 

Retina,  554  ;  (Impressions  on  the),  560  ; 
cortical,  568 

Rheotomes,  57 

Riband  of  Reil  (fillet),  352;  cortical, 
442  ;    of  Vicq  d'Azyr,  568 

Roots  of  the  nervous  system,  124  ;  pos- 
terior, their  mixed  functions,  141 

S 

Sensation,  simple,  118  ;    complex,  118 

Sense  of  ec|uilibriuni,  378  ;  stereognostic, 
503  ;   muscular,  544  ;   of  space,  625 

Sensibility,  1  ;  its  relations  with  move- 
ment, 117,  124;  reciprocal  influence, 
131  ;  recurrent,  132  ;  gustatory  of  the 
chorda  tjmipani,  176;  gastric,  197;  in 
the  spinal  cord,  260  ;  of  the  great  sym- 
pathetic, 339  ;  in  the  medulla  oblongata, 
349  ;  in  the  internal  capsule  and  the 
crura  cerebri,  445  ;  muscular,  544  ; 
osseous,  546  ;    articular,  547 

Sensorium,  common,  359 

Sleep,  indviced,  673 

Sneezing,  363 

Somnambulism,  674 

Space,  bare,  furnished,  572  ;  sense  of 
space,  607  ;  notions  of  space,  relations 
with  the  cortex  and  the  different  senses, 
652 

Specificity  of  the  nevirons,  21,  490  ;  of  the 
stimulus,  488  ;  of  the  sensation,  489  ; 
of  the  sensorial  systems,  491 

Specific  (Innervations),  488 

Spinal  accessory  (Nerve),  199 

Spiritualism,  674 


Stomach  (Movements  of  the),  475 

Strychnine,   110 

Suction,  359 

Supports,  adhesive,  27 

Sympathetic  (Great  System),  286,  289, 
322  ;    cranial,  292 

Syncineses,  283 

Syncope,  anaesthetic,  107 

Syndrome  of  Brown-Sequard,  274 

Syntheses,  chemical,  252  ;    psychical,  652 

Syringomyelia,  509 

Systematic  (Functions),  116 

Systems,  peripheral,  deep,  121  ;  fvmctional 
of  nem-ons,  245  ;  simple  and  complex, 
284 ;  cerebro-spinal  and  great  sym- 
pathetic, 288  ;  of  the  life  of  relation, 
and  of  the  vegetative  life,  312  ;  sen- 
sorial, 469 

T 

Taste  buds,  645 

Taste  (Nerves  of),  646 

Territories,  radicular,  cutaneovis,  145 ; 
radicular,  muscular,  149  ;  excitable  of 
the  brain,  460 

Thalamus,  398 

Tone,  affective,  400 

Tonus,  muscular,  609 

Tracts,  cerebellar,  267  ;  of  Gowers,  268  ; 
lateral,  deep  and  fimdamental,  269 ; 
pyramidal  and  fundamental,  277  ;  mar- 
ginal anterior,  278  ;  of  the  optic  nerve, 
macular  and  perimacular,  direct  and 
crossed,  562 

Tract,  posterior,  longitudinal,  358  ;  ol- 
factory, 641  ;    optic,  556 

Trophic  (Disturbances),  152,  179  ;  nerves, 
248 

Trunk  (Movements  of  the),  525 

U 

Uniformity  of  functi(m  of  tiio  nervo  olo  ■ 

ments,    489 
Unilaterality  (of  movements),  534,  53") 
Unities,  electrical,  52 
Unity,  static,  dynamic,  5 

V 

Variation,  negative,  77  ;  positive,  82  ; 
oscillatory,  82 

Vaso-motors  of  the  spinal  cord,  135  ;  of 
the  brain,  456 

Vermis  (Destruction  of  the),  394  ;  (Ex- 
citation), 394 

Vertebral  (Nerve),  339 

Vertebral  (Theory),  155 

Vertigo,  612  ;    cerebellar,  393 

Vestibule,  606 

Vital  knot,  361 

Vomiting,  363 

W 

Waller  (Laws  of),  33 

Welding  of  the  nerves,  47 

Words  (Formation  of),  648 

Z 

Zones,  of  ansesthesia  of  the  skin,  145  ; 
motor  of  the  brain,  528  ;  sensori-motor, 
512;    of  language,  531,  669 


COLUMBIA  UNIVERSITY  LIBRARIES 

This  book  is  due  on  the  date  indicated  below,  or  at  the 
expiration  of  a  definite  period  after  the  date  of  borrowing, 
as  provided  by  the  rules  of  the  Library  or  by  special  ar- 
rangement with  the  Librarian  in  charge. 

DATE  BORROWED 

DATE  DUE 

DATE  BORROWED 

DATE  DUE 

i 

JQ     3  1942 

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